RpoS and oxidative stress conditions regulate succinyl‐CoA: 3‐ketoacid‐coenzyme A transferase (SCOT) expression in Burkholderia pseudomallei

Burkholderia pseudomallei, a pathogenic gram‐negative bacterium, causes the severe human disease melioidosis. This organism can survive in eukaryotic host cells by escaping reactive oxygen species via the regulation of stress responsive sigma factors, including RpoS. In B. pseudomallei, RpoS has been reported to play a role in the oxidative stress response through enhanced activity of OxyR and catalase. In this study, the RpoS dependent oxidative stress responsive system was further characterized using comparative proteomic analysis. The proteomic profiles of wild‐type B. pseudomallei following exposure to H₂O₂ and between wild‐type and the rpoS mutant strains were analyzed. Using stringent criteria, 13 oxidative responsive proteins, eight of which are regulated by RpoS, were identified with high confidence. It was observed that ScoA, a subunit of the SCOT enzyme not previously shown to be involved directly in the oxidative stress response, is significantly down‐regulated after hydrogen peroxide treatment. ScoA and ScoB have been predicted to be organized in a single operon using computational methods: in this study it was confirmed by RT‐PCR that these genes are indeed co‐transcribed as a single mRNA. The present study is the first to report a role for RpoS in the down‐regulation of SCOT expression in response to oxidative stress in B. pseudomallei.     

hSSB1 rapidly binds at the sites of DNA double-strand breaks and is required for the efficient recruitment of the MRN complex

hSSB1 is a newly discovered single-stranded DNA (ssDNA)-binding protein that is essential for efficient DNA double-strand break signalling through ATM. However, the mechanism by which hSSB1 functions to allow efficient signalling is unknown. Here, we show that hSSB1 is recruited rapidly to sites of double-strand DNA breaks (DSBs) in all interphase cells (G1, S and G2) independently of, CtIP, MDC1 and the MRN complex (Rad50, Mre11, NBS1). However expansion of hSSB1 from the DSB site requires the function of MRN. Strikingly, silencing of hSSB1 prevents foci formation as well as recruitment of MRN to sites of DSBs and leads to a subsequent defect in resection of DSBs as evident by defective RPA and ssDNA generation. Our data suggests that hSSB1 functions upstream of MRN to promote its recruitment at DSBs and is required for efficient resection of DSBs. These findings, together with previous work establish essential roles of hSSB1 in controlling ATM activation and activity, and subsequent DSB resection and homologous recombination (HR).     

<Emphasis Type="Italic">Actimicrobium antarcticum</Emphasis> gen. nov., sp. nov., of the Family <Emphasis Type="Italic">Oxalobacteraceae</Emphasis>, Isolated from Antarctic Coastal Seawater

A Gram-negative, non-motile, catalase- and oxidase- positive, strictly aerobic, and short rod-shaped bacterium that was designated strain KOPRI 25157^T was isolated from coastal seawater sample in Antarctica. The temperature and pH ranges for growth on R2A agar were 10–20°C, and 5.0–10.0, respectively. Phylogenetic analyses of the 16S rRNA gene sequence of strain KOPRI 25157^T showed it to belong to the family Oxalobacteraceae of the class Betaproteobacteria, and it formed a distinct clade from other recognized members of the family. DNA G + C content was 65.9 mol%. Major ubiquinone was Q-8. Predominant cellular fatty acids were C_16:1 ω7c/15 iso 2OH (56.4%) and C_16:1 (30.5%). Major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, and unknown lipid. On the basis of these data, it is proposed that strain KOPRI 25157^T is the representative of a novel genus, for which the name Actimicrobium gen. nov. is proposed in the family Oxalobacteraceae. The type strain for Actimicrobium antarcticum sp. nov. is KOPRI 25157^T (=JCM 16673^T=KCTC 23040^T).     

Polar and Alpine Microbial Collection (PAMC): a culture collection dedicated to polar and alpine microorganisms

Microorganisms in polar areas may have important ecological roles in biogeochemical cycles and the food chain. They are adapted to polar environments by means of special physiological adaptation mechanisms that include cold-adapted enzymes and cryoprotectants such as exopolysaccharides. Culture collections for polar microorganisms can provide research resources for ecological and physiological studies. The Polar and Alpine Microbial Collection (PAMC) is a specialized culture collection for maintenance and distribution of polar and alpine microorganisms. A database system was developed to share important data fields with DarwinCore2 and Ocean Biogeographic Information System database schemas. Approximately 1,500 out of 5,500 strains maintained in PAMC have been identified and belonged primarily to the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Many of the microbial strains can grow at low temperature and produce proteases, lipases, and/or exopolysaccharides. PAMC provides search tools based on keywords such as taxonomy, geographical origin, habitat, and physiological characteristics. Biological materials and information provided by PAMC will be important resources for ecological and physiological studies on polar and alpine microorganisms.     

Ohioensins F and G: protein tyrosine phosphatase 1B inhibitory benzonaphthoxanthenones from the Antarctic moss Polytrichastrum alpinum

Ohioensins F and G (1 and 2), two new benzonaphthoxanthenones, have been isolated from the MeOH extract of Antarctic moss Polytrichastrum alpinum by various chromatographic methods. The structures of these compounds were determined mainly by analysis of NMR spectroscopic data. The known compounds ohioensins A and C (3 and 4) were also obtained. Compounds 1-4 showed potent inhibitory activity against therapeutically targeted protein tyrosine phosphatase 1B (PTP1B). Kinetic analysis of PTP1B inhibition by ohioensin F (1) suggested that benzonaphthoxanthenones inhibited PTP1B activity in a non-competitive manner.     

Regulation of helper T cell responses to staphylococcal superantigens

Staphylococcal superantigens (sAgs) including toxic shock syndrome toxin-1 (TSST-1) and related enterotoxins are exoproteins with unique immunobiological properties. They bind to major histocompatibility complex (MHC) class II molecules of antigen-presenting cells outside the peptide groove, and induce massive proliferation of T cells bearing specific V beta determinants. This tri-molecular interaction leads to uncontrolled release of various proinflammatory cytokines especially interferon-gamma (IFN-gamma) and tumor necrosis factor-a (TNF-alpha), the key cytokines causing sAg-mediated shock. The effector T cells involved in this hyper-immune response are predominantly of the T helper-1 (Th1) phenotype. There is also some evidence that polarization to a Th2 response with the production of classical anti-inflammatory cytokines (such as interleukins IL-4 and IL-6) also occurs. Moreover, the emergence of a novel regulatory T cell (Tr1) subset, producing mainly IL-10 but little or no IL-2 and IL-4, has recently been described following repeated sAg stimulation. In this review, the current knowledge regarding the regulation of T helper cell subsets in response to staphylococcal sAgs is critically evaluated, and the role of various cytokines which directly influence T cell differentiation and polarization is summarized. Particular emphasis is directed towards pro-inflammatory as well as anti-inflammatory and regulatory effector functions during toxic shock. Based on this review, we propose that a delayed production of IL-10 by Tr1 cells may be the most prominent driving force in the down-regulation of the Th1 hyper-immune response, and the critical determinant for the eventual recovery of the host.