Chryseobacterium montanum sp. nov. isolated from mountain soil.

A Gram-staining-negative, strictly aerobic, non-spore-forming, rod-shaped bacterium, designated WG4T, was isolated from soil of the Tianmen Mountain located in Hunan province, PR China. 16S rRNA gene sequence analysis showed that the strain belongs to the genus Chryseobacterium in the family Flavobacteriaceae, with 97.4 % and 97.1 % sequence identities to Chryseobacterium anthropi NF 1366T and Chryseobacterium haifense H38T, respectively. In comparison with the other strains representing the genus Chryseobacterium, the 16S rRNA gene sequence identities were less than 97.0 %. The DNA-DNA relatedness values were 63.3 % (±1) between C. anthropi NF 1366T and strain WG4T and 62.7 % (±2) between C. haifense DSM 19056T and strain WG4T. The DNA G+C content of strain WG4T was 37.7 mol%. The predominant fatty acids of strain WG4T were iso-C15 : 0, anteiso-C15 : 0 and iso-C17 : 0 3-OH. The major polar lipids were phosphatidylethanolamine, three unidentified lipids and two unidentified aminolipids. The major menaquinone of strain WG4T was menaquinone 6. Strain WG4T showed some unique physiological and biochemical characteristics, such as being negative for gelatin hydrolysis, and valine arylamidase and α-glucosidase activity, and positive for acid production from cellobiose. Based on the differentiating phylogenetic inference and biochemical data, strain WG4T represents a novel species, for which the name Chryseobacterium montanum sp. nov. is proposed, with the type strain WG4T (=KCTC 52204T=CCTCC AB 2016058T).

Novel bacterial selenite reductase CsrF responsible for Se(IV) and Cr(VI) reduction that produces nanoparticles in Alishewanella sp. WH16-1.

Alishewanella sp. WH16-1 is a facultative anaerobic bacterium isolated from mining soil. Under aerobic conditions, this bacterium efficiently reduces selenite and chromate. A flavoprotein showing 37% amino acid identity to E. coli chromate reductase ChrR was identified from the genome (named CsrF). Gene mutation and complementation along with heterologous expression revealed the ability of CsrF to reduce selenite and chromate in vivo. The purified CsrF was yellow and showed an absorption spectra similar to that of FMN. The molecular weight of CsrF was 23,906 for the monomer and 47,960 for the dimer. In vitro, CsrF catalyzes the reduction of Se(IV) and Cr(VI) using NAD(P)H as cofactors with optimal condition of pH 7.0 and temperature of 30-37°C. This enzyme also catalyze the reduction of sulfate and ferric iron but not arsenate and nitrate. Using NADPH as its electron donor, the Km for the reduction of Se(IV) and Cr(VI) was 204.1±27.91 and 250.6±23.46µmol/L, respectively. Site-directed mutagenesis showed that Arg13 and Gly113 were essential for the reduction of Se(IV) and Cr(VI). The products of the reduction of Se(IV) and Cr(VI) were Se(0)- and Cr(III)-nanoparticles, respectively. To our knowledge, CsrF is a novel and well-characterized bacterial aerobic selenite reductase.