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Marine ecosystems are full of unique microbial phenomena, among them bioluminescence that could be harnessed for different ecological functions. This study was conducted to isolate luminous bacteria and utilize their glowing properties as a potential biosensor for toxicity assessment designs. It is worth noting that this study is the first report on the isolation of an Octopus associated Photobacterium species from Alexandria, Egypt. Based on light intensity, strain Photobacterium sp. EAH3 was selected and identified using 16S-rRNA gene sequencing. The luminescence production was further optimized using experimental. Among eight tested variables, the Plackett-Burman design showed that yeast extract, glycerol, peptone, and NaCl were the most important factors affecting luminescence. The central composite design calculated the optimum concentration of these variables in the optimized medium, which enhanced the bioluminescence activity by 1.39 folds. The employment of Photobacterium sp. EAH3 as a biosensor for the toxicity assessment of some solvents, hydrocarbons and heavy metals was examined using bioluminescence inhibition assay. According to the IC 50 results, the highest toxicity values recorded were 0.004 M, 4.15 ppm and 1.4 ppm for isoamyl alcohol, Hg2+ and catechol, respectively. Moreover, our study sheds light on futuristic methodology for monitoring toxicity in real polluted environmental and effluents' samples reflecting its promising efficiency. [ABSTRACT FROM AUTHOR]

ZIF-67, as a typical MOF material, is considered a new type of high-potential adsorbent due to its ample surface area and tunable surface chemistry, which has the potential to interact with other contaminants in unforeseen ways, resulting in combined toxicity. To further elucidate this possibility, we chose typical bisphenol compound (BP) which is widely used in commercial manufacturing, to explore the combined toxicity with MOF. MOF showed a high adsorption capacity for BPAF (> 80 %) and the weakest adsorption capacity for BPA (< 10 %), and DFT confirmed the different interaction strengths of MOF for BPs. The difference in adsorption capacity for BPs resulted in different amounts of free BPs, contributing to combined toxicity. Based on flow cytometry and TEM, the results showed that membrane damage was reduced and the ability of ZIF-67 to enter the cell was decreased in the low-concentration ZIF-67 mixing group, and the ability of ZIF-67 to enter the cell was increased in the high-concentration ZIF-67 mixing group, and the membranes were severely damaged. RT-PCR and biochemical indicators measurements helped to explain the underlying toxicity mechanism. This study is of practical significance for the development of environmental guidelines for mixed contaminant effects and accurate risk assessments. [Display omitted] • Combined effects of ZIF-67 and bisphenol compounds (BPA, BPS and BPAF) to Photobacterium phosphoreum. • MOF showed a high adsorption capacity for BPAF and the weakest adsorption capacity for BPA. • The difference in adsorption capacity for BPs resulted in different amounts of free BPs, contributing to the combined toxicity. • Oxidative damage and luminescence damage are the main reasons for combined toxicity. [ABSTRACT FROM AUTHOR]

• The bioavailability of iron may be correlated with the growth of A. pacificum (Group IV). • Siderophores produced by bacteria may facilitate the provision of bioavailable iron for A. pacificum. • Hydroxamate siderophores may serve as specific agents for the efficient uptake of iron. • Bacteria may influence STX toxicity and the synthesis of A. pacificum in conditions of iron scarcity. Specific bacterial species induce algal blooms by producing growth-promoting substances, such as siderophores, under iron-limited conditions. However, the molecular mechanisms underlying these effects remain poorly understood. This study investigates the interactions between the harmful dinoflagellate Alexandrium pacificum (Group IV) and siderophore-producing bacteria, with a focus on iron acquisition facilitated by bacterial siderophores. During algal bloom seasons in the South Sea of Korea, Photobacterium sp. TY1-4 was isolated, which enhances A. pacificum cell density under iron-deficient conditions, TY1-4 can use the sterile exudates from A. pacificum as the sole source of carbon , suggesting a mutualistic relationship. Transcriptomic and genomic analyses revealed siderophore-mediated redox-based signaling and non-reductive pathways enhancing iron bioavailability. Photobacterium sp. TY1-4 initiates siderophore production through quorum sensing, whereas A. pacificum utilizes specific receptors and transporters for hydroxamate-type siderophores (ApFHUA and ApFHUC) to uptake iron. Three redox key iron-uptake genes were also identified in A. pacificum : membrane-bound ferroxidase ApFET3 , high-affinity iron permease ApFTR1 , and ferric-chelate reductases/oxidoreductases ApFRE1 , with transcription levels inversely related to bioavailable iron. Increased iron bioavailability mediated by siderophores alleviates iron stress in A. pacificum , supporting its growth in iron-scarce environments. Additionally, A. pacificum co-cultured with Photobacterium sp. TY1-4 synthesized high-toxicity STXs, including GTX4, GTX2, and STX. These findings highlight the critical role of bacterial siderophores in iron binding and their potential impact on harmful algal bloom dynamics. [Display omitted] [ABSTRACT FROM AUTHOR]

Chondroitin sulfate (CS)/dermatan sulfate (DS) lyases play important roles in structural and functional studies of CS/DS. In this study, a novel CS/DS lyase (enCSase) was identified from the genome of the marine bacterium Photobacterium sp. QA16. This enzyme is easily heterologously expressed and purified as highly active form against various CS, DS and hyaluronic acid (HA). Under the optimal conditions, the specific activities of this enzyme towards CSA, CSC, CSD, CSE, DS and HA were 373, 474, 171, 172, 141 and 97 U/mg of proteins, respectively. As an endolytic enzyme, enCSase degrades HA to unsaturated hexa- and tetrasaccharides but CS/DS to unsaturated tetra- and disaccharides as the final products. Sequencing analysis showed that the structures of tetrasaccharides in the final products of CS variants were not unique but were highly variable, indicating the randomness of substrate degradation by this enzyme. Further studies showed that the smallest substrate of enCSase was octasaccharide for HA but hexasaccharide for CS/DS, which could explain why this enzyme cannot degrade HA hexa- and tetrasaccharides and CS/DS tetrasaccharides further. It is believed that enCSase may be a very useful tool for structural and functional studies and related applications of CS/DS and HA. • A novel chondroitin sulfate (CS)/dermantan sulfate (DS) lyase (enCSase) was identified. • The enCSase has quite high endolytic activities against CS, DS and hyaluronic acid. • The substrate-degrading pattern and product structures of enCSase were studied in detail. • This study provides a very useful enzyme with clear enzymatic properties for the studies of CS/DS. [ABSTRACT FROM AUTHOR]

The effects of high hydrostatic pressure (HHP) treatments on histamine-forming bacteria (HFB) Morganella morganii and Photobacterium phosphoreum in phosphate buffer and tuna meat slurry were investigated using viability counting and scanning electron microscopy. The first-order model fits the destruction kinetics of high pressure on M. morganii and P. phosphoreum during the pressure hold period. The D-values of M. morganii (200 to 600 MPa) and P. phosphoreum (100 to 400 MPa) in phosphate buffer ranged from 16.4 to 0.08 min and 26.4 to 0.19 min, respectively, whereas those in tuna meat slurry ranged from 51.0 to 0.09 min and 71.6 to 0.19 min, respectively. M. morganii had higher D-values than P. phosphoreum at the same pressure, indicating it was more resistant to HHP treatment. HFB had a higher D-value in tuna meat slurry compared with that in phosphate buffer, indicating that the HFB were more resistant to pressure in tuna meat slurry. The Zp values (pressure range that results in a 10-fold change in D-value) of M. morganii and P. phosphoreum were 162 and 140 MPa in phosphate buffer and 153 and 105 MPa in tuna meat slurry, respectively. Damage to the cell wall and cell membrane by HHP treatments can be observed by scanning electron microscopy. To our knowledge, this is the first report to demonstrate that HHP can be applied to inactivate the HFB M. morganii and P. phosphoreum by inducing morphological changes in the cells. M. morganii with higher D-values was more resistant than P. phosphoreum at the same HHP. HFB with higher D-values were more resistant in fish slurry than in phosphate buffer. P. phosphoreum with lower Zp values was more sensitive to changes in HHP than M. morganii. SEM shows that HHP causes cell wall and membrane damage in HFB. [ABSTRACT FROM AUTHOR]

The New Zealand Greenshell™ mussel (Perna canaliculus) is an economically important aquaculture species. Prolonged increases in seawater temperature above mussel thermotolerance ranges pose a significant threat to mussel survival and health, potentially increasing susceptibility to bacterial infections. Using challenge experiments, this study examined the combined effects of increased seawater temperature and bacterial (Photobacterium swingsii) infection on animal survival, haemocyte and biochemical responses of adult mussels. Mussels maintained at three temperatures (16, 20 and 24 °C) for seven days were either not injected (control), injected with sterile marine broth (injection control) or P. swingsii (challenged with medium and high doses) and monitored daily for five days. Haemolymph and tissue samples were collected at 24, 48, 72, 96, 120 h post-challenge and analysed to quantify bacterial colonies, haemocyte responses and biochemical responses. Mussels infected with P. swingsii exhibited mortalities at 20 and 24 °C, likely due to a compromised immune system, but no mortalities were observed when temperature was the only stressor. Bacterial colony counts in haemolymph decreased over time, suggesting bacterial clearance followed by the activation of immune signalling pathways. Total haemocyte counts and viability data supports haemocyte defence functions being stimulated in the presence of high pathogen loads at 24 °C. In the gill tissue, oxidative stress responses, measured as total antioxidant capacity and malondialdehyde (MDA) levels, were higher in infected mussels (compared to the controls) after 24h and 120h post-challenge at the lowest (16 °C) and highest temperatures (24 °C), indicating the presence of oxidative stress due to temperature and pathogen stressors. Overall, this work confirms that Photobacterium swingsii is pathogenic to P. canaliculus and indicates that mussels may be more vulnerable to bacterial pathogens under conditions of elevated temperature, such as those predicted under future climate change scenarios. [Display omitted] • Higher mussel mortality with combined temperature and bacterial stressors. • Reduction of bacterial colonies in haemolymph with high temperature exposure. • Haemocyte parameters fluctuated with changes in temperature and over time. • Bacterial infection elicits oxidative stress at 16 and 24 °C. [ABSTRACT FROM AUTHOR]

Photobacterium damselae subsp. damselae (PDD) is a pathogenic bacterium with wide distribution, a broad spectrum of host infection, and a high mortality rate in infected animals. Therefore, it is considered one of the most dangerous pathogenic bacterial species in mariculture worldwide. Among the current alternative aquatic disease preventive therapies, phage therapy has attracted widespread attention due to its strong specificity, fast effects, non-toxicity, and lack of pollution. In this study, we identified a bacteriophage that can specifically lyse PDD in the silver pomfret culture environment. The genetic material of the bacteriophages was confirmed to be DNA. Additionally, we studied the effects of bacteriophages under different environmental conditions. Furthermore, we also conducted treatment experiments on silver pomfret using this bacteriophage, and the results showed that the phage had a certain protective effect on silver pomfret infected with PDD. In summary, we isolated and screened a bacteriophage with relatively stable biological properties against PDD , providing a certain theoretical basis for preventive strategies against PDD infection in silver pomfret mariculture. • A bacteriophage that can specifically lyse PDD in the silver pomfret culture environment has been identified. • The genetic material of the bacteriophages was confirmed to be DNA. • The effects of bacteriophages under different environmental conditions were studied. • The isolated Phage-I had a certain protective effect on silver pomfret infected with PDD. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework (ZIF) is of wide interest in biomedical applications due to its extraordinary properties such as high storage capacity, functionality and favorable biocompatibility. However, more comprehensive safety assessments are still essential before ZIF is broadly used in biomedicine. Using the characteristic that aldehyde groups on the surface of ZIF-90 can be modified with other functional groups, a series of ZIF-90s modified with different functional groups (oxime group, carboxyl group, amino group and sulfhydryl group) were synthesized to investigate the effect of functionalization on the toxicity of ZIF-90. ZIF-90 series showed concentration-dependent toxic effects on Photobacterium phosphoreum T3 and the functionalized ZIF-90s are more toxic than pristine ZIF-90, with the ZIF-90 modified with amino group (ZIF-90-NH 2) showing the strongest toxicity (IC 50 = 23.06 mg/L). Based on the results of the cellular assay and stability exploration, we concluded that corresponding imidazole-ligand release and the property of positively charged are responsible for the elevated toxicity of ZIF-90-NH 2. Cell membrane damage, oxidative damage and luminescence damage are the main contributors to the toxic effects of ZIF-90 series. This study explored the effect of surface functionalization on the toxicity of ZIF and proposed mechanistic clues for the safety application of ZIF. [Display omitted] • The ZIF-90 modified with different groups exhibited more toxicity than ZIF-90. • The ZIF-90 modified with amino group showed the strongest toxicity. • Ligand release increases the toxicity of positively charged ZIF-90-NH 2. • Zn released from the ZIF-90 series was not the main contributor to the toxicity. • ZIF-90 series showed oxidative damage and luminescence damage to T3 strain. [ABSTRACT FROM AUTHOR]

Market globalization and changes in purchasing habits pose a challenge to the fishery industry because of the short shelf life of fish products. In view of this scenario, it would be very helpful if tools capable of predicting the shelf-life of fish could be developed. Thus, the objective of this study was to employ a modelling approach capable of predicting the evolution of the microbiota of hake fillets packaged under a modified atmosphere (MAP) rich in CO 2 (50% CO 2 / 50% N 2) when stored at temperatures ranging between 1 and 10 °C. Growth curves of ten microbial groups were obtained at four different temperatures and fitted with the Baranyi model. Photobacterium showed high growth rates in hake fillets (0.99 days−1 at 4 °C), similar to those of Shewanella , lactic acid bacteria, and non-specific microbial groups investigated, and significantly higher than those of Pseudomonas. Furthermore, no lag phase was observed for Photobacterium regardless of the temperature investigated. On the other hand, Enterobacteriaceae and moulds and yeasts displayed low growth fitness, and their counts increased by <1.5–2 Log 10 cycles along the incubation period regardless of storage temperature. The influence of storage temperature on growth parameters (λ, μ max and Y end) was subsequently studied, and secondary models were developed for the eight most relevant microbial groups. All of the final equations developed in this study showed R2 values ≥0.90, and RMSE values ≤0.50. In addition, results obtained in this investigation strongly suggest that Photobacterium would be the main responsible microorganism for the spoilage of hake fillets stored under MAP conditions (50% CO 2 /50% N 2) along the entire range of temperatures investigated (1–10 °C). Unlabelled Image • The influence of temperature on microbial growth in MAP hake fillets was studied. • Primary and secondary models for different microbial groups have been developed. • Photobacterium , Shewanella and lactic acid bacteria showed the higher growth rates. • Photobacterium displayed the shortest lag phase among the microbial groups studied. • Photobacterium would be the main cause of the spoilage of MAP hake fillets. [ABSTRACT FROM AUTHOR]

The tert -butylphenols (TBPs) are one group of alkylated phenolic compounds with wide applications in UV absorbers and antioxidants. They are becoming contaminants of emerging concern with residues frequently detected in natural surface water or drinking water. The direct sunlight may photolyze TBPs in waters and affect their aquatic toxicities; however, such data are very limited. In the present study, we investigate the photodegradation of 2,6-DTBP by direct sunlight in water and compare the aquatic toxicities of 2,6-DTBP with that of its product toward Photobacterium phosphoreum. 2,6-DTBP is photodegraded by 71.31 ± 2.64% under simulated sunlight following a pseudo-first-order kinetics with rate constant (k) of 0.061 h−1. Density functional theory simulations at M06–2X/def2-SVP level reveal that the photodegradation occurred sequentially through oxidation, photo-isomerization and hydrogenation. The degradation product 2,5-DTBP is toxic to P. phosphoreum (EC 50 3.389 × 10−5 mol/L) whereas 2,6-DTBP is not harmful (EC 50 3.917 × 10−3 mol/L) as designated by the European Union Standard, indicating the enhanced toxicities driven by the direct sunlight photodegradation. We demonstrate the enhanced toxicities of 2,6-DTBP by natural sunlight, suggesting that negligence of photodegradation of TBPs-related contaminants will underestimate the comprehensive risk of these emerging contaminant in natural waters. Image 1 • 2,6-DTBP is photodegraded by > 70% after 24 h natural sunlight irradiation. • The photodegradation of 2,6-DTBP follows the pseudo-first-order kinetics. • 2,6-DTBP is photodegraded via oxidation, photo-isomerization and hydrogenation. • 2,5-DTBP is the major degradation product of 2,6-DTBP. • 2,5-DTBP exhibits higher toxicity toward Photobacterium phosphoreum than 2,6-DTBP. 2,6-DTBP was photodegraded by > 70% after 24 h natural sunlight irradiation and its product 2,5-DTBP exhibits higher toxicity toward Photobacterium phosphoreum. [ABSTRACT FROM AUTHOR]

An efficient heterotrophic nitrifying/aerobic denitrifying strain, Photobacterium sp. NNA4 was isolated from a recirculating aquaculture system (RAS). NNA4 was capable of utilizing ammonia, nitrate or nitrite as sole N-source with maximal removal rates of 12.5 mg/L/h for NH 4 + N, 16.4 mg/L/h for NO 3 --N, and 4.5 mg/L/h for NO 2 --N, respectively. Optimal nitrification conditions were: sodium succinate as C-source, 30–37°C, NaCl 1–4%, pH 7.0–8.0, dissolved oxygen 5.89 mg/L, C/N > 10. Gas chromatography/mass spectrometry and gas chromatography/isotope ratio mass spectrometry analyses showed that N 2 and N 2 O were aerobic denitrification products of nitrite and nitrate. NNA4 could tolerate high concentration of hydroxylamine and displayed efficient hydroxylamine-transforming capability. Hydroxylamine oxidoreductase activity using potassium ferricyanide as electron acceptor was 0.042 U. Results revealed that strain NNA4 could oxidize NH 2 OH directly to N 2 O at aerobic conditions. In view of its high removal ability of inorganic nitrogen pollutants and broad salinity tolerance range, NNA4 has great potential in denitrification treatment of types of wastewater with either low salinity (e.g., municipal facilities) or high salinity (e.g., aquaculture, seafood processing). • Photobacterium sp. NNA4 is an efficient heterotrophic nitrifier/aerobic denitrifier. • Heterotrophic nitrification/aerobic denitrification of its genus had not reported. • It efficiently transforms hydroxylamine to nitrite and N 2 O. • Our findings support the hypothesis of hydroxylamine metabolism pathway. [ABSTRACT FROM AUTHOR]

Abstract Photobacterium damselae subsp. piscicida (P. damselae subsp. piscicida) is the agent of Photobacteriosis, a serious fish disease that produces an acute infection and high mortality in farmed cobia. It has been proved that regulation of pro- and anti-inflammatory cytokines play a central role in initiation of proper inflammatory responses against bacterial infection. Here we have analyzed the expression of pro-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-8 and IFN-ɤ) and anti-inflammatory cytokines (IL-10 and IL-11) in spleen and head kidney during acute P. damselae subsp. piscicida infection of cobia. Our data revealed that cytokines tested showed distinct patterns of expression. While TNF-α and IL-8 showed a decay pattern of expression, IL-1β response was quite late. Moreover, P. damselae subsp. piscicida infection induced the simultaneous expressions of pro-inflammatory (IL-6, IFN-ɤ) and anti-inflammatory (IL-10, IL-11) cytokines. Together these results indicate the innate immunity of cobia is actively suppressed by P. damselae subsp. piscicida. Highlights • IL-6, IL-10, IL-11 and IFN-ɤ have been identified in cobia. • The expression pattern of cytokines was characterized by a depression of TNF-α and IL-8, a delayed response of IL-1β and simultaneous up-regulations of IL-6, IL-10, IL-11 and IFN-ɤ. • The cytokine disparity may explain the suppression of innate immunity by P. damselae subsp. piscicida in cobia. [ABSTRACT FROM AUTHOR]

Abstract In July 2016 and August 2017, there were two severe outbreaks of serious skin ulcers in rockfish (Sebastes schlegeli), which were cultured in offshore net-cages around Daqing Island, China. One pathogenic bacterium was isolated from the skin lesions of diseased fish. Such isolate was identified as Photobacterium damselae subsp. damselae through morphological observation, physiological and biochemical tests as well as gyr B gene sequencing. Artificial challenge test confirmed that this strain had strong pathogenicity to black rockfish and could cause serious skin ulcers. The symptoms were consistent with those of naturally infected fish. Its 14-day LD 50 in for black rockfish was 8.78 × 102 cfu/g body weight. Highlights • One full year epidemiological investigation for black rockfish was performed and twice skin ulcer disease were detected in the biggest offshore net-cage mariculture area in north China. • Photobacterium damselae subsp. damselae was isolated form diseased fish and confirmed to has high pathogenicity to black rockfish. [ABSTRACT FROM AUTHOR]

Abstract Microbial (colony counts, 16S rRNA gene amplification), chemical (pH, 1H NMR spectroscopy) and sensory changes in raw Atlantic Salmon (Salmo salar) and tuna (Thunnus albacares) fillets stored under vacuum at 3 °C were evaluated over a period of 12 days. Both species of fish are globally important and among the ten most consumed fishes in the world. Although the sensory analyses showed a decrease in the quality of both fish species, only the salmon fillets were considered spoiled at the end of the storage period. In salmon, trimethylamine was the main spoilage product and bacterial colony counts reached an average of 7.3 log10 cfu/g. The concentration of glucose decreased and the concentration of organic acids increased during storage revealing glucose fermentation. Photobacterium was the dominating genus in the salmon studied. In the tuna studied, the bacterial colony counts reached only an average of 4.6 log10 cfu/g. The dominating bacteria in tuna were Pseudomonas spp. Glucose levels did not decrease, suggesting that amino acids and lactate most likely acted as carbon sources for bacteria in tuna. In conclusion, the study revealed that salmon was clearly a more perishable fish than tuna. Highlights • Pseudomonas spp. was the dominating genus in tuna under vacuum. • Photobacterium spp. was the dominating genus in salmon under vacuum. • Lactate and amino acids were important carbon sources for bacteria in tuna. • Glucose and TMAO were the precursors of spoilage metabolites in salmon. • TMA correlated with sensory evaluation quality in salmon. [ABSTRACT FROM AUTHOR]

This study aimed to explore the diversity of fifty-four Photobacterium strains isolated from muscle tissue of European plaice (Pleuronectes platessa) caught at different fishing seasons and stored 14-days under various conditions. Single phylogenetic markers (16S rRNA, gapA , gyrB and recA) and multilocus sequence analysis (MLSA) were employed to classify isolates at species level. Furthermore, intra- and interspecies variability in the phenotypic traits, maximum specific growth rate (μ max) and spoilage potential of the Photobacterium isolates were investigated. The isolates were classified into the P. iliopiscarium (53.7 %), P. phosphoreum (40.7 %) and P. piscicola (5.6 %) clades using MLSA. Two housekeeping genes, gyrB and recA , exhibited a consistent phylogenetic relationship with MLSA, suggesting that they might be used as individual phylogenetic markers for the Photobacterium genus. Intra- and interspecies variability in the expression of phenotypic characteristics and the production of trimethylamine (TMA), inosine (HxR), and hypoxanthine (Hx) were observed. A growth optimum temperature for P. iliopiscarium was approximately 20 °C, while those for P. phosphoreum and P. piscicola were closer to 15 °C. All isolates exhibited the highest growth density at 1.5 % NaCl, followed by 0.5 %, 3 %, and 6 % NaCl. However, P. phosphoreum demonstrated a higher NaCl tolerance than the other two species. Although, the high CO 2 atmosphere significantly inhibited the growth of all strains at 4 °C, P. phosphoreum and P. piscicola showed higher growth density at 15 °C than P. iliopiscarium. Notably, all strains demonstrated H 2 S production. The μ max varied considerably within each species, highlighting the significance of strain-level variability. This study demonstrates that P. iliopiscarium and P. piscicola , alongside P. phosphoreum , are efficient TMA-, HxR-, Hx-, and H 2 S-producers, suggesting their potential contribution to synergistic off-odour generation and spoilage. Moreover, the Photobacterium isolates seem to exhibit diverse adaptations to their environments, resulting in fluctuated growth and spoilage potential. Understanding intra- and interspecies variability will facilitate modelling seafood spoilage in microbial risk assessments and developing targeted hurdles to prolong products' shelf-life. • P. iliopiscarium , P. phosphoreum and P. piscicola were identified. • Inter- and intraspecies variability were found in the phenotypic traits. • All strains demonstrated hydrogen-sulfide production. • Isolates' growth rates varied in strain and species level. • Trimethylamine, inosine and hypoxanthine yield factors exhibited variations in strain level. [ABSTRACT FROM AUTHOR]

Photobacterium damselae subsp. damselae (PDD) is a dangerous bacterial disease that affects silver pomfret (Pampus argenteus) and its main virulence factors are pore-forming toxins. In this study, a highly pathogenic strain was obtained from naturally infected silver pomfret and was introduced into healthy fish for experimentation. Liver, gill, kidney and spleen samples were collected at 0, 24, 48, 72 and 96 h. Histopathological evaluations of these tissues, via HE staining, showed multi-organ bleeding, inflammatory infiltration and histopathocyte vacuolation as the main pathological changes. The levels of AKP, ACP, LZM, SOD, GSH and CAT in serum also displayed an increase following infection. Transcriptome sequencing of liver, kidney and spleen was performed using samples 96 h post-infection. The analysis of the resulting 770,878,120 clean reads collectively assembled into 89,310 unigenes. The WGCNA analysis demonstrated enrichment of phagosome and cytokine-cytokine receptor interaction in the liver, drug metabolism-cytochrome P450 in the kidney, and MAPK signaling pathway and other signaling pathways in the spleen. DEGs related to immune and immune-related pathways, such as Phagosome, Autophagy-animal and Glycerolipid metabolism, were significantly enriched. Selected key genes from these KEGG pathways were examined using RT-qPCR. The expression level of autophagy related genes (pi3k, bcl2) increased after infection, while the gene associated with MAPK and apoptosis (Caspase 9, mapk4) significantly increased after 72 h infection. The expression of phagosome related genes (atp6v1f, ctsl) increased initially, but later decreased. The genes related to innate immunity (ccl4, il15) were up-regulated, while those related to acquired immunity (mhc2a, mhc2b) showed a downward trend. Lysosome-related genes (gilta, giltb, cftr, c-type lectin, m6pra and m6prb) were up-regulated in liver and spleen and down-regulated in kidney and gill. The data obtained illustrated that PDD activated the immune defenses of the fish, increasing metabolic expenditure, but that the pore-forming toxins released by PDD could destroy the phagosome membrane and help the bacteria escape, which could disturb antigen presentation and inhibit the activation of the acquired immunity. This study reveals the potential immune escape mechanism of PDD in the host for the first time and has the potential to aid in the development of anti-PDD drugs. • PDD infection caused multi-organ bleeding, inflammatory infiltration in fish tissues. • Immune relating enzyme activities increased after PDD infection. • PDD activated the immune defenses and increased metabolic expenditure. • Pore-forming toxins of PDD might destroy phagosome and help PDD escape. • This immune escape might disturb antigen presentation and inhibit acquired immunity. [ABSTRACT FROM AUTHOR]

The unique properties of polyaniline (PANI), as representative of conducting polymers (CPs) predetermine their use in biomedical field. While the material properties of PANI prepared by chemical or microwave synthesis are well known, their biological properties have not been adequately addressed and compared. To fill this gap, PANI powders were prepared by either chemical or microwave synthesis using different oxidizing agent (ammonium persulfate, APS vs potassium iodate, KIO 3) and studied. The effect on cytotoxicity and ecotoxicity were determined according to the ISO protocol and inhibition of bioluminescence in Photobacterium phosphoreum , respectively. The significant effect of both factors, the synthesis route and oxidizing agent, on biological performance was confirmed. The choice of optimum preparation condition for PANI synthesis highly improved its cytotoxicity and ecotoxicity compared to previously described PANI forms. Results of the here presented work are crucial for the further utilization of PANI in wide spectrum of biomedical applications. [Display omitted] • KIO 3 oxidizing agent reduced PANI cytotoxicity in contrast to APS. • Method of preparation did not influence PANI's cytotoxicity before purification step. • MW-PANIKIO3_P sample showed lower cytotoxicity than CS-PANIKIO3_P after purification. • The cytotoxicity for PANIAPS were not affected by preparation method or purification. • PANI low ecotoxicity can be achieved by using KIO 3 , MW method and purification step. [ABSTRACT FROM AUTHOR]

Highlights • Extrusion technology results in a better carbohydrate utilization such as protein sparing effect. • Carbohydrate-free diets induced a higher microbial variability along the intestinal tract in Totoaba macdonaldi. • The high digestible carbohydrates in the ED diet favours a relative abundance of Vibrio spp. and Photobacterium Abstract The effect of extrusion process in aquafeeds for juvenile totoaba (Totoaba macdonaldi) on the microbiome diversity from four different intestinal sections and overall growth performance was evaluated. The extrusion process clearly improved the protein efficiency ratio (PER) and the apparent digestibility coefficient (ADC) compared to the modified extruded diet (MED) without pressure and high temperature; demonstrating the advantage of the use of extrusion technology. After 17 days of feeding, the microbiome analysis revealed that the taxa relative abundance at the phylum level in the four gut sections was modified according to the dietary treatment. Vibrio , Photobacterium , and Shimia , colonize the intestine of totoaba fed with extruded diet, while the genus Ruegeria was observed almost at constant levels in both dietary treatments, in most of the intestinal sections. The latter is known to promote the fish health. This work demonstrates that extrusion processes affect the intestinal microbiome and enhances the performance of fish diets. [ABSTRACT FROM AUTHOR]

Abstract Three strains, H01100409BT, H01100413B, and H27100402HT, were isolated from several internal organs of diseased redbanded seabream (Pagrus auriga) reared in Andalusia (Southern Spain). All strains were studied by phenotypic, including chemotaxonomy, and genomic characteristics. Phylogenetic analysis based on concatenated sequences of six housekeeping genes (gyrB , ftsZ , topA , mreB , gapA , and 16S rRNA) supported the inclusion of the strains within the clade Phosphoreum of the genus Photobacterium , and two of the strains (H27100402HT and H01100409BT) formed a tight group separated from the closest species P. aquimaris. Genomic analyses, including average nucleotide identity (ANIb and ANIm) and DNA–DNA hybridization (DDH), clearly separated strains H27100402HT and H01100409BT from the other species within the clade Phosphoreum with values below the thresholds for species delineation. The chemotaxonomic features (including FAME analysis and MALDI-TOF-MS) of H27100402HT and H01100409BT strains confirmed their differentiation from the related taxa. The results demonstrated that strain H01100413B was classified as P. aquimaris and the strains H27100402HT and H01100409BT represented a new species each in the genus Photobacterium , for which we propose the names Photobacterium malacitanum sp. nov., type strain H27100402HT (=CECT 9190T = LMG 29992T), and Photobacterium andalusiense sp. nov., type strain H01100409BT (=CECT 9192T = LMG 29994T). [ABSTRACT FROM AUTHOR]

Photobacterium species are members of the bacterial communities typically associated with scombrotoxin-forming fish. Reclassification and discovery of new Photobacterium species has caused confusion as to which species are capable of biogenic amine production. We analyzed histamine, cadaverine, and putrescine production by 104 Photobacterium strains representing 23 species. The presence of the genes for histidine decarboxylase (hdc), lysine decarboxylase (ldc), and ornithine decarboxylase (odc) was determined by real-time or conventional PCR and whole genome sequencing. Significant histamine production (.> 200 ppm) was detected in five Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. damselae, and P. phosphoreum. The hdc gene was detected in all of these histamine-producing species except P. phosphoreum. Cadaverine was produced by eight Photobacterium species: P. angustum, P. aquimaris, P. damselae, P. iliopiscarium, P. kishitanii, P. leiognathi, P. mandapamensis, and P. phosphoreum. Putrescine was produced by six Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. leiognathi, P. mandapamensis, and Photobacterium sp. Cadaverine production correlated closely with the presence of the ldc gene, but putrescine production did not correlate closely with the presence of the odc gene. Characterization of the biogenic amine production by Photobacterium species will allow identification of these marine bacteria and help ensure that current guidelines account for mitigation of these bacteria. [ABSTRACT FROM AUTHOR]

In the summer of 2015, a disease outbreak occurred in the Silver pomfret ( Pampus argenteus ) that reared in indoor tanks of one farm in Eastern China. The primary external sign of affected fish was hemorrhages in fins. In the present study, Gram-negative rods were found in internal organs of diseased fish, and bacterial isolates obtained were identified as Photobacterium damselae subsp. damselae based on phenotypic and genetic analysis. Pathogenicity of one representative P. damselae subsp. damselae isolate was confirmed with experimental infections using healthy silver pomfret. This bacterial isolate also exhibited high cytotoxicity to against a marine finfish kidney cell line. In summary, P. damselae subsp. damselae was the causative agent of the disease outbreak of 2015 in aquacultured sliver pomfret. [ABSTRACT FROM AUTHOR]

The immune responses and protection efficacy of a vaccine containing inactivated formalin-killed Photobacterium damselae subsp. piscicida formulated with alum and different unmethylated Cytosine phosphorothioate Guanine oligodeoxynucleotides (CpG-ODN, including 2006, 2395, 1668, and control ODN 2137) as the adjuvant were investigated in cobia Rachycentron canadum . Results showed that, formulation with CpG-ODN 1668 significantly ( P  < .05) increased the expression of rctlr9a (11 and 20 fold in spleen and liver, respectively) and il-1β (4 fold in liver) in immunized fish. The highest lysozyme and peroxidase activities were also observed in fish immunized with CpG-ODN 1668 formulation. In addition, compared to other treatments, bactericidal activity using the bacterial survival percentage was significantly less in CpG-ODN 1668 formulation (25%). The antibody titer was significantly higher at 6 and 21 dpi from CpG-ODN 1668 (OD = 0.27 ± 0.02) and CpG-ODN 2006 (OD = 0.24 ± 0.018) formulations. Fish immunized with CpG-ODN 1668 and 2395 formulations protected R. canadum with survival rate of 90 & 70% by P. damselae subsp. piscicida until 3 weeks post-challenge. This study has indicated that different tlr9 agonists have different abilities to augment immune response and protection against Photobacterium. CpG-ODN 1668 can be used as an adjuvant for R. canadum vaccination. [ABSTRACT FROM AUTHOR]

Uncontrolled bacterial growth and metabolic activities are responsible for the short shelf life of raw pork. Culture-independent analysis by 16S ribosome cDNA could reveal viable bacteria in raw pork. This study investigated microbial growth and volatile organic compounds of raw pork supplemented with various preservatives. Vacuum-packaged raw pork was stored at 4°C, after soaking in solutions of potassium sorbate, ε-poly-L-lysine, kojic acid (KA), or sodium diacetate, individually. Spoilage of raw pork was monitored by determining pH and total volatile basic nitrogen, whereas bacterial growth was determined by culture-dependent and culture-independent analyses. Data indicated that all the preservatives were able to inhibit bacterial growth and extend the shelf life of pork. High-throughput sequencing of 16S ribosome cDNA indicated that Pseudomonas was inhibited under vacuum conditions, whereas facultative anaerobes (Acinetobacter, Photobacterium, Brochothrix, and Myroides) were the most active genera in the spoiled pork. Photobacterium was further inhibited by each preservative. The inhibition of Acinetobacter, Photobacterium, and Myroides could be responsible for the extended shelf life of vacuum-packaged pork; they were effectively inhibited by KA, which also induced the longest shelf life. Moreover, 19 types of volatile organic compounds were detected. 3-Methylbutanol, 3-methylbutanol acetate, 2-butanone, toluene, benzeneacetaldehyde, dimethyl trisulfide, and acetoin were associated with spoilage. Furthermore, KA is a potential preservative in raw pork; because no phenol was detectable within 35 days, excessive intake of phenol induced by preservatives was avoided. [ABSTRACT FROM AUTHOR]

The advent of high-throughput sequencing technologies in recent years has revealed the unexpected presence of genus Photobacterium within the chicken meat spoilage ecosystem. This study was undertaken to decipher the occurrence, the growth patterns and the genotypic biodiversity of Photobacterium phosphoreum on chicken breast fillets stored aerobically at 4 °C through conventional microbiological methods and molecular techniques. Samples were periodically cultured on marine broth agar (MA; supplemented with meat extract and vancomycin) for the enumeration of presumptive bioluminescent Photobacterium spp. In total, 90 bioluminescent bacteria were recovered from the initial (time of first appearance), middle and end stages of storage. Concomitantly, 95 total psychrotrophic/psychrophilic bacteria were isolated from the same medium to assess the presence and diversity of non-luminous photobacteria. Genetic diversity between bioluminescent isolates was assessed with two PCR-based DNA fingerprinting methods, i.e. RAPD and rep-PCR. Moreover, the characterization of selected bacterial isolates at the genus and/or species level was performed by sequencing of the 16S rRNA and/or gyr B gene. Bioluminescent bacteria were scarcely encountered in fresh samples at population levels of ca. 2.0 log CFU/g, whilst total psychrotrophic/psychrophilic bacteria were found at levels of ca. 4.4 log CFU/g. As time proceeded and close to shelf-life end, bioluminescent bacteria were encountered at higher populations, and were found at levels of 5.3 and 7.0 log CFU/g in samples from the second and third batch, respectively. In the first batch their presence was occasional and at levels up to 3.9 log CFU/g. Accordingly, total psychrotrophic/psychrophilic bacteria exceeded 8.4 log CFU/g at the end of storage, suggesting the possible underestimation of bioluminescent populations following the specific cultivation conditions. Sequence analysis assigned bioluminescent isolates to Photobacterium phosphoreum , while genetic fingerprinting revealed high intra-species variability. Respectively, total psychrotrophs/psychrophiles were assigned to genera Pseudomonas , Shewanella , Psychrobacter , Acinetobacter , Vibrio and Photobacterium. Non-luminous photobacteria were not identified within the psychrotrophs/psychrophiles. Results of the present study reveal the intra- and inter-batch variability on the occurrence and growth responses of P. phosphoreum and highlight its potential role in the chicken meat spoilage consortium. • Insights into genetic variability of bioluminescent photobacteria in refrigerated chicken breast fillets. • P. phosphoreum levels varied within and between batches in fresh and spoiled samples. • P. phosphoreum population was found at levels potentially connected with spoilage processes. • Non-luminous photobacteria were not detected in spoilage microbiota. [ABSTRACT FROM AUTHOR]

In this study, a high-efficiency colorimetric sensor for water toxicity assessment was successfully constructed by the visual analysis with naked eyes and the high-throughput measurement with a microplate reader. The bioluminescent Photobacterium phoshoreum T3 spp. (T3) and Prussian blue (PB) were used as model bacterium and indicator of the colorimetric sensor, respectively. In order to accurately detect acute toxicities of wastewater, the experimental conditions, concentrations of cells, K 3 [Fe(CN) 6 ] and NaCl, reaction temperature and time, were optimized to be OD 600 = 2, 8 mM, 1.2%, 26.5 °C and 25 min, respectively. Then several samples of simulated wastewater containing Hg2+, Cd2+, Zn2+, 3,5-dichlorophenol (DCP) and formaldehyde (HCHO) were tested. The composite biotoxicity of dry battery leachate and real water sample was also evaluated. The IC 50 values of Hg2+, Cd2+, Zn2+ and DCP obtained were 3.60, 1.56, 0.96 and 11.77 mg L−1, respectively. Moreover, a toxic unit (TU) model was applied to evaluate the binary complex toxicity of Hg2+ + Cd2+, Hg2+ + Zn2+ and DCP + Zn2+, which showed antagonistic effects. The work demonstrates that the promising high-efficiency sensor can detect quickly and sensitively the single and joint toxicities of multi-pollutants in water, which possesses extensive potentials in field of toxicity detection. • A promising colorimetric sensor has been developed using T3 as model bacterium. • High-efficiency detection of toxicity in water was realized through microplate reader. • Toxicities of individual, combined toxicants and real water were detected sensitively. • The critical concentrations can be detected sensitively in a 96-well plate with naked eyes. • The technology revealed a wide application prospect in the field of toxicity detection. [ABSTRACT FROM AUTHOR]

Trachinotus ovatus is an important economic species in China, with an annual output of over 100,000 tons (FAO). The major histocompatibility complex (MHC) genes, which are a highly polymorphic gene superfamily, play a vital role in the adaptive immune system. In our study, due to the threat caused by Photobacterium damselae , the associations between polymorphisms of exon 2 of MHC IIß and disease resistance/susceptibility were analysed in Trachinotus ovatus . The gene structure of MHC IIß was composed of six exons and five introns in T . ovatus , similar to Hippocampus erectus MHC IIß . Among the forty-three alleles, high levels of polymorphism were found (24.8% of nucleotide positions were variable). In the peptide-binding region (PBR) and non-PBR sites, the value of d N was 6.60 and 12.22 (> 1) times higher than the value of d S , respectively. Six alleles were chosen to calculate their distributions in the high-resistance (HR) and high-susceptibility (HS) groups. The analysis of the associations between alleles and resistance/susceptibility to P . damselae indicated that the TO-DAB-01 allele was associated with immunity to P . damselae and the TO-DAB-04, TO-DAB-05 and TO-DAB-10 alleles were associated with its sensitivity to P . damselae . The results suggest that the diversity of exon 2 of MHC IIß alleles could be used to explore the association between disease susceptibility/resistance and the multiformity of MHC IIß and to achieve the molecular-assisted selection of T . ovatus with enhanced disease resistance. [ABSTRACT FROM AUTHOR]

Analysis of spoilage-associated microbiota of modified-atmosphere packaged poultry meat revealed four different bacterial isolates that could not be assigned to known species. They showed a Gram-negative staining behavior, were facultatively aerobic, non-motile with variable cell morphology. Phylogenetic analysis of 16S rDNA and gyr B, rpo D and rec A revealed a distinct lineage within the genus Photobacterium with Photobacterium ( P .) iliopiscarium DSM 9896 T , P. phosphoreum DSM 15556 T , P. kishitanii DSM 19954 T , P. piscicola LMG 27681 T and P. aquimaris DSM 23343 T as closest relatives. The designated type strain TMW 2.2021 T is non-luminous and grew at 0–20 °C (optimum 10–15 °C), within pH 5.0–8.5 (optimum 6–8) and in the presence of 0.5–3% (w/v) NaCl (optimum 1%). Major cellular fatty acids of TMW 2.2021 T were summed feature 3 (C 16:1 ω 7 c /iso-C 15 3-OH), C 16:0 , C 18:1 ω 7 c and summed feature 2 (C 12:0 aldehyde and C 10.928 unknown). Quinone analysis revealed Q-8 as sole respiratory ubiquinone. The genome of TMW 2.2021 T has a size of 4.56 Mb and a G + C content of 38.49 mol%. The ANI value between TMW 2.2021 T and the type strain of closest relative P. iliopiscarium DSM 9896 T was 91.43%. Fingerprinting on the base of M13-RAPD-PCR band pattern and MALDI-TOF MS profiles allowed intraspecies differentiation between our isolates but also supported their distinct lineage to a novel species. Based on phylogenetic, genomic, phenotypic and chemotaxonomic data, strain TMW 2.2021 T and further strains represent a novel species of the genus Photobacterium , for which the name Photobacterium carnosum sp. nov. is proposed. The type strain is TMW 2.2021 T (=DSM 105454 T = CECT 9394 T ). [ABSTRACT FROM AUTHOR]

Photobacterium damselae subsp. piscicida ( Pdp ) is an intracellular fish pathogen that causes photobacteriosis, a disease proven deadly in farmed fish worldwide. This work focuses on the analysis of genome sequences, chromosomes structure and gene contents of two strains from Sparus aurata (DI21) and Solea senegalensis (L091106-03H), isolated on the Spanish Atlantic coast. The comparative genomic analysis revealed that DI21 and L091106-03H share 98% of their genomes, including two virulence plasmids: pPHDP70 encoding siderophore piscibactin synthesis and pPHDP10 encoding the apoptotic toxin AIP56. Both genomes harbour a surprisingly large number of IS elements accounting for 12–17% of the total genome, representing an IS density of 0.15 elements per kb, one of the highest IS density values in a bacterial pathogen. This massive proliferation of ISs is responsible for the generation of a high number of pseudogenes that caused extensive loss of biological functions. Pseudogene formation is one of the main features of Pdp genome that explains most of the ecological and phenotypic differences with respect to its sibling subspecies P. damselae subsp. damselae and to other Vibrionaceae . Evidence was also found proving the existence of two chromosomal configurations depending on the origin of the strains: an European and an Asian/American types of genome organisation, reinforcing the idea of the existence of two geographically-linked clonal lineages in Pdp . In short, our study suggests that the host-dependent lifestyle of Pdp allowed massive IS proliferation and gene decay processes, which are major evolutionary forces in the shaping of the Pdp genome. [ABSTRACT FROM AUTHOR]

Benzophenones (BPs), a group of widely used UV filters, exert multiple, significant toxicity effects. The 11 BPs were selected as target compounds, and the photobacterium acute toxicity test and an index for acute toxicity formation potential (ATFP) were used to evaluate the toxicity variation of BPs before and after a photoinduction–chlorination disinfection process. Orthogonal experiments were performed at different pH values and chlorine dosages. The characteristics of ATFP values for 11 BPs after a photoinduction–chlorination process can be summarized as follows: (1) The ATFPs decreased as the hydroxyl group number increased in BPs molecules. (2) For those BPs with the same hydroxyl group number, the ATFPs were higher when the hydroxyl groups were located at the 3- or 4-position than those at the 2-position; the BPs with hydroxyl groups distributed on two benzene rings had higher ATFPs than those on one ring. (3) Introducing a methoxyl group and sulfonic acid group into BP molecules increased the ATFP values. (4) The ATFPs were pH-dependent, the values of which were lowest at the neutral condition and highest at the acid condition. (5) The ATFPs increased and then decreased as the chlorine dosage increased. The results can be used as a reference to scientifically evaluate the environmental fate and potential risk of BPs in photoinduction–chlorination disinfection processes. [ABSTRACT FROM AUTHOR]

Photobacterium damselae subsp. damselae ( Pdd ) is a marine bacterium that can infect numerous species of marine fish as well as other species including humans. Low iron availability is one of the signs that bacterial pathogens can detect in order to begin colonizing their host, and the reduction of iron levels is a nonspecific host defense strategy that prevents bacterial proliferation. In this work a proteomic approach was used to study the gene expression adaptations of a Pdd strain in response to iron availability. A comparative analysis of induced proteins in both high- and low-iron conditions showed profound cellular metabolic adaptations that result, for instance, in amino acid requirement. It also provided important information about the changes that occur in the energetic metabolism induced by the surrounding iron levels, allowing for the identification of novel potential virulence factors. Among others, genes involved in the synthesis and transport of a vibrioferrin-like siderophore were identified for the first time. In addition to plasmid pPHDD1-encoded Dly and HlyA hemolysins, a pPHDD1-borne operon, which may encode a transferrin receptor, was also found. This operon identification suggests that this virulence plasmid could encode so-far unknown additional virulence factors other than hemolysins. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate seasonal variations (September, December and April) in the initial microbial communities of skin and gills' external mucosal tissues (EMT) and muscle of European plaice (Pleuronectes platessa). Moreover, a potential relationship between EMT and fresh muscle microbiota was examined. The microbial community succession in plaice muscle as a function of fishing season and storage conditions was also investigated. The selected seasons for the storage experiment were September and April. Investigated storage conditions were; fillets packaged in either vacuum or modified atmosphere (70 % CO 2 , 20 % N 2 , 10 % O 2) and chilled/refrigerated conditions (4 °C). Whole fish stored on ice (0 °C) was selected as a commercial standard. Seasonal variations were detected in the initial microbial communities of EMT and plaice muscle. The highest microbial diversity was found in EMT and muscle of April-caught plaice, followed by December and September catch indicating the important role of environmental factors in shaping the initial EMT and muscle microbial communities. The EMT microbial communities were more diverse than fresh muscle samples. The low number of shared taxa between EMT and initial muscle microbial communities indicates that only a minor part of the muscle microbiota came from the EMT. Psychrobacter and Photobacterium were the predominant genera in the EMT microbial communities in all seasons. Photobacterium dominated the initial muscle microbial communities with a gradual seasonal reduction of its abundance from September to April. Storage time and storage conditions shaped a less diverse and distinct community compared to the fresh muscle. However, no clear separation was seen between the communities at the middle and end of storage time. Regardless of EMT microbiota, fishing season and storage conditions, Photobacterium dominated the microbial communities of stored muscle samples. The Photobacterium prevalence as the primary specific spoilage organism (SSO) could be attributed to its high relative abundance in the initial microbiota of muscle and its CO 2 -tolerance. The findings of this study indicate the important contribution of Photobacterium to the microbial spoilage of plaice. Thus, the development of innovative preservation techniques addressing the rapid growth of Photobacterium could contribute to the production of high-quality and shelf-stable convenient retail plaice products. • Initial microbial communities of skin/gills and plaice muscle were varied by season. • Skin/gills had higher microbial diversity than fresh and stored muscle. • A minor part of the initial muscle microbiota came from the skin/gills. • Storage conditions and time shaped a less diverse and distinct community compared to the fresh muscle. • Photobacterium dominated the microbial communities of plaice's muscle. [ABSTRACT FROM AUTHOR]

Bacterial luciferase catalyzes the monooxygenation of long-chain aldehydes such as tetradecanal to the corresponding acid accompanied by light emission with a maximum at 490 nm. In this study even numbered aldehydes with eight, ten, twelve and fourteen carbon atoms were compared with analogs having a double bond at the α,β-position. These α,β-unsaturated aldehydes were synthesized in three steps and were examined as potential substrates in vitro . The luciferase of Photobacterium leiognathi was found to convert these analogs and showed a reduced but significant bioluminescence activity compared to tetradecanal. This study showed the trend that aldehydes, both saturated and unsaturated, with longer chain lengths had higher activity in terms of bioluminescence than shorter chain lengths. The maximal light intensity of ( E )-tetradec-2-enal was approximately half with luciferase of P. leiognathi , compared to tetradecanal. Luciferases of Vibrio harveyi and Aliivibrio fisheri accepted these newly synthesized substrates but light emission dropped drastically compared to saturated aldehydes. The onset and the decay rate of bioluminescence were much slower, when using unsaturated substrates, indicating a kinetic effect. As a result the duration of the light emission is doubled. These results suggest that the substrate scope of bacterial luciferases is broader than previously reported. [ABSTRACT FROM AUTHOR]

The processing environment of salmon processing plants represents a potential major source of bacteria causing spoilage of fresh salmon. In this study, we have identified major contamination routes of important spoilage associated species within the genera Pseudomonas , Shewanella and Photobacterium in pre-rigor processing of salmon. Bacterial counts and culture-independent 16S rRNA gene analysis on salmon fillet from seven processing plants showed higher levels of Pseudomonas spp. and Shewanella spp. in industrially processed fillets compared to salmon processed under strict hygienic conditions. Higher levels of Pseudomonas spp. and Shewanella spp. were found on fillets produced early on the production day compared to later processed fillets. The levels of Photobacterium spp. were not dependent on the processing method or time of processing. In follow-up studies of two plants, bacterial isolates ( n = 2101) from the in-plant processing environments (sanitized equipment/machines and seawater) and from salmon collected at different sites in the production were identified by partial 16S rRNA gene sequencing. Pseudomonas spp. dominated in equipment/machines after sanitation with 72 and 91% of samples from the two plants being Pseudomonas -positive. The phylogenetic analyses, based on partial 16S rRNA gene sequencing, showed 48 unique sequence profiles of Pseudomonas of which two were dominant. Only six profiles were found on both machines and in fillets in both plants. Shewanella spp. were found on machines after sanitation in the slaughter department while Photobacterium spp. were not detected after sanitation in any parts of the plants. Shewanella spp. and Photobacterium spp. were found on salmon in the slaughter departments. Shewanella was frequently present in seawater tanks used for bleeding/short term storage. In conclusion, this study provides new knowledge on the processing environment as a source of contamination of salmon fillets with Pseudomonas spp. and Shewanella spp. , while Photobacterium spp. most likely originate from the live fish and seawater. The study show that strict hygiene during processing is a prerequisite for optimal shelf life of salmon fillets and that about 90% reductions in the initial levels of bacteria on salmon fillets can be obtained using optimal hygienic conditions. [ABSTRACT FROM AUTHOR]

Photobacterium damselae is a well-recognized fish pathogen comprising two subspecies ( damselae and piscicida ) with significant clinical and epidemiological differences. We explored the suitability of MALDI-TOF MS for discriminating P. damselae subspecies in a panel of 45 isolates from diseased fish. MALDI Biotyper approach correctly identified all isolates at species level with average scores values of 2.271 although identification at subspecies level was not reliable. Visual inspection of the spectra using FlexAnalysis revealed five specific peaks ( m / z 4183 and 8367 for subsp. damselae and 4197, 8397 and 8856 for subsp. piscicida ) that may allow their differentiation. A classification model (GA-5A) was constructed based on these peaks using a genetic algorithm (ClinProTools software). Cross-validation and recognition capability values of this model were 100%. Validation of this model was confirmed by blind identification of 21 isolates of both subspecies resulting in sensitivity and specificity values of 100%. This is the first study describing a classification algorithm for MALDI-TOF MS identification of both P. damselae subspecies. This approach proved to be an effective and reliable tool in discriminating within the P. damselae subspecies that might be easily integrated into the workflow of microbiological diagnosis laboratories. Statement of relevance MALDI based tool for differentiation P. damselae subspecies [ABSTRACT FROM AUTHOR]

Bacterial and viral infectious diseases are serious problems in shrimp farming. During the culture of Exopalaemon carinicauda , we found that some individuals showed typical symptoms with pale color for their hepatopancreas, and whitish color for their body, which caused the final mortality of shrimp. In order to know the agent which caused the mortality of shrimp, we isolated the dominant bacteria and analyzed their characteristics. Histopathological observation showed that the tubule lumens of hepatopancreas were enlarged, and the cells located at the hepatopancreatic tubes were damaged severely. Two dominant strains named WH01 and WH02 were isolated from the hepatopancreas of diseased shrimp by thiosulfate citrate bile salt sucrose (TCBS) agar. Analysis on their partial 16S rRNA sequences showed that WH01 and WH02 had the highest similarity with Photobacterium damselae subsp. damselae . Furthermore, a specific molecular methodology (using toxR gene) and Biolog system phenotypic analysis confirmed that WH01 and WH02 were two strains of Photobacterium damselae subsp. damselae . Hemolysis test showed that both WH01 and WH02 strains could cause beta hemolysis on sheep blood agar plates. Artificial infection test revealed that both WH01 and WH02 could infect the shrimp E. carinicauda and lead to 100% mortality. The median lethal dose (LD 50 ) for WH01 was 2.30 × 10 5 CFU/g (body weight) and the LD 50 for WH02 was 1.09 × 10 5 CFU/g (body weight). In addition, these two strains could also infect the shrimp Litopenaeus vannamei to cause its mortality by intramuscular injection. These data indicated that Photobacterium might be a common pathogen of shrimps. The pathogenicity of Photobacterium to shrimp must be paid more attention for shrimp farming. [ABSTRACT FROM AUTHOR]

The marine fish pathogen Photobacterium damselae subsp. piscicida ( Phdp ) is responsible for important disease outbreaks affecting cultured fish species including the flatfish Solea senegalensis . In the present work, transcription of iron metabolism related genes (TF, FERR-M, HP-1 and HAMP-1) as well as innate immune system components such as complement proteins (C3 and C7), lysozyme (LYS-G), TNF family (TNFα, TRAF-3), NCCRP-1 and heat shock protein encoding genes (HSP70, HSP90AA, HSP90AB and GP96) has been determined in the liver and kidney of S. senegalensis specimens after Phdp infection. Intraperitoneal injection (IP) and immersion (IM) routes have been used for infection. Fish developed specific antibodies in both cases, higher levels being detected in IP infected specimens. Both infection routes resulted in increased relative transcript levels of FERR-M, HP-1 and HAMP-1 genes and TF decreased relative transcription, conducting to lower iron availability for the pathogen. This response can be considered as a strategy to limit iron availability for Phdp , a pathogen capable to obtain iron from transferrin. Relative transcription of genes encoding lysozyme and complement factors C3 and C7 were also increased regardless the infection route; the liver was the main organ involved in the initial stages and the kidney in later stages of the infection. TNFα and TRAF-3 relative gene transcription increased 24 h post-infection. TRAF-3 gene induction was detected 30 d post-infection, whilst no changes in TNFα were observed 72 h or 30 d post-infection. NCCRP-1 changes were observed after IP infection in the liver and kidney; however, IM infection resulted only in slight changes in the kidney of infected fish. This different response observed maybe related to a lower number of invaded cells by the pathogen. Finally, changes in HSP90AB and GP96 have been detected after infection by both routes. Different late modulation has been observed in assayed genes depending on the route of infection. Thus, only LYS-G, TF, NCCRP-1, GP96 and HSP90AB gene transcription was modulated 30 d post-infection in the kidney of IM infected specimens; however, IP infected fish showed modulation in a higher number of genes both in liver and kidney tissues. The implications of these responses in resistance to infection by Phdp need to be elucidated. [ABSTRACT FROM AUTHOR]

Benzophenones compounds (BPs) are widely used as UV filters, and have been frequently found in multiple environmental matrices. The residual of BPs in water would cause potential threats on ecological safety and human health. Chlorination disinfection is necessary in water treatment process, in which many chemicals remained in water would react with disinfectant chlorine and form toxic by-products. By using ultra performance liquid phase chromatography quadrupole time of flight mass spectrometer (UPLC-QTOF-MS), nuclear magnetic resonance (NMR), the transformation of 4-hydroxyl benezophenone (4HB) with free available chlorine (FAC) was characterized. Eight major products were detected and seven of them were identified. Transformation pathways of 4HB under acid, neutral, and alkaline conditions were proposed respectively. The transformation mechanisms involved electrophilic chlorine substitution of 4HB, Baeyer-Villiger oxidation of ketones, hydrolysis of esters and oxidative breakage of benzene ring. The orthogonal experiments of pH and dosages of disinfectant chlorine were conducted. The results suggested that pH conditions determined the occurrence of reaction types, and the dosages of disinfectant chlorine affected the extent of reactions. Photobacterium assay demonstrated that acute toxicity had significant increase after chlorination disinfection of 4HB. It was proved that 3,5-dichloro-4HB, one of the major transformation products, was responsible for the increasing acute toxicity after chlorination. It is notable that, 4HB at low level in real ambient water matrices could be transformed during simulated chlorination disinfection practice. Especially, two major products 3-chloro-4HB and 3,5-dichloro-4HB were detected out, implying the potential ecological risk after chlorination disinfection of 4HB. [ABSTRACT FROM AUTHOR]

Photodynamic antimicrobial chemotherapy (PACT), as one of the promising alternative antimicrobial treatment, has received great attention in recent years. In this work, a new antimicrobial material has been elaborated by grafting a neutral porphyrin, the metallated 5-(4-azidophenyl)-10,15,20-triphenylporphyrin, onto lignocellulosic fibers by using the Copper (I)-Catalyzed Alkyne-Azide 1,3-dipolar Cycloaddition (CuAAC) reaction. The cross-linked porphyrin-Kraft pulp material was characterized by infrared and by XPS spectroscopy analyses, which proved the covalent linkage between the porphyrin and propargylated Kraft pulp fibers. The antimicrobial activity of this material was tested under visible light irradiation with a low light dose (9.5 J/cm 2 ) against Staphylococcus aureus and Pseudomonas aeruginosa. The two bacterial strains deposited on the resulting photosensitizing Kraft pulp are efficiently killed after illumination. Such materials could find applications in industrial, household and medical environments as an alternative to overcome the widespread microbial multiresistance to classical treatments. [ABSTRACT FROM AUTHOR]

The present work aims at demonstrating the application of UV/S 2 O 8 2 − system successfully for degradation of cetirizine dihydrochloride (CTZ) from aqueous waste. More than 95% CTZ was degraded within 90 min of UV irradiation. The degradation kinetics followed a pseudo-first order kinetics at all the experimental conditions studied. The studied process enhanced the biodegradability, BOD 5 /COD ratio from 0.15 to 1.94 of the aqueous wastewater. Acute toxicity test using Photobacterium phosphoreum showed that the degradation products are less toxic than the initial toxicity levels of CTZ. The sulfate radical generated from the photochemical decomposition of S 2 O 8 2 − shows that UV/S 2 O 8 2 − system is a kinetically favorable process in removing cetirizine hydrochloride from aqueous waste along with reduction of toxicity. [ABSTRACT FROM AUTHOR]

A β-galactoside α2,6-sialyltransferase (ST) from the marine bacterium Photobacterium sp. JT-ISH-224 with a broad acceptor substrate specificity was fused to a fungal biotin-binding protein tamavidin 2 (TM2) to produce immobilized enzyme. Specifically, a gene for the fusion protein, in which ST from Photobacterium sp. JT-ISH-224 and TM2 were connected via a peptide linker (ST-L-TM2) was constructed and expressed in Escherichia coli . The ST-L-TM2 was produced in the soluble form with a yield of approximately 15,000 unit/300 ml of the E. coli culture. The ST-L-TM2 was partially purified and part of it was immobilized onto biotin-bearing magnetic microbeads. The immobilized ST-L-TM2 onto microbeads could be used at least seven consecutive reaction cycles with no observed decrease in enzymatic activity. In addition, the optimum pH and temperature of the immobilized enzyme were changed compared to those of a free form of the ST. Considering these results, it was strongly expected that the immobilized ST-L-TM2 was a promising tool for the production of various kind of sialoligosaccharides. [ABSTRACT FROM AUTHOR]

This paper focuses on the degradation of Thiamethoxam (THIA) in aqueous solution by ozonation. Four influencing factors: pH, THIA initial concentration, ozone concentration and temperature were investigated in order to optimize the conditions, and pH showed the greatest impact; the removal efficiency reached up to 71.19% under the condition of pH 5–11, THIA initial concentration 50–300 mg L −1 , the ozone concentration 10–22.5 mg L −1 at 293–308 K after 90 min. Four main intermediates were separated and identified and the possible degradation mechanism was proposed. The luminous intensity of photobacteria and the chemical oxygen demand (COD) were measured to assess the changes of toxicity and mineralization in ozonation process, and results showed that the inhibition rate decreased by 60% and 76% of COD was removed after 180 min with the THIA initial concentration was 200 mg L −1 . Our study powerfully demonstrates that the degradation of THIA in aqueous solution by ozonation is a promising technology. [ABSTRACT FROM AUTHOR]

The lux -operon of bioluminescent bacteria contains the genes coding for the enzymes required for light emission. Some species of Photobacteria feature an additional gene, luxF , which shows similarity to luxA and luxB , the genes encoding the heterodimeric luciferase. Isolated dimeric LuxF binds four molecules of an unusually derivatized flavin, i.e., 6-(3′-( R )-myristyl)-FMN (myrFMN). In the present study we have heterologously expressed LuxF in Escherichia coli BL21 in order to advance our understanding of the protein's binding properties and its role in photobacterial bioluminescence. Structure determination by X-ray crystallography confirmed that apo-LuxF possesses four preorganized binding sites, which are further optimized by adjusting the orientation of amino acid side chains. To investigate the binding properties of recombinant LuxF we have isolated myrFMN from Photobacterium leiognathi S1. We found that LuxF binds myrFMN tightly with a dissociation constant of 80 ± 20 nM demonstrating that the purified apo-form of LuxF is fully competent in myrFMN binding. In contrast to LuxF, binding of myrFMN to luciferase is much weaker ( K d = 4.0 ± 0.4 μM) enabling LuxF to prevent inhibition of the enzyme by scavenging myrFMN. Moreover, we have used apo-LuxF to demonstrate that myrFMN occurs in all Photobacteria tested, irrespective of the presence of luxF indicating that LuxF is not required for myrFMN biosynthesis. [ABSTRACT FROM AUTHOR]

Recent developments in detection and enumeration of histamine-producing bacteria (HPB) have created powerful molecular-based tools to better understand the presence of spoilage bacteria and conditions, resulting in increased risk of scombrotoxin fish poisoning. We examined 235 scombrotoxin-forming fish from the Gulf of Mexico for the presence of high HPB. Photobacterium damselae subsp. damselae was the most prevalent HPB (49%), followed by Morganella morganii (14%), Enterobacter aerogenes (4%), and Raoultella planticola (3%). The growth characteristics and histamine production capabilities of the two most prevalent HPB were further examined. M. morganii and P. damselae had optimum growth at 35°C and 30 to 35°C and 0 to 2% and 1 to 3% NaCl, respectively. P. damselae produced significantly (P < 0.001) higher histamine than M. morganii in inoculated mahimahi and Spanish mackerel incubated at 30°C for 24 h, but histamine production was not significantly different between the two HPB in inoculated tuna, possibly due to differences in muscle composition and salt content. Results in this study showed that P. damselae was the most prevalent high HPB in Gulf of Mexico fish. In addition, previously reported results using the traditional Niven's method may underreport the prevalence of P. damselae. Molecular-based methods should be used in addition to culture-based methods to enhance detection and enumeration of HPB. [ABSTRACT FROM AUTHOR]

Outbreaks of histamine-related food poisoning are mainly caused when histidine-rich red fish are not preserved at an optimal temperature, which triggers the bacterial production of histamines. However, it has been found that food poisoning occurs even when the temperature is managed by refrigeration, thus drawing our attention to the histamine-producing bacteria, which can proliferate at lower temperatures. In the present study, we investigated the effects of environmental factors (temperature and pH) on the histamine production of the psychrophilic bacterial species, Photobacterium iliopiscarium . The results of culturing this bacterium in a histidine broth suggested that there was a risk of histamine food poisoning at all of the investigated culturing temperatures (5 °C, 10 °C, and 20 °C). The amount of histamine produced exceeded 500 ppm after a certain period, and high levels of histamine were produced at low pH. Moreover, this trend was also seen in the level of expression of the hdcA gene. The present study suggests that the risk of bacterial food poisoning is particularly high in low-pH food products. [ABSTRACT FROM AUTHOR]

In order to improve the catalytic efficiency of recombinant Photobacterium sp. JT-ISH-224 α2–6-sialyltransferase Psp2,6ST(15–501)-His 6 in sialylating α-GalNAc-containing acceptors for the synthesis of tumor-associated carbohydrate antigens sialyl Tn (STn), protein crystal structure-based mutagenesis studies were carried out. Among several mutants obtained by altering the residues close to the acceptor substrate binding pocket, mutant A366G was shown to improve the sialyltransferase activity of Psp2,6ST(15–501)-His 6 toward α-GalNAc-containing acceptors by 21–115% without significantly affecting its sialylation activity to β-galactosides. Furthermore, the expression level was improved from 18–40 mg L −1 for the wild-type enzyme to 72–110 mg L −1 for the A366G mutant. In situ generation of CMP-sialic acid in a one-pot two-enzyme system was shown effective in overcoming the high donor hydrolysis of the enzyme. Mutant A366G performed better than the wild-type Psp2,6ST(15–501)-His 6 for synthesizing Neu5Acα2–6GalNAcαOSer/Thr STn antigens. [ABSTRACT FROM AUTHOR]

Photobacterium sp. TLY01, a novel strain of Photobacterium genus isolated from an oil field, was found to allow the accumulation of polyhydroxyalkanoates (PHAs) from a series of sustainable substrates, including glycerol, carbohydrates, plant oils, and volatile fatty acids. Interestingly, Photobacterium sp. TLY01 could effectively utilize plant oils or corn starch to synthesize poly-3-hydroxybutyrate (PHB). When propionate or valerate was added as secondary carbon source, poly(3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) was produced. In fed-batch fermentation, the strain produced 53.89 g/L PHB using glycerol. When soybean oil and valerate were used as joint substrates, PHBV titer reached 16.28 g/L in bioreactor cultures. Furtherly, tryptone and yeast extract in culture medium were replaced with corn steep liquor to support PHA production. At last, a mixed substrate containing waste cooking oil, corn starch, and valerate was employed for PHBV production, achieving a titer of 4.01 g/L. The results indicated that Photobacterium sp. TLY01 is a promising strain for PHA production with low-cost sustainable substrates. [Display omitted] • A novel strain of Photobacterium sp. TLY01 was employed to produce PHA. • Photobacterium sp. TLY01 could directly utilize corn starch. • PHB titer reached 53.89 g/L using glycerol in fed-batch fermentation. • The strain produced 16.28 g/L PHBV using soybean oil/valerate in bioreactor cultures. [ABSTRACT FROM AUTHOR]

Photobacterium damselae subsp. piscicida ( Pdp ) kills many cultured marine fish. As it evolves resistance to existing vaccines, new vaccines are needed. PPA1 is a major antigenic protein of Pdp . Here, DNA vaccines encoding wild-type PPA1 (pPPA1 wt ) and codon-optimized PPA1 (pPPA1 opt ) were constructed and tested against Pdp in Japanese flounder. The mRNA levels of the two antigenic genes at the vaccination site were not different, but the protein level was significantly higher in the pPPA1 opt -vaccinated fish. In addition, after a bacterial challenge, the levels of interleukin (IL)-1β, IL-6 and IFN-γ mRNA significantly increased in the pPPA1 opt -vaccinated fish but not in the pPPA1 wt -vaccinated fish. The relative percent survival (RPS) after the challenge was higher in the pPPA1 opt -vaccinated fish (90.9) than in the pPPA1 wt -vaccinated fish (69.2). At the early stage of the infection after the challenge, the number of viable Pdp in the spleen was significantly lower in the pPPA1 opt -vaccinated fish than in the pPPA1 wt -vaccinated fish. These data show that codon-optimized DNA vaccine pPPA1 opt had a strong immunogenicity and conferred protective efficacy against Pdp infection in Japanese flounder. [ABSTRACT FROM AUTHOR]

Photobacterium damselae subspecies damselae and piscicida are known fish pathogens responsible for disease outbreaks in several cultured fish species. Fast detection of these pathogens is important for management and control of disease outbreaks. In this study, we developed a molecular approach for quantification of P. damselae species and detection of its subspecies ( piscicida and damselae ) based on real time PCR (RT-PCR) and PCR-denaturing gradient gel electrophoresis (PCR-DGGE) of toxR gene fragments. In addition, the efficacy of this molecular methodology was tested against water samples from a natural environment (Ria de Aveiro estuary, Aveiro, Portugal) and from an intensive recirculating aquaculture system (RAS). In the first phase of this study we developed a RT-PCR targeting the toxR gene suitable for detection and quantification of P. damselae species. After the first RT-PCR trial, a nested PCR-DGGE was developed to determine the presence of P. damselae subspecies in the positive samples. Confirmation of the identity of different subspecies was obtained by Sanger DNA sequencing and phylogenetic analysis of toxR gene fragments obtained from excised DGGE bands. Our RT-PCR analysis detected between 1797.85 ± 376.15 (ca 0.71 fg) and 2976.68 ± 1253.63 (ca 1.76 fg) gene copy numbers of P. damselae toxR genes in the aquaculture samples. The DGGE analysis of these samples detected two equally abundant bands near the DGGE reference position for P. damselae subsp. piscicida. The sequence and phylogeny analyses of excised bands revealed the presence of two populations with distinct toxR gene sequences suggesting a close phylogenetic relationship with P. damselae subsp. piscicida . Contrary to aquaculture samples, no RT-PCR signal was obtained for DNA extracted from estuarine water samples. Here we provide evidences that the molecular methodology developed in this study can be used for overall quantification of P. damselae and subsequent detection of its subspecies in natural ecosystems and aquaculture systems. [ABSTRACT FROM AUTHOR]

Photobacteriosis and streptococcosis are the most threatening diseases in cage-cultured cobia, Rachycentron canadum , due to high mortality of 50–80% and annual outbreaks in Taiwan. Garlic, Allium sativum , has long been known to have broad antibacterial properties. This study aimed to examine the in vitro antibacterial activities of garlic and the effects of dietary garlic on disease resistance against Photobacterium damselae subsp. piscicida and Streptococcus iniae and on growth in cobia. The results revealed the marked inhibitory effect of garlic against both P. damselae subsp. piscicida and S. iniae , and feeding garlic diet significantly conferred resistance to challenge with P. damselae subsp. piscicida or/and S. iniae . Cobia fed garlic powder at doses of 0.5 and 1.5 g/kg b.w. for 28 days produced significantly (p < 0.05) lower mortality after a challenge with P. damselae subsp. piscicida and higher percent weight gain. Cobia fed garlic powder at a dose of 1.2 g/kg b.w. for 21 days and at doses of 0.4 and 1.2 g/kg b.w. for 28 days provided significant (p < 0.01) resistance against S. iniae infection. A diet containing garlic powder at a dose of 1.2 g/kg b.w. for 28 days provided significant (p < 0.05) protection against P. damselae subsp. piscicida plus S. iniae combined infection in cobia. [ABSTRACT FROM AUTHOR]

Sea bass were experimentally infected with Listonella anguillarum or Photobacterium damselae subsp. piscicida ( Phdp ). At 24 and 72 h post-infection, the expression analysis of immune-relevant genes (IL-1β, IL-6, IL-8, Hepcidin), the transcriptional level and detection of HSP70, and the quantification of serum iron were investigated in association with the histological analysis and the bacterial recognition in tissues by immunohistochemistry. At 15 days post-infection, the specific antibody response was detected in surviving fish, as well as the transcriptional levels of TcR and BcR sequences. Both experimental infections were characterized by a similar acute response, whereas different histological and immunohistochemistry evidences were observed. In particular, the early reaction appeared suitable for the clearance of L. anguillarum , thus limiting the histological lesions, the bacterial dissemination and the further development of acquired immunity in surviving fish. On the contrary, the innate response appeared not enough to resolve the Phdp infection, which was characterized by tissue damage, bacterial widespread and substantial detection of specific humoral immunity in surviving fish, also associated to lymphocytes clonal expansion. Besides the opportunistic conditions involved in fish vibriosis and pasteurellosis, the comparison between these experimental infection models seems to suggest that the rate of development of the acquired immunity is strictly linked to the activation of the host innate response combined to the degree of bacterial virulence. [ABSTRACT FROM AUTHOR]