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【Objective】The causative agent was isolated from the diseased Micropterus salmoides tissue. The physiological properties of the pathogenic bacteria were identified, and their virulence genes and drug resistance genes were analyzed, with an aim to provide guidance for the scientific use of drugs in clinical practice.【Method】Samples were collected from pathologic tissues of diseased M. salmoides from a fish breeding factory in Zhanjiang, Guangdong Province, China. The bacteria were isolated by dilution coating method, the 16S rRNA sequence comparison and biochemical tests were performed to identify the species, and the virulence genes, drug resistance genes and drug sensitivity characteristics were also identified.【Result】Bacteria with round colony morphology, smooth milky white surface and opaque color were isolated from pathologic tissues of M. salmoides, and numbered as MSB-2, which was identified as Aeromonas in Gram-negative bacteria through phenotypic identification by Gram staining and physiological and biochemical reactions. By amplifying the 16S rRNA gene sequence and constructing a phylogenetic tree, the bacterium was further identified as A. veronii. The strain had virulence-related genes such as act, aer and aexT and resistance-related genes such as tetC, tetA and sull. The results of the drug sensitivity test showed that the bacterium was sensitive to carbenicillin, doxycycline, cefalexin, neomycin, gentamicin, cefradine, minocycline, cefazolin and etc. Artificial regression of healthy M. salmoides infected with A. veronii showing clinical signs similar to those of diseased fish, which were the same as those of the naturally occurring disease, such as congestion of the ventral and pectoral fin bases, redness and swelling of the anus, and obvious enlargement of the abdomen, etc. And a large amount of fluid in the abdominal cavity was found by autopsy.【Conclusion】The above results indicate that A. veronii is the pathogenic bacterium causing this disease of M. salmoides, and the approved fishery drugs such as neomycin and doxycycline can be used to control the disease during the breeding process.

Abstract The JN.1 variant of COVID‐19 has emerged as the dominant strain worldwide since the end of 2023. As a subclade of the BA.2.86 variant, JN.1 harbors a unique combination of mutations inherited from the BA.2.86 lineage, notably featuring the novel L455S mutation within its receptor‐binding motif. This mutation has been linked to increased transmissibility and enhanced immune evasion capabilities. During the rise of JN.1, evidence of resistance to various monoclonal antibodies and reduced cross‐neutralization effects of the XBB.1.5 vaccine have been observed. Although the public health threat posed by the JN.1 variant appears relatively low, concerns persist regarding its evolutionary trajectory under immune pressure. This review provides a comprehensive overview of the evolving JN.1 variant, highlighting the need for continuous monitoring and investigation of new variants that could lead to widespread infection. It assesses the efficacy of current vaccines and therapeutics against emerging variants, particularly focusing on immunocompromised populations. Additionally, this review summarizes potential vaccine advancements and clinical treatments for COVID‐19, offering insights to optimize prevention and treatment strategies. This review thoroughly evaluates the JN.1 variant's impact on public health and its implications for future vaccine and therapeutic development, contributing to ongoing efforts to mitigate the risk of virus transmission and disease severity.

Caspase-8, a member of the caspase family, is an initiating caspase and plays a crucial role in apoptosis. In this study, the full-length cDNA of caspase8-like (CASP8-like) was isolated from Crassostrea hongkongensis (C. hongkongensis) by RACE-PCR. ChCASP8-like contained a 1599-bp open reading frame (ORF) encoding 533 amino acids with two conserved death effector domains (DEDs) and a cysteine aspartase cysteine structural domain (CASc). Amino acid sequence comparison showed that ChCASP8-like shared the highest identity (85.4%) with CASP8-like of C. angulata. The tissue expression profile showed that ChCASP8-like was constitutively expressed in gills, hepatopancreas, mantle, adductor muscle, hemocytes and gonads, and was significantly upregulated in hemocytes, hepatopancreas and gills under hyper-salinity stress. The apoptosis-related genes, including ATR, CHK1, BCL-XL, CASP8-like, CASP9 and CASP3, were significantly activated by hyper-salinity stress, but were remarkably inhibited by ChCASP8-like silencing. The caspase 8 activity was increased by 1.7-fold after hyper-salinity stress, and was inhibited by 9.4% by ChCASP8-like silencing. Moreover, ChCASP8-like silencing clearly alleviated the apoptosis resulting from hyper-salinity stress. These results collectively demonstrated that ChCASP8-like played a crucial role in inducing apoptosis against hyper-salinity stress.

Measurement(s) whole genome sequencing Technology Type(s) Illumina Sequencing • Oxford Nanopore Sequencing

Interleukin-15 (IL15) is a proinflammatory cytokine that could induce the production of inflammatory cytokines. In this study, the α chain of the IL15 receptor of Epinephelus coioides (Ec-IL15Rα), a natural regulator of IL15, was identified, and immune response functions of fish were determined and characterized. Ec-IL15Rα contains a 720 bp open reading frame that encodes 239 amino acids, including four typical conserved cysteine residues with a highly conserved sushi domain. Ec-IL15Rα is closely related to Epinephelus lanceolatus and is the most clustered with teleost. Subcellular localization studies showed that Ec-IL15Rα was situated in the cytoplasm and cell membrane. Ec-IL15Rα was detected in 11 tissues, with the highest expression in the liver and blood. Meanwhile, the Ec-IL15Rα transcriptional levels substantially increased in nine tissues after Vibrio harveyi infection. Ec-IL15Rα was significantly up-regulated in HKLs by ConA, PHA, LPS and poly I:C stimulation. In vitro analysis, the recombinant protein of rEc-IL15Rα stimulates HKL proliferation and IL1R, IL6R, IL10, and IL16 expression. Challenge experiments revealed that IL15Rα protein showed an increase of 6.67–10% survival protection rate after V. harveyi infection. This study provides a better understanding of the immune protection of IL15Rα in vertebrate fish.

In previous studies, natural killer lysin (NK-lysin) emerged as a crucial antimicrobial peptide (AMP) discharged by NK cells and CTLs. The sequence of NK-lysin was cloned and discovered in some fishes, but its function remains unclear. In our study, we obtained a copy of NK-lysin from the spleen of the healthy clownfish (Amphiprion ocellaris; AoNK-lysin) through cloning and proceeded to investigate its potential functions and activities. The findings showed that the AoNK-lysin gene’s open reading frame (ORF) had a length of 465 base pairs (bp) and encoded 154 amino acids (aa), which included a saposin B domain and six cysteine residues that are highly conserved, forming three intrachain disulfide bonds to carry out antimicrobial activity. The AoNK-lysin gene was widely present in different tissues, with the skin showing the highest expression, followed by the eye, intestine, and muscle. Additionally, the expression of AoNK-lysin was significantly upregulated in the immune organs (spleen, gill, intestine, and head kidney) of A. ocellaris after being challenged by Singapore group iridovirus (SGIV). Furthermore, a 399 base pair cDNA sequence that encodes the fully developed peptide of AoNK-lysin was successfully inserted into a secretion plasmid called pPIC9K. Subsequently, a significant amount of the recombinant AoNK-lysin protein was efficiently manufactured using the Pichia pastoris expression system. The antibacterial test demonstrated that the AoNK-lysin protein significantly suppressed the growth of various pathogens, particularly Streptococcus agalactiae, Streptococcus iniae, Salmonella typhi, Shigella sonnei, Pseudomonas aeruginosa, and Aeromonas caviae. The minimal inhibitory concentration (MIC) was found to be 7.81 μg/mL. Further analysis of antiviral assays showed all the viral mRNA of SGIV to be significantly reduced after AoNK-lysin protein stimuli in FHM cells. Collectively, these discoveries indicate that AoNK-lysin exhibits features of both direct pathogen-killing abilities and inhibited virus replication.

Little is known about the effects of oxytetracycline (OTC) on marine fish. Using juvenile pearl gentian grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂), we investigated the effects of 56 days dietary oxytetracycline (OTC; OTCD) exposure (80 mg/kg body weight/day) on fish growth performance, intestinal health and antibiotic residue. Meanwhile, the alteration of intestinal health status and antibiotic residue after 7 (O7) or 14 days (O14) OTC withdrawal treatment were explored. We also assessed the potential human health risks based on target hazard quotient (THQ). The results showed that OTC exposure had no effects on growth rate parameters but caused liver and intestine atrophy. OTC exposure impaired the intestinal health by distorting intestinal morphological features, inducing oxidative stress, repressing immune function, triggering NF-κB-mediated inflammatory response and apoptosis, while 7 days OTC withdrawal treatment improved intestinal health status and 14 days OTC withdrawal treatment further improved it. In addition, the order of OTC residue in tested tissues after OTC exposure was: liver > kidney > spleen > muscle > intestine. OTC residue was significantly decreased in all tissues along with the increasing of withdrawal treatment period. Adults and children consuming the edible tissues (muscle) of OTC-treated or withdrawal-treated pearl gentian grouper would not experience any previous health risk as the THQ

Offshore industries and resources are the links between humans and the marine ecosystem. Several risk factors are associated with beach activities. The risk of Vibrio infection at bathing beaches is often overlooked as there are virtually no regulations regarding them. In this study, we investigated the current prevalence of pathogenic Vibrio spp. on the main beaches of Shenzhen. The risk indicator levels of pathogenic Vibrio species obtained were analyzed using 17 virulence genes mainly associated with Vibrio species and are responsible for several ailments and infections. A total of 60 Vibrio strains were isolated and identified by morphological observation, evolutionary tree alignment, and biochemical testing. There was a high abundance of Vibrio in the seawater. Also, a positive correlation was observed between the presence of virulence genes and the exhibition of high pathogenicity after artificially infecting fish with some of the virulent Vibrio species. In the infection experiment, it was observed that all the zebrafish infected with MEDF7 (Vibrio alginolyticus) and JSW-YELLOW (Vibrio harveyi) died a day after injection, with varying degrees of abdominal enlargement and skin ulceration. The mortality rates for strains with medium risk and low risk were 65% and 45%, respectively. Lethal dose 50 (LD50) values were 5.67 ×104 CFU/fish, 3.72 ×105 CFU/fish, and 4.31 ×105 CFU/fish for the high-risk, medium-risk, and low-risk strains of zebrafish, respectively. The results of the antibiotic sensitivity test showed that all the six experimental strains, except JSW-YELLOW, were resistant to doxycycline and neopenicillin. In summary, our study first identified and evaluated the pathogenicity of Vibrio in the Shenzhen beach baths, serving as a scientific benchmark for Vibrio risk prevention and control as well as guidance for Vibrio diagnosis through virulence factor detection and risk classification.

Fish nocardiosis is a chronic, systemic, granulomatous disease in aquaculture. Nocardia seriolae has been reported to be one of the main pathogenic bacteria of fish nocardiosis. There are few studies on the associated virulence factors and pathogenesis of N. seriolae. Alanine dehydrogenase (ALD), which may be a secreted protein, was discovered by analysis using bioinformatics methods throughout the whole genomic sequence of N. seriolae. Nevertheless, the roles of ALD and its homologs in the pathogenesis of N. seriolae are not demonstrated. In this study, the function of N. seriolae ALD (NsALD) was preliminarily investigated by gene cloning, host cell subcellular localization, secreted protein identification, and cell apoptosis detection. Identification of the extracellular products of N. seriolae via mass spectrometry (MS) analysis revealed that NsALD is a secreted protein. In addition, subcellular localization of NsALD-GFP recombinant protein in fathead minnow (FHM) cells showed that the strong green fluorescence co-localized with the mitochondria. Moreover, apoptosis assays demonstrated that the overexpression of NsALD induces apoptosis in FHM cells. This study may lay the foundation for further exploration of the function of NsALD and facilitate further understanding of the pathogenic mechanism and the associated virulence factors of N. seriolae.

Galectin is a kind of lectin that can promote the cell adhesion, proliferation, and phagocytosis and participates in immune regulation and destruction of microbes. In this study, a galectin-related protein (On-GRP) homolog was identified from Nile tilapia, and its expression level and antibacterial ability were studied. The Open Reading Frame, which encoded a 179 amino acid protein (GenBank accession no: XM_005733705.1), was 537 bp. The On-GRP possessed a carbohydrate recognition domain. qRT-PCR showed that the On-GRP was detected in the examined tissues in healthy Nile tilapia, and the highest expression levels was observed in the skin. After challenge with Streptococcus agalactiae, the On-GRP expression was up-regulated significantly (P < 0.05) in the whole blood, head kidney, gills and thymus. In addition, the recombinant On-GRP (rOn-GRP) could agglutinate and bind Streptococcus agalactiae and Aeromonas hydrophila. In vitro and in vivo bacteriostatic tests showed that the rOn-GRP could inhibit the growth of bacteria. Besides, the rOn-GRP could promote the phagocytic ability of macrophages to engulf bacteria. Over all, this study indicated On-GRP is involved in the immune responses of Nile tilapia against bacterial pathogens.

Disease is a significant constraint faced by aquaculture, and its prevention and control bring together a hub of recent research. Several resources and resorts have been applied to prevent diseases in aquaculture. Probiotics are known to be beneficial natural derivatives that have several benefits in aquaculture. Currently, several commercial probiotics are used in the aquaculture industry that contains one or more live microorganisms. In the aquaculture industry, Bacillus species is one of the most widely used probiotic organisms. They are considered distinctive and are found to be natural members of the gut microbiota of some fish species. The safety of beneficial microorganisms is essential since some of these organisms are reported to harbor traits that might be transferable to their hosts. In this study, the safety of some Bacillus-based commercial probiotics used in aquaculture in terms of virulence and drug resistance were assessed. Commercial Bacillus species after isolation were screened for the presence of virulence genes (nheA, nheB, nheC, hblA, hblC, hblD, cytK, and entFM) and one emetic gene (ces), as well as their resistance to some antibiotics. Most isolates did not possess any of the virulence genes assessed. Nonetheless, three isolates harbored the nheABC and entFM enterotoxin genes, while two had the hblA, hblC, hblD, cytK genes. None of the isolates possessed the ces emetic gene. Antibiotic resistance assessment revealed most of the isolates to be resistant to β-lactam antibiotics, including penicillin, ampicillin, oxacillin, cefuroxime, and ceftriaxone, and also to minocycline.

The teleost non-specific cytotoxic cell (NCC), as the evolutionary precursors of NK cells, is an important cytotoxic cell population in the innate immune system of teleost. We have recently realized that costimulatory CD80/86 have conservation in structural and interactional features with its ligand CD28 in Nile tilapia (Oreochromis niloticus). However, the ability of CD80/86 to regulate NCC activity has not been fully investigated. In the present study, we first obtained the recombinant fusion CD80/86 protein from O. niloticus (rOn-CD80/86). Then, NCC incubation with rOn-CD80/86 resulted in a significant production of NCC effector cytokines, including tumor necrosis factor-alpha, cellular apoptosis susceptibility and NK-lysin. Furthermore, NCC treatment with rOn-CD80/86 could significantly improve the ability to kill kidney cells of Grass carp (CIK) and up-regulate the activities of caspase-1 and caspase-3 in CIKs. The yeast, two-hybrid assay showed that On-CD80/86 cannot directly interact with non-specific cytotoxic cell receptor protein-1 of O. niloticus (On-NCCRP-1). The single-cell RNA-Seq data of Nile tilapia head kidney lymphocytes analysis found On-CD28 did not exhibit expression on NCCs subsets. The above results suggest that costimulatory molecules On-CD80/86 is independent of On-NCCRP-1 and On-CD28 receptor in modulating NCC killing activity in vitro of Nile tilapia. The results also provide more insights into the mechanism of NCC activity regulation.

CD96 is one of the immune superfamily members and it is identified as a T cell-specific receptor. In this study, we cloned a CD96 from Nile tilapia (Oreochromis niloticus, named OnCD96). The open reading frame of OnCD96was 1371 bp, encoding a protein of 456 amino acids. Sequence alignment analysis indicated that OnCD96 contained two Ig-like domains in entodomain, proline-rich motif, and ITIM motif in the cytoplasm. Subcellular localization studies showed that OnCD96 was distributed mainly in the cytoplasm and on the cytoplasmic membrane. In healthy tilapia, OnCD96 was distributed in all the tested tissues and relatively higher in the liver. After Streptococcus agalactiae infection, the expression of OnCD96 in the thymus, brain, and spleen reached its peak at 72 h, 48 h, and 24 h, respectively. After stimulation with poly I:C, the expression of OnCD96 in thymus and spleen reached its peak at 6 h and 24 h respectively. While, the expression in the brain had double peaks, which were at 24 h and 96 h. After stimulation with Keyhole limpet hemocyanin (KLH), a classical T cell-dependent antigen, the expression of OnCD96 was significantly up-regulated in blood and head kidney. Moreover, compared with the first challenge, OnCD96 was up-regulated earlier after the second challenge. Yeast two-hybrid assay indicated that there might be interaction between OnCD96 and OnNecl5. These results suggested that OnCD96 plays an important role during pathogens infection, and the interaction between CD96 and Necl5 is conserved in Nile tilapia.

Peptidoglycan recognition proteins (PGRPs) are a family of pattern recognition receptors (PRRs) mediating the recognition of peptidoglycan. In the present study, a short-type PGRP gene named Eco-PGRP-S was identified in the orange-spotted grouper (Epinephelus coioides), a major commercial marine fish cultured in Asia. Eco-PGRP-S gene was constitutively expressed in all tissues examined, with the highest expression level observed in gill and skin. As a typical PRR, Eco-PGRP-S is inducible following the stimulation of peptidoglycan, and has an ability to bind peptidoglycan. Importantly, Eco-PGRP-S has been proven to have Zn2+-dependent amidase activity and direct antibacterial activity against Vibrio Harveri and Edwardsiella tarda. In addition, Eco-PGRP-S is mainly localized in cytoplasm and nucleus, and is able to significantly trigger the activation of NF-κB signalling. The present research thus contributes to a better understanding of the molecular mechanism of antibacterial defense and the containment of infectious bacterial diseases in grouper.

Background: Microsporidia are a group of obligated intracellular fungus pathogens. Monocytes and the derivative macrophages are among the most important players in host immunity. The invasion of microsporidia may significantly affect the monocytes maturation and extravasation processes. Methods: We utilized a previously established microsporidia infection murine model to investigate the influences of microsporidia Encephalitozoon hellem (E. hellem) infection on monocyte maturation, releasing into the circulation and extravasation to the inflammation site. Flow cytometry and qPCR analysis were used to compare the monocytes and derivative macrophages isolated from bone marrow, peripheral blood and tissues of E. hellem-infected and control mice. Results: The results showed that the pro-inflammatory group of CD11b+Ly-6C+ monocytes are promoted in E. hellem-infected mice. Interestingly, the percentage of Ly-6C+ monocytes from E. hellem-infected mice are significantly lower in peripheral blood while significantly higher in the inflamed small intestine, together with up-regulated ratio of F4/80 macrophage in small intestine as well. Conclusions: Our findings demonstrated that E. hellem infection leads to promoted monocytes maturation in bone marrow, up-regulation of extravasation from peripheral blood to inflammation site and maturation into macrophages. Our study is the first systematic analysis of monocytes maturation and trafficking during microsporidia infection, and will provide better understanding of the pathogen–host interactions.

The microphthalmia-associated transcription factor (MITF) is an important transcription factor that plays a key role in melanogenesis, cell proliferation, survival and immune defense in vertebrate. However, its function and function mechanism in bivalve are still rarely known. In this research, first, a Mitf gene was characterized from Pteria penguin (P. penguin). The PpMitf contained an open reading frame of 1,350 bp, encoding a peptide of 449 deduced amino acids with a highly conserved basic helix-loop-helix-leucine zipper (bHLH-LZ) domain. The PpMITF shared 55.7% identity with amino acid sequence of Crassostrea gigas (C. gigas). Tissue distribution analysis revealed that PpMitf was highly expressed in mantle and hemocytes, which were important tissues for color formation and innate immunity. Second, the functions of PpMitf in melanin synthesis and innate immunity were identified. The PpMitf silencing significantly decreased the tyrosinase activity and melanin content, indicating PpMitf involved in melanin synthesis of P. penguin. Meanwhile, the PpMitf silencing clearly down-regulated the expression of PpBcl2 (B cell lymphoma/leukemia-2 gene) and antibacterial activity of hemolymph supernatant, indicating that PpMitf involved in innate immunity of P. penguin. Third, the function mechanism of PpMitf in immunity was analyzed. The promoter sequence analysis of tyrosinase (Tyr) revealed two highly conserved E-box elements, which were specifically recognized by HLH-LZ of MITF. The luciferase activities analysis showed that Mitf could activate the E-box in Tyr promoter through highly conserved bHLH-LZ domain, and demonstrated that PpMitf involved in melanin synthesis and innate immunity by regulating tyrosinase expression. Finally, melanin from P. penguin, the final production of Mitf-Tyr-melanin pathway, was confirmed to have direct antibacterial activity. The results collectively demonstrated that PpMitf played a key role in innate immunity through activating tyrosinase-mediated melanin synthesis in P. penguin.

High-mobility group box1 (HMGB1) is a non-histone chromosome protein that not only participates in nuclear formation and transcriptional regulation of, but also acts as a pro-inflammatory factor. In this study, a HMGB1 gene (OnHMGB1) was identified and characterized from Nile tilapia (Oreochromis niloticus). The open reading frame of OnHMGB1 sequence was 621 bp, encoding a 207 amino acids peptide. The deduced OnHMGB1 protein contained two HMG boxes and an acidic tail, which shared high identities to other reported HMGB1. OnHMGB1 was widely distributed in many tissues of healthy tilapia and was significantly up-regulated in spleen and head kidney after Streptococcus agalactiae poly I:C stimulation in vivo. Moreover, the recombinant protein of OnHMGB1 (rOnHMGB1) could bind to DNA in a dose-dependent manner, promote inflammatory factor expression and bactericidal activity of monocytes/macrophages in vitro as well. Taken together, these results indicate that OnHMGB1 plays roles in immune response of Nile tilapia against pathogen infection.

Selenium nanoparticles (SeNPs) are a novel elemental form selenium and often reported to possess beneficial bioactivities such as anticancer, promoting bone growth and immunomodulation. Our previous study demonstrated that chitosan-stabilized SeNPs have strong activity in immunomodulation. However, the mechanism underlying the immunomodulation of SeNPs is still unknown. The aim of this study is to identify the molecular mechanisms involved in SeNP-induced immunomodulation. Using zebrafish, as a common immunological animal model with a highly conserved molecular mechanism with other vertebrates, we conducted serum proteomic and tissue transcriptome analyses on individuals fed with SeNP in healthy or disease conditions. We also compared differences between SeNPs and an exogenous antioxidant Trolox in immune activity and redox regulation. Our results suggest that the immunomodulation activity was highly related to antioxidant activity and lipid metabolism. Interestingly, the biological functions enhanced by SeNP were almost identical in the healthy and disease conditions. However, while the SeNP was suppressing ROS in healthy individuals, it promoted ROS formation during disease condition. This might be related to the defense mechanism against pathogens. SOD and NFkβ appeared to be the key molecular switch changing effect of SeNPs when individuals undergo infection, indicating the close relationship between immune and redox regulation.

To detection of pathogens DNA is considered a promising strategy in sick fish. The current standard for enumeration of pathogens to obtain colony forming units by plate counts has several drawbacks: long time to results, high variability. While qPCR can target genetic identity, its limitations require enumeration to be calculated from a relative standard curve. There is a growing interest in techniques that allows an absolute quantification of pathogens DNA which could be useful for early diagnosis. Recently, digital PCR mainly based on droplets generation, emerged as an affordable technology for precise and absolute quantification of nucleic acids. In this work, we described a new interesting approach for profiling Streptococcus agalactiae DNA in tilapia different tissues samples using a chip-based platform, the Quant Studio 3D digital PCR. A total of 120 tissue samples were analyzed by plant count, qPCR and chip-based dPCR. The cdPCR method had a 5% relative standard deviation (RSD), marking it more precise than plate counts and qPCR with an RSD of 15 % and 10 %. Given its reproducibility and reliability, our approach could be potentially applied for the identification and quantification of pathogens DNA in infected fish. As chip-digital PCR becomes more established, it would be a robust tool for quantitative assessment of S. agalactiae DNA copy number for diagnosis of Streptococcosis.

Aquaculture effluent is often associated with increased organic carbon, suspended solids, phosphates, nitrogenous species (nitrates, nitrites, and ammonia), chemical oxygen demand and biological oxygen demand. This is regarded as a global threat to aquatic ecosystems due to its influence on surrounding waters as well as groundwater. The threat of aquaculture effluent is not confined to the aquatic ecosystems as high levels of phosphorus and nitrogen may become poisonous to plants and change their protein synthesis, enzyme activities, photosynthesis, oxidative stress response, membrane permeability, and respiratory processes. Other forms of water pollution such as the presence of heavy metals as well as pathogenic microbes are issues of concern since they can be transferred through the food chain. Bacillus species have demonstrated great ability in the maintenance of water quality in aquaculture which is simple and cost-effective. This review highlights that Bacillus modulates a wide range of water quality parameters including physical (transparency and total dissolved solids) and chemical (pH, conductivity, chemical oxygen demand, dissolved oxygen, biological oxygen demand, alkalinity, phosphates, nitrogenous species, hardness) water quality parameters, heavy metals, oil spillage as well as maintenance of microbial balance; hence reduction in pathogenic microbes. The efficiency of Bacillus in modulating water quality is greatly dependent on factors such as mode of application, dissolved oxygen, pH, temperature, source of nutrients, strain type, and metal ions. This review further highlights aquaculture activities that lead to pollution and the possible mechanisms used by Bacillus for improving water quality. It is recommended that a range of optimum conditions be established to increase the efficiency of Bacillus in modulating water quality. A better understanding of Bacillus to the genetic level and the development of new genetic tools is also recommended since the ability of microorganisms to modulate water quality is related to their genetic make-up.

Galectin-8 is a member of the galectin family that is involved in immune response against pathogens. However, the roles of fish galectin-8 during pathogen infection require comprehensive studies. In this study, a galectin-8 homolog (OnGal8-like, OnGal8-L) was characterized from Nile tilapia (Oreochromis niloticus), and its roles in response to bacterial infection were analyzed. The OnGal8-L contains an open reading frame of 891 bp, encoding a peptide of 296 amino acids with two CRD regions of tandem-repeat galectin and two carbohydrate recognition sites. The OnGal8-L protein shares 46.42% identities with reported Oreochromis niloticus galectin-8 protein. Transcriptional expression analysis revealed that OnGal8-L was constitutively expressed in all examined tissues and was highly expressed in spleen. The transcript levels of OnGal8-L were up-regulated in the spleen, head kidney, and brain, following Streptococcus agalactiae (S. agalactiae) challenge. Further in vitro analysis indicated that the recombinant protein of OnGal8-L (rOnGal8L) could agglutinate erythrocyte, S. agalactiae, and A. hydrophila and bind S. agalactiae, A. hydrophila, and various PAMPs (lipopolysaccharides, lipoteichoic acid, poly I:C, peptidoglycan, galactose, mannose, and maltose). Also, rOnGal8L could regulate inflammatory-related gene expression, phagocytosis, and a respiratory burst of monocytes/macrophages. Moreover, in vivo analysis showed that OnGal8-L overexpression could protect O. niloticus from S. agalactiae infection through modulating serum antibacterial activity (AKP, ACP, and LZM), antioxidant capacity (CAT, POD, and SOD), and monocyte/macrophage proliferation and cytokine expression, as well as reducing bacterial burden and decreasing tissue damage. Our results collectively indicate that OnGal8-L plays important regulatory roles in immune response against bacterial infection.

Background Mammalian commensal microbiota play important roles in the health of its host. In comparison to terrestrial mammals, commensal microbiota of marine mammals is mainly focused on the composition and function of skin and gut microbiota, with less attention paid to the health impact of bacteria and viruses. Previous studies on sperm whales (Physeter catodon) have affirmed their important phylogenetic position; however, studies on their commensal microbiota have not been published, due to difficulty in sample collection. Methods Here, we sequenced the metagenomes of blood, muscle and fecal samples from a stranded sperm whale using the BGISEQ-500 platform. We compared the diversity and abundance of microbiomes from three different tissues and tried to search pathogenic bacterial and virulence genes probably related to the health of the sperm whale. We also performed 16S rDNA sequencing of the fecal sample to compare to published gut metagenome data from other marine mammals. Results Our results demonstrated notable differences in species richness and abundance in the three samples. Extensive bacteria, including Enterococcus faecium, Fusobacterium nucleatum, Pseudomonas aeruginosa, Streptococcus anginosus, Streptococcus pneumoniae, and Streptococcus suis, and five toxigenic Clostridium species usually associated with infection, were found in the three samples. We also found the taxa composition of sperm whale gut microbiota was similar to that of other whales, suggesting co-evolution with its host. This study is the first report of the sperm whale gut microbiome, and provides a foundation for the pathogen detection and health assessment of the sperm whale.

Ciliates are fundamental components of microzooplankton, with important ecological roles. However, ciliate communities are particularly difficult to monitor using conventional morphological approaches. New molecular tools, such as DNA metabarcoding, can facilitate the study of these communities. This study used high-throughput sequencing to examine the diversity and seasonal dynamics of ciliate communities in four estuarine ecosystems in the South China Sea from June 2019 to March 2020. The amplification of the V4 region of 18S rDNA using ciliate-specific primers identified a total of 1645 amplicon sequence variants (ASVs), corresponding to 13 ciliate classes, 97 families, and 157 genera. The dominant species across all four sampling stations were spirotrichs (including choreotrichs, oligotrichs, and stichotrichs), oligohymenophorean scuticociliates, litostomateans Didinium, and prostomateans Cryptocaryon. Significant differences in ciliate diversity and community composition in the four stations were mainly due to differences in rare, rather than abundant, ASVs. Analysis of the ciliate communities and seasonal patterns in their composition revealed that variations in habitat and environmental conditions have a greater effect than seasonal changes on community composition.

Scuticociliatosis is an invasive external or systemic infection caused by ciliated protozoa, mainly those within the subclass Scuticociliatia (scuticociliates). Many scuticociliates are fish pathogens, including Miamiensis avidus, Philasterides dicentrarchi, Pseudocohnilembus persalinus, and Uronema marinum. Our previous study showed that hemolysis-related genes derived from bacteria through horizontal gene transfer (HGT) may contribute to virulence in P. persalinus. Hemorrhagic lesions are a common feature of scuticociliatosis, but it is not known whether other scuticociliates also have bacteria-derived hemolysis-related genes. In this study, we constructed a high-quality macronuclear genome of another typical pathogenic scuticociliate, U. marinum. A total of 105 HGT genes were identified in this species, of which 35 were homologs of hemolysis-related genes (including hemolysin-like genes) that had previously been identified in P. persalinus. Sequencing of an additional five species from four scuticociliate families showed that bacteria-derived hemolysis-related genes (especially hemolysin-like genes) are widely distributed in scuticociliates. Based on these findings, we suggest that hemolysin-like genes may have originated before the divergence of scuticociliates.

Abstract Background As an efficient and high-quality additive in agriculture and forestry production, silicon (Si) plays an important role in alleviating heavy metal stress and improving plant growth. However, the alleviating effect of aluminum (Al) toxicity by Si in Eucalyptus is still incomplete. Results Here, a study was conducted using two Al concentrations (0 and 4.5 mM) with four Si concentrations (0, 0.5, 1, and 1.5 mM) to investigate plant growth, tolerance and antioxidant defense system in four Eucalyptus species (Eucalyptus tereticornis, Eucalyptus urophylla, Eucalyptus grandis, and Eucalyptus urophylla × Eucalyptus grandis). The results showed that the stress induced by 4.5 mM Al increased oxidative damage, disturbed the balance of enzymatic and non-enzymatic antioxidant systems, and negatively affected plant growth and tolerance quality in the four Eucalyptus species. However, the addition of 0.5 mM and 1 mM Si alleviated the effects of Al toxicity on plant growth and improved plant growth quality by strengthening stress tolerance. Besides, adding Si significantly facilitated the synergistic action of enzymatic and non-enzymatic antioxidant defenses, increased the removal of reactive oxygen species, reduced lipid peroxidation, and oxidative stress, and promoted the phytoremediation rate of the four Eucalyptus species by 18.7 ~ 34.8% compared to that in the absence of Si. Conclusions Silicon can alleviate the effect of Al toxicity by enhancing the antioxidant capacity and improving plant growth and tolerance quality. Hence, the application of Si is an effective method for the phytoremediation of Eucalyptus plantations in southern China.