Complete genome analysis of a virulent Vibrio scophthalmi strain VSc190401 isolated from diseased marine fish half-smooth tongue sole, Cynoglossus semilaevis.

BACKGROUND: Vibrio scophthalmi is an opportunistic bacterial pathogen, which is widely distributed in the marine environment. Earlier studies have suggested that it is a normal microorganism in the turbot gut. However, recent studies have confirmed that this bacterial strain can cause diseases in many different marine animals. Therefore, it is necessary to investigate its whole genome for better understanding its physiological and pathogenic mechanisms. RESULTS: In the present study, we obtained a pathogenic strain of V. scophthalmi from diseased half-smooth tongue sole (Cynoglossus semilaevis) and sequenced its whole genome. Its genome contained two circular chromosomes and two plasmids with a total size of 3,541,838 bp, which harbored 3185 coding genes. Among these genes, 2648, 2298, and 1915 genes could be found through annotation information in COG, Blast2GO, and KEGG databases, respectively. Moreover, 10 genomic islands were predicted to exist in the chromosome I through IslandViewer online system. Comparison analysis in VFDB and PHI databases showed that this strain had 334 potential virulence-related genes and 518 pathogen-host interaction-related genes. Although it contained genes related to four secretion systems of T1SS, T2SS, T4SS, and T6SS, there was only one complete T2SS secretion system. Based on CARD database blast results, 180 drug resistance genes belonging to 27 antibiotic resistance categories were found in the whole genome of such strain. However, there were many differences between the phenotype and genotype of drug resistance. CONCLUSIONS: Based on the whole genome analysis, the pathogenic V. scophthalmi strain contained many types of genes related to pathogenicity and drug resistance. Moreover, it showed inconsistency between phenotype and genotype on drug resistance. These results suggested that the physiological mechanism seemed to be complex.

First report of isolation and complete genome of Vibrio rotiferianus strain SSVR1601 from cage-cultured black rockfish (Sebastes schlegelii) associated with skin ulcer.

Vibrio rotiferianus is an important marine pathogen of various aquatic organisms and can be found widely distributed in the marine environment. To further characterize this pathogen, the pathogenic properties and genome of V. rotiferianus SSVR1601 isolated from Sebastes schlegelii with skin ulcer were analysed. SSVR1601 was shown to be short rod-shaped cell with a single polar flagellum. Different degrees of pathological changes in fish kidney, intestine, gills and liver were observed after SSVR1601 challenge. The SSVR1601 genome consists of two chromosomes and two plasmids with a total of 5,717,113 bp, 42.04%-44.93% GC content, 5,269 predicted CDSs, 134 tRNAs and 40 rRNAs. The common virulence factors including OMPs, haemolysin, flagellin, DNase, entF, algU, tcpI, acfB and rfaD were found in strain SSVR1601. Furthermore, factors responsible for iron uptake (fur, fepC and ccmC) and types II, IV and VI secretion systems were detected, which are likely responsible for the pathogenicity of SSVR1601. The antimicrobial resistance genes, bacA, tet34 and norM, were detected based on Antibiotic Resistance Genes Database. The phylogenetic analysis revealed SSVR1601 to be most closely related to V. rotiferianus strains CAIM577 and B64D1.

Development of a new protocol for freeze-drying preservation of Pseudoalteromonas nigrifaciens and its protective effect on other marine bacteria

Background: Freeze-drying is known as one of the best methods to preserve bacterial strains. Protectant is the key factor affecting the survival rate of freeze-dried strains. In addition, salinity, bacterial suspension concentration, drying time, and other factors can also affect the survival rate of strains to varying degrees. At present, there are relatively few studies on freeze-drying preservation of marine bacteria. In the present study, we performed the freeze-drying protectant screening and optimized the preservation conditions for Pseudoalteromonas nigrifaciens, which is widely distributed in marine environment. The protective effects of the screened protectants were verified by 18 other marine bacterial strains. Results: The results indicated that the combination of 5.0% (w/v) lactose, 5.0% (w/v) mannitol, 5.0% (w/v) trehalose, 10.0% (w/v) skim milk powder, 0.5% (w/v) ascorbic acid and 0.5% (w/v) gelatin was the best choice for the preservation of P. nigrifaciens. The suggested salinity and concentration of initial cell suspension were 10 g/L NaCl and 1.0 × 109 CFU/mL, respectively. Furthermore, stationary-phase cells were the best choice for the freeze-drying process. The highest survival rate of P. nigrifaciens reached 52.8% when using 5­10% (w/v) skim milk as rehydration medium. Moreover, the other 18 marine strains belonging to Pseudoalteromonas, Vibrio, Photobacterium, Planomicrobium, Edwardsiella, Enterococcus, Bacillus, and Saccharomyces were freezedried under the abovementioned conditions. Their survival rates were 2.3­95.1%. Conclusion: Collectively, our results supported that the protectant mixture and parameters were beneficial for lyophilization of marine bacteria