天知 誠吾

Microbes have been shown to adapt to stressful or even lethal conditions through displaying genome plasticity. However, how bacteria utilize the ability of genomic plasticity to deal with high antimony (Sb) stress has remained unclear. In this study, the spontaneous mutant strain SMAs-55 of Achromobacter sp. As-55 was obtained under antimonite (Sb(III)) stress. SMAs-55 displayed significantly increased Sb(III) resistance, but it lost the ability to oxidize arsenite (As(III)) by deleting an entire gene island containing genes encoding functions involved in As(III) oxidation, arsenic (As)/Sb resistance and phosphate transport. This study suggests that genetic plasticity has played an important role in As-55 adaption to Sb(III) stress. Transcriptomic analysis found that genes encoding functions involved in capsule polysaccharide synthesis, as well as functions correlated to stress adaptation, ATP production, and metabolism were more strongly expressed in SMAs-55. In addition, a lower intracellular Sb(III) accumulation in SMAs-55 was observed. These findings indicate that reduced uptake through increased capsule biosynthesis was an effective way for SMAs-55 to adapt to an environment displaying high levels of Sb. This study helps us to better understand the evolutionary processes enabling survival of microbes and microbial community in contaminated environments.

Intrasporangium sp. strain DVR is an actinobacterium of the family Intrasporangiaceae isolated from soil in Japan. Here we report the draft genome sequence of strain DVR.

Geobacter sp. strain SVR uses antimonate [Sb(V)] as a terminal electron acceptor for anaerobic respiration. Here, we visualized a possible key enzyme, periplasmic Sb(V) reductase (Anr), via active staining and non-denaturing gel electrophoresis. Liquid chromatography-tandem mass spectrometry analysis revealed that a novel dimethyl sulfoxide (DMSO) reductase family protein, WP_173201954.1, is involved in Anr. This protein was closely related with AnrA, a protein suggested to be the catalytic subunit of a respiratory Sb(V) reductase in Desulfuribacillus stibiiarsenatis. The anr genes of strain SVR (anrXSRBAD) formed an operon-like structure, and their transcription was upregulated under Sb(V)-respiring conditions. The expression of anrA gene was induced by more than 1 µM of antimonite [Sb(III)]; however, arsenite [As(III)] did not induce the expression of anrA gene. Tandem mass tag-based proteomic analysis revealed that, in addition to Anr proteins, proteins in the following categories were upregulated under Sb(V)-respiring conditions: (i) Sb(III) efflux systems such as Ant and Ars; (ii) antioxidizing proteins such as ferritin, rubredoxin, and thioredoxin; (iii) protein quality control systems such as HspA, HslO, and DnaK; and (iv) DNA repair proteins such as UspA and UvrB. These results suggest that strain SVR copes with antimony stress by modulating pleiotropic processes to resist and actively metabolize antimony. To the best of our knowledge, this is the first report to demonstrate the involvement of AnrA in Sb(V) respiration at the protein level. Furthermore, this is the first example to show high expression of the Ant system proteins in the Sb(V)-respiring bacterium.IMPORTANCEAntimony (Sb) exists mainly as antimonite [Sb(III)] or antimonate [Sb(V)] in the environment, and Sb(III) is more toxic than Sb(V). Recently, microbial involvement in Sb redox reactions has received attention. Although more than 90 Sb(III)-oxidizing bacteria have been reported, information on Sb(V)-reducing bacteria is limited. Especially, the enzyme involved in dissimilatory Sb(V) reduction, or Sb(V) respiration, is unclear, despite this pathway being very important for the circulation of Sb in nature. In this study, we demonstrated that the Sb(V) reductase (Anr) of an Sb(V)-respiring bacterium (Geobacter sp. SVR) is a novel member of the dimethyl sulfoxide (DMSO) reductase family. In addition, we found that strain SVR copes with Sb stress by modulating pleiotropic processes, including the Ant and Ars systems, and upregulating the antioxidant and quality control protein levels. Considering the abundance and diversity of putative anr genes in the environment, Anr may play a significant role in global Sb cycling in both marine and terrestrial environments.

Iodate reductase (Idr) gene cluster (idrABP1P2 ) is involved in bacterial iodate (IO3 -) respiration under anaerobic conditions. Putative idr gene clusters are present in both anaerobic and aerobic bacteria; however, the specific physiological roles of idr genes in aerobic bacteria remain unclear. Therefore, in this study, three marine aerobic bacteria with putative idr gene clusters (Roseovarius azorensis, Notoacmeibacter marinus, and Aliiroseovarius sediminilitoris) were grown in the presence of iodate to determine whether they can reduce iodate to iodide (I-). All tested bacteria almost completely reduced 2 mM iodate under static conditions but only reduced 0.1-0.5 mM iodate under shaking conditions. Moreover, the washed cell suspension of R. azorensis reduced iodate only when the cells were pre-grown statically in the presence of iodate. Transcriptional analysis revealed that the expression levels of idrA, idrB, idrP1 , and idrP2 genes were upregulated in R. azorensis when the cells were grown statically in the presence of iodate. Specifically, idrA expression was induced by 0.1 μM iodate and was up to 14-fold higher compared to that of the non-iodate control. These results suggest that marine aerobic bacteria reduce iodate under oxygen-limited conditions, and that this capacity is induced by environmentally relevant levels of iodate in seawater. Our results suggest that marine aerobic bacteria contribute to iodide production in marine surface waters, thereby affecting the global iodine cycling and ozone budget.

Pelosinus sp. strain IPA-1 is a bacterium isolated from arsenic-contaminated soil in Japan. We here report the draft genome sequence of strain IPA-1.