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Thermostable strains isolated from intestine of catfish were screened for their antagonism activity against Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC) and red head disease. Four thermostable strains were selected, and their antagonistic activity against E. ictaluri was compared. Adhesion to zebrafish larvae was determined as CFU/larva after exposure for 30min. The isolate Yab4 was found to be highly adhesive and was identified as Bacillus altitudinis based on a phylogenetic tree constructed using 16S rDNA and gyrB sequences. After 28d of feed supplementation with B. altitudinis Yab4, the growth performance of the treatment group is better than that of the control group, with a statistically significant difference observed between the two groups. Moreover, the innate immune indexes including alkaline phosphatase, lysozyme, and total proteins in serum increased significantly, and the expression levels of immune genes including IL-1β, TNF-α, and NF-κB p65 elevated significantly as well. Most importantly, the survival rate of the yellow catfish fed with B. altitudinis Yab4 supplementation reached 60%, marking a 35% increase compared to the control group when challenged with E. ictaluri HSN-1 infected intraperitoneally. This demonstrates that the potential of B. altitudinis Yab4 as a novel Bacillus probiotic to defend against E. ictaluri in catfish aquaculture through feed supplementation. [ABSTRACT FROM AUTHOR]

Vibrio harveyi is one of the most serious bacterial pathogens to aquatic animals worldwide. Evidence is mounting that coinfections caused by multiple pathogens are common in nature and can alter the severity of diseases in marine animals. However, bacterial coinfections involving V. harveyi have received little attention in mariculture. In this study, the results of pathogen isolation indicated that bacterial coinfection was a common and overlooked risk for hybrid groupers (♀ Epinephelus polyphekadion × ♂ E. fuscoguttatus) reared in an industrialized flow-through pattern in Hainan Province. The artificial infection in hybrid groupers revealed that coinfections with V. harveyi strain GDH11385 (a serious lethal causative agent to groupers) and other isolated pathogens resulted in higher mortality (46.67%) than infection with strain GDH11385 alone (33.33%), whereas no mortality was observed in single infection with other pathogens. Furthermore, the intestine, liver and spleen of hybrid groupers are target organs for bacterial coinfections involving V. harveyi. Based on the infection patterns found in this study, we propose that V. harveyi may have a specific spatiotemporal expression pattern of virulence genes when infecting the host. Taken together, bacterial coinfection with V. harveyi is a neglected high-risk lethal causative agent to hybrid groupers in the industrialized flow-through aquaculture systems in Hainan Province. [ABSTRACT FROM AUTHOR]

A 28‐day feeding trial was conducted to evaluate the effects of different dietary preparations of Enterococcus faecalis F7 (blank control (BC), dead bacteria (DB), live bacteria (EF), cell‐free extract of E. faecalis F7 (BF) and E. faecalis F7 treated with lithium chloride (Li)) on growth and intestinal microbiota of Litopenaeus vannamei. Results indicated that incorporation of live E. faecalis F7 into diet significantly improved the growth of L. vannamei by increasing weight gain rate (WGR), specific growth rate (SGR) and reducing feed conversion ratio (FCR). High‐throughput sequencing data showed that incorporation of various preparations of E. faecalis F7 into diet altered intestinal microbiota richness and diversity in L. vannamei. In particular, live E. faecalis F7 improved the health of shrimp by increasing the abundance of beneficial bacteria and reducing the abundance of detrimental bacteria in the gut tract. Moreover, stability of intestinal microbiota was maintained for more than 7 days when shrimps were fed on basic diet after administration of live E. faecalis F7 for 28 days. These results demonstrate that diet enriched with live E. faecalis F7 promotes the growth and modulates the intestinal microbiota in Pacific white shrimp (L. vannamei). [ABSTRACT FROM AUTHOR]

The stringent response mediated by the signal molecule (p)ppGpp is involved in response to multiple environmental stresses and control of various physiological processes. Studies have revealed that (p)ppGpp strongly affects the formation and maintenance of several bacterial biofilms. However, the specific regulatory roles of (p)ppGpp in biofilms, especially in the expression of genes related to cell motility and exopolysaccharides (EPSs) production, remain poorly understood. We recently reported two (p)ppGpp synthetase genes relA and spoT from the epizootic pathogen Vibrio alginolyticus. Herein, we found that the (p)ppGpp synthetase genes of V. alginolyticus contributed to biofilm formation at low cell density and biofilm detachment at high cell density, respectively, in polystyrene microtiter plates. Quantitative reverse transcription PCR (qRT-PCR) analysis revealed that the expression levels of both EPSs and motility associated genes were consistent with the development of biofilms. Besides, the (p)ppGpp synthetase gene spoT was found to be closely involved in the regulation of flagellum, smooth/translucent colony morphology and spotty pellicle at the air-liquid interface. Interestingly, pleiotropic phenotypes of Δ relA Δ spoT were similar to that of the rpoN (σ54) deletion mutant. Meanwhile, the absence of (p)ppGpp synthetase genes significantly reduced the expression levels of rpoN at low cell density, suggesting that (p)ppGpp may mediate the formation via positively affecting the alternative sigma factor RpoN. These findings allow us to propose (p)ppGpp as a crucial regulator for biofilm development in V. alginolyticus , in view of the regulatory roles of relA and spoT in cell motility and EPSs production. [ABSTRACT FROM AUTHOR]