Sphingobium paulinellae and Sphingobium algicola Lee and Jeon 2017 are two later heterotypic synonyms of Sphingobium limneticum Chen et al. 2013 and emended description of the species.

Phylogenetic analysis of the genus Sphingobium had shown that the type strains of Sphingobium paulinellae, Sphingobium algicola and Sphingobium limneticum shared a very close relationship between each other. The 16S rRNA gene sequences similarity values between each other ranged from 99.65 to 99.93 %. Whole genome sequencing was performed and genomic relatedness values between each pair of the species were 97.49-100 % (ANI) and 79.3-100 % (dDDH), respectively, all higher than the threshold values of 95-96 % ANI and 70 % dDDH suggested for species discrimination, and implicated that the type strains should belong to the same species of the genus Sphingobium. The phenotypic and chemotaxonomic characterizations performed in the original descriptions of S. paulinellae and S. algicola also supported the same conclusion. Due to priority of publication Sphingobium paulinellae and Sphingobium algicola Lee and Jeon 2017, should be taken as two later heterotypic synonyms of Sphingobium limneticum Chen et al. 2013. Correspondingly, the species description of Sphingobium limneticum was emended based on this study.

Characterization of role of the toxR gene in the physiology and pathogenicity of Vibrio alginolyticus.

toxR, a conserved virulence-associated gene in vibrios, is identified in Vibrio alginolyticus ZJ51-O, a pathogenic strain isolated from diseased fish. To reveal the role of ToxR in the pathogenicity of V. alginolyticus, a deletion mutant was constructed by allelic exchange. The mutant showed the same level of growth in trypticase soy broth (TSB) and iron-limiting condition, as the wild type strain. However, deletion of toxR severely reduced resistance against bile salts and the capability of biofilm formation. Outer-membrane protein (OMP) analysis showed that a 37-kD protein was absent and a 43-kD protein was decreased in the mutant. By MS/MS, the two proteins are identified as the homologues of OmpT and OmpN, respectively. These data suggest that ToxR might have enhanced the bile resistance and biofilm formation through modulating the production of OMP without affecting the ability of iron acquisition and the virulence to the fish via injection. These results indicate that ToxR may assist V. alginolyticus to colonize on the surface of the fish intestine which is crucial for the initiation of the infection, though it may not be involved in the proliferation of the bacteria in the host tissue.

The type III secretion system of Vibrio alginolyticus induces rapid apoptosis, cell rounding and osmotic lysis of fish cells.

Vibrio alginolyticus is a Gram-negative bacterium and has been recognized as an opportunistic pathogen in humans as well as marine animals. However, the virulence mechanisms for this species of Vibrio have not been elucidated. This study characterized multiple mechanisms that induce cell death in fish cells upon infection with a V. alginolyticus strain, ZJO. The bacterium required its type III secretion system (T3SS) to cause rapid death of infected fish cells. Dying cells exhibited some features of apoptotic cells, such as membrane blebbing, nuclear condensation and DNA fragmentation. Further studies showed that caspase-3 was activated by the T3SS of the ZJO strain, confirming that infection with V. alginolyticus rapidly induces T3SS-dependent apoptosis in fish cells. Infection with the ZJO strain also led to membrane pore formation and release of cellular contents from infected fish cells, as evidenced by lactate dehydrogenase release and the uptake of a membrane-impermeable dye. Importantly, inhibition of apoptosis did not prevent ZJO-infected cells from releasing cellular contents and did not block cell rounding. Taken together, these data demonstrate that infection with V. alginolyticus may promote at least three different T3SS-dependent events, which lead to the death of fish cells. This study provides an important insight into the mechanism used by Vibrio species to cause host-cell death.

Sensitive and rapid identification of Vibrio vulnificus by loop-mediated isothermal amplification.

Vibrio vulnificus is a serious bacterial pathogen for humans and aquatic animals. We developed a rapid, sensitive and specific identification method for V. vulnificus using loop-mediated isothermal amplification (LAMP) technique. A set of primers, composed of two outer primers and two inner primers, was designed based on the cytolysin gene sequence of V. vulnificus. The LAMP reaction was processed in a heat block at 65 degrees C for 60 min. The amplification products were detected by visual inspection using SYBR Green I, as well as by electrophoresis on agarose gels. Our results showed that the LAMP reaction was highly specific to V. vulnificus. This method was 10-fold more sensitive than conventional PCR. In conclusion, the LAMP assay was extremely rapid, simple, cost-effective, sensitive and specific for the rapid identification of V. vulnificus.