Search

Two Gram-stain-negative, facultative anaerobic, rod-shaped bacterial strains, S171 T and S2-9, were isolated from seleniferous soil in China. Comprehensive phylogenetic analyses based on 16S rRNA genes, multilocus sequences and whole genome sequences indicated that the two strains belonged to the genus Citrobacter . The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of strains S171 T and S2-9 with the closest relative Citrobacter koseri NCTC 10786 T were 83.6-83.7% and 27.7-27.8 %, respectively, which were below the species cutoff values. The ANI and dDDH values between the two strains were 97.9% and 84.8 %, respectively. The biochemical characteristics revealed that selenite tolerance, H 2 S and indole production, arginine dihydrolase, ornithine decarboxylase, as well as acid production from carbon sources such as d-sorbitol and arbutin are distinctive features of the two strains. Based on these results, strain S171 T and strain S2-9 represent a novel species of the genus Citrobacter , for which the name Citrobacter enshiensis sp. nov. is proposed, with strain S171 T (=GDMCC 1.3637 T =JCM 35851 T ) as the type strain. The genome size of strain S171 T was 4.92 Mb with a G+C content of 52.6 mol%. The genome size of strain S2-9 was 4.89 Mb with a G+C content of 52.6 mol%.

Microbial transformation of selenite [Se(IV)] to elemental selenium nanoparticles (SeNPs) is known to be an important process for removing toxic soluble selenium (Se) oxyanions and recovery of Se from the environment as valuable nanoparticles. However, the mechanism of selenite uptake by microorganisms, the first step through which Se exerts its cellular function, remains not well studied. In this study, the effects of selenite concentration, time, pH, metabolic inhibitors, and anionic analogues on selenite uptake in Rahnella aquatilis HX2 were investigated. Selenite uptake by R . aquatilis HX2 was concentration- and time-dependent, and its transport activity was significantly dependent on pH. In addition, selenite uptake in R . aquatilis HX2 was significantly inhibited by the aquaporin inhibitor AgNO 3 and sulfite (SO 3 2- ), and partially inhibited by carbonyl cyanide m -chlorophenyl hydrazone (CCCP) and 2,4-dinitrophenol (2,4-DNP) treatments. Three mutants with in-frame deletions of aqp Z, glp F, and nha A genes were constructed. The transport assay showed that the water channel protein AqpZ, and not GlpF, was a key channel of selenite uptake by R . aquatilis HX2, and sulfite and selenite had a common uptake pathway. In addition, the Na + /H + antiporter NhaA is also involved in selenite uptake in R . aquatilis HX2.