Disrupting ROS-protection mechanism allows hydrogen peroxide to accumulate and oxidize Sb(III) to Sb(V) in Pseudomonas stutzeri TS44.

BACKGROUND: Microbial antimonite [Sb(III)] oxidation converts toxic Sb(III) into less toxic antimonate [Sb(V)] and plays an important role in the biogeochemical Sb cycle. Currently, little is known about the mechanisms underlying bacterial Sb(III) resistance and oxidation. RESULTS: In this study, Tn5 transposon mutagenesis was conducted in the Sb(III)-oxidizing strain Pseudomonas stutzeri TS44 to isolate the genes responsible for Sb(III) resistance and oxidation. An insertion mutation into gshA, encoding a glutamate cysteine ligase involved in glutathione biosynthesis, generated a strain called P. stutzeri TS44-gshA540. This mutant strain was complemented with a plasmid carrying gshA to generate strain P. stutzeri TS44-gshA-C. The transcription of gshA, the two superoxide dismutase (SOD)-encoding genes sodB and sodC as well as the catalase-encoding gene katE was monitored because gshA-encoded glutamate cysteine ligase is responsible for the biosynthesis of glutathione (GSH) and involved in the cellular stress defense system as are superoxide dismutase and catalase responsible for the conversion of ROS. In addition, the cellular content of total ROS and in particular H2O2 was analyzed. Compared to the wild type P. stutzeri TS44 and TS44-gshA-C, the mutant P. stutzeri TS44-gshA540 had a lower GSH content and exhibited an increased content of total ROS and H2O2 and increased the Sb(III) oxidation rate. Furthermore, the transcription of sodB, sodC and katE was induced by Sb(III). A positive linear correlation was found between the Sb(III) oxidation rate and the H2O2 content (R 2 = 0.97), indicating that the accumulated H2O2 is correlated to the increased Sb(III) oxidation rate. CONCLUSIONS: Based on the results, we propose that a disruption of the pathway involved in ROS-protection allowed H2O2 to accumulate. In addition to the previously reported enzyme mediated Sb(III) oxidation, the mechanism of bacterial oxidation of Sb(III) to Sb(V) includes a non-enzymatic mediated step using H2O2 as the oxidant.

Draft genomic sequence of a selenite-reducing bacterium, Paenirhodobacter enshiensis DW2-9(T).

Paenirhodobacter enshiensis is a non-photosynthetic species that belongs to family Rhodobacteraceae. Here we report the draft genome sequence of Paenirhodobacter enshiensis DW2-9(T) and comparison results to the available related genomes. The strain has a 3.4 Mbp genome sequence with G + C content of 66.82 % and 2781 protein-coding genes. It lacks photosynthetic gene clusters and putative proteins necessary in Embden-Meyerhof-Parnas (EMP) pathway, but contains proteins in Entner-Doudoroff (ED) pathway instead. It shares 699 common genes with nine related Rhodobacteraceae genomes, and possesses 315 specific genes.

Flavobacterium hauense sp. nov., isolated from soil and emended descriptions of Flavobacterium subsaxonicum, Flavobacterium beibuense and Flavobacterium rivuli.

A strictly aerobic, Gram-staining-negative, rod-shaped, non-motile, yellow-pigmented bacterial strain, designated BX12(T), was isolated from soil collected from the peak area of Wudang Mountain in the city of Shiyan, Hubei province, China. Phylogenetic analysis of the 16S rRNA gene sequences showed that strain BX12(T) was most closely related to Flavobacterium subsaxonicum WB 4.1-42(T) (95.9% 16S rRNA gene sequence similarity), followed by Flavobacterium beibuense F44-8(T) (95.6%) and Flavobacterium rivuli WB 3.3-2(T) (94.1%). The major fatty acids (≥5%) of strain BX12(T) were summed feature 3 (comprising C(16:1)ω7c and/or C(16:1)ω6c), iso-C(15:0), C(16:0), iso-C(17:0) 3-OH, and C(16:0) 3-OH. The major polar lipid was phosphatidylethanolamine, and the major respiratory quinone was menaquinone-6. The genomic DNA G+C content was 43.9 mol%. On the basis of a high number of phenotypic differentiating properties and phylogenetic uniqueness, strain BX12(T) represents a novel species of the genus Flavobacterium for which the name Flavobacterium hauense sp. nov. is proposed. The type strain is BX12(T) ( =CCTCC AB 2012197(T) =KCTC 32147(T)). Emended descriptions of Flavobacterium subsaxonicum, Flavobacterium beibuense and Flavobacterium rivuli are also proposed.