Whole-Genome-Based Survey for Polyphyletic Serovars of Salmonella enterica subsp. enterica Provides New Insights into Public Health Surveillance.

Serotyping has traditionally been considered the basis for surveillance of Salmonella, but it cannot distinguish distinct lineages sharing the same serovar that vary in host range, pathogenicity and epidemiology. However, polyphyletic serovars have not been extensively investigated. Public health microbiology is currently being transformed by whole-genome sequencing (WGS) data, which promote the lineage determination using a more powerful and accurate technique than serotyping. The focus in this study is to survey and analyze putative polyphyletic serovars. The multi-locus sequence typing (MLST) phylogenetic analysis identified four putative polyphyletic serovars, namely, Montevideo, Bareilly, Saintpaul, and Muenchen. Whole-genome-based phylogeny and population structure highlighted the polyphyletic nature of Bareilly and Saintpaul and the multi-lineage nature of Montevideo and Muenchen. The population of these serovars was defined by extensive genetic diversity, the open pan genome and the small core genome. Source niche metadata revealed putative existence of lineage-specific niche adaptation (host-preference and environmental-preference), exhibited by lineage-specific genomic contents associated with metabolism and transport. Meanwhile, differences in genetic profiles relating to virulence and antimicrobial resistance within each lineage may contribute to pathogenicity and epidemiology. The results also showed that recombination events occurring at the H1-antigen loci may be an important reason for polyphyly. The results presented here provide the genomic basis of simple, rapid, and accurate identification of phylogenetic lineages of these serovars, which could have important implications for public health.

Tumor Necrosis Factor Receptor-Associated Factor 6 (TRAF6) Mediates Ubiquitination-Dependent STAT3 Activation upon Salmonella enterica Serovar Typhimurium Infection.

Salmonella enterica serovar Typhimurium can inject effector proteins into host cells via type III secretion systems (T3SSs). These effector proteins modulate a variety of host transcriptional responses to facilitate bacterial growth and survival. Here we show that infection of host cells with S Typhimurium specifically induces the ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6). This TRAF6 ubiquitination is triggered by the Salmonella pathogenicity island 1 (SPI-1) T3SS effectors SopB and SopE2. We also demonstrate that TRAF6 is involved in the SopB/SopE2-induced phosphorylation of signal transducer and activator of transcription 3 (STAT3), a signaling event conducive to the intracellular growth of S Typhimurium. Specifically, TRAF6 mediates lysine-63 ubiquitination within the Src homology 2 (SH2) domain of STAT3, which is an essential step for STAT3 membrane recruitment and subsequent phosphorylation in response to S Typhimurium infection. TRAF6 ubiquitination participates in STAT3 phosphorylation rather than serving as only a hallmark of E3 ubiquitin ligase activation. Our results reveal a novel strategy in which S Typhimurium T3SS effectors broaden their functions through the activation of host proteins in a ubiquitination-dependent manner to manipulate host cells into becoming a Salmonella-friendly zone.

Identification of TRAF6 as a ubiquitin ligase engaged in the ubiquitination of SopB, a virulence effector protein secreted by Salmonella typhimurium.

The phosphoinositide phosphatase SopB is one of the effectors injected by Salmonella typhimurium (S.typhimurium) that diversifies its function through a ubiquitin-dependent differential localization. However, it is unclear which E3 ubiquitin ligase is responsible for ubiquitination of SopB. Based on the E1-E2-E3 trio of enzymes responsible for the ubiquitin activation and translocation to substrate proteins, we constructed an in vitro assay of SopB ubiquitination. Using this assay, we purified an E3 ubiquitin ligase, TRAF6, from the Henle-407 S100 extraction that may be responsible for the ubiquitination of SopB. To investigate the functional correlation of TRAF6, we showed that recombinant TRAF6 specifically ubiquitinates SopB in a dose-dependent manner in vitro. Upon infection, the ubiquitination of SopB was absolutely blocked by TRAF6 deletion, as shown in Traf6(-/-) mouse embryonic fibroblasts (MEFs) compared with Traf6(+/+) MEFs. However, the ectopic expression of TRAF6 in Traf6(-/-) MEFs rescued the two species of ubiquitin-conjugated SopB, which strengthens the role of TRAF6 in SopB ubiquitination. The analysis of E2 revealed that UbcH5c and not other E2 conjugating enzymes are required for TRAF6-mediated SopB ubiquitination both in vitro and in vivo. In summary, these results suggest the relevance of UbcH5c/TRAF6 in SopB during S.typhimurium infection and thereby imply that S.typhimurium has evolved a mechanism of utilizing the host's E3 ubiquitin ligase to modify and modulate the function of its effector protein in order to ensure pathogen and host cell survival.

[Effects of nitric oxide on root growth and its oxidative damage in wheat seedling under salt stress].

Effects of nitric oxide (NO), a substance newly found to have protective functions in plants, on root growth of wheat (Triticum aestivum L. Yangmai 158) seedlings under salt stress were studied. Sodium nitroprusside (SNP), an NO donor, markedly alleviated the inhibitory effect of salt on root elongation at salt concentrations around 150 mmol/L, but was ineffective when NaCl concentration was at 300 mmol/L or higher. It was most effective at 0.05-0.1 mmol/L, and had harmful effect at 0.30-5 mmol/L. Furthermore, when wheat seedling roots were treated with 150 mmol/L NaCl in combination with 0.05 mmol/L SNP and NO scavenger (hemoglobin, Hb), NO(-)(2)/NO(-)(3) and K(3)Fe(CN)(6) as controls, both of which were the two other major products besides NO when SNP dissolved in water, respectively, activities of superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) were enhanced to some extent. While, the generation of O(-.)(2) and the accumulation of MDA and H(2)O(2) were alleviated. DNA laddering was observed when wheat seedling roots exposed to 150 mmol/L NaCl for 6 d, also suggesting that salt stress might induce oxidative damage in root-tips. In combination with hemoglobin, NO(-)(2)/NO(-)(3) and K(3)Fe(CN)(6) as controls, the results showed that NO could block DNA ladders. Above results suggest that it is NO rather than any substances which is protecting root-tip cells of wheat seedlings from oxidative damage caused by salt stress.