Chemolithoautotrophic arsenite oxidation by a thermophilic Anoxybacillus flavithermus TCC9-4 from hot spring in Tengchong of Yunnan, China

A new facultative chemolithoautotrophic arsenite-oxidizing bacterium TCC9-4 was isolated from a hot spring microbial mat in Tengchong of Yunnan, China. This strain could grow with arsenite (AsIII) as an energy source, CO2-HCO3- as a carbon source and oxygen as the electron acceptor in a minimal salts medium. Under chemolithoautotrophic conditions, more than 90 % of 100 mg/L AsIII could be oxidized by the strain TCC9-4 in 36 hours. Temperature was an important environmental factor that strongly influenced AsIII oxidation rate and AsIII oxidase (Aio) activity; highest Aio activity was found at the optimal temperature of 40 oC. Addition of 0.01 % yeast extract enhanced the growth significantly, but delayed the AsIII oxidation. On the basis of 16S rDNA phylogenetic sequence analysis, strain TCC9-4 was identified as Anoxybacillus flavithermus. To our best knowledge, this is the first report of arsenic oxidation by Anoxybacillus flavithermus. The results of this study expand our current understanding of microbially-mediated arsenic oxidation in hot spring

Polyamine regulates tolerance to water stress in leaves of white clover associated with antioxidant defense and dehydrin genes via involvement in calcium messenger system and hydrogen peroxide signaling

Endogenous polyamine (PA) may play a critical role in tolerance to water stress in plants acting as a signaling molecule activator. Water stress caused increases in endogenous PA content in leaves, including putrescine (Put), spermidine (Spd), and spermine (Spm). Exogenous application of Spd could induce the instantaneous H2O2 burst and accumulation of cytosolic free Ca2+, and activate NADPH oxidase and CDPK gene expression in cells. To a great extent, PA biosynthetic inhibitor reduced the water stress-induced H2O2 accumulation, free cytosolic Ca2+ release, antioxidant enzyme activities and genes expression leading to aggravate water stress-induced oxidative damage, while these suppressing effects were alleviated by the addition of exogenous Spd, indicating PA was involved in water stress-induced H2O2 and cytosolic free Ca2+ production as well as stress tolerance. Dehydrin genes (Y2SK, Y2K, and SK2) were showed to be highly responsive to exogenous Spd. PA-induced antioxidant defense and dehydrin genes expression could be blocked by the scavenger of H2O2 and the inhibitors of H2O2 generation or Ca2+ channels blockers, a calmodulin antagonist, as well as the inhibitor of CDPK. These findings suggested that PA regulated tolerance to water stress in white clover associated with antioxidant defenses and dehydrins via involvement in the calcium messenger system and H2O2 signaling pathways. PA-induced H2O2 production required Ca2+ release, while PA-induced Ca2+ release was also essential for H2O2 production, suggesting an interaction between PA-induced H2O2 and Ca2+ signaling

Characterization of carbapenem-resistant Acinetobacter baumannii isolates in a Chinese teaching hospital

Carbapenem-resistant Acinetobacter baumannii (CRAB) presents a serious therapeutic and infection control challenge. In this study, we investigated the epidemiological and molecular differences of CRAB, and the threatening factors for contributing to increased CRAB infections at a hospital in western China. 110 clinical isolates of A. baumannii, collected in last two years, were tested for carbapenem antibiotic susceptibility, followed by a molecular analysis of carbapenemase genes. Genetic relatedness of the isolates was characterised by multilocus sequence typing (MLST). 67 of the 110 isolates (60.9%) were resistant to carbapenem, 54 (80.60%, 54/67) of which carried the blaOXA-23 gene, most of them are classified as clone complex 92 (CC92). 77.62% of the 67 CRAB isolates were classified to CC92, and sequence type (ST) 92 was the most prevalent STs, followed by ST195, ST136, ST843 and ST75. One CRAB isolate of ST195 harbored plasmid pAB52 from a Chinese patient without travel history. The toxin-antitoxin elements of pAB52 related to adaptation for growth, which might have emerged as a common vehicle indirectly mediating the spread of OXA-23 in CRAB. Thus, CC92 A. baumannii carrying OXA-23 is a major drug resistant strain spreading in China. Our findings indicate that rational application of antibiotics is indispensable for avoiding widespread of drug resistance