Graduate School of Horticulture, Chiba University, Matsudo, Chiba, Japan.
Center for Regional Environmental Research, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan.
Appl Environ Microbiol. 2024 Mar 20;90(3):e0172923. doi: 10.1128/aem.01729-23. Epub 2024 Feb 27.
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 . The genes of strain SVR () formed an operon-like structure, and their transcription was upregulated under Sb(V)-respiring conditions. The expression of gene was induced by more than 1 µM of antimonite [Sb(III)]; however, arsenite [As(III)] did not induce the expression of 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 ( 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 genes in the environment, Anr may play a significant role in global Sb cycling in both marine and terrestrial environments.
sp. 菌株 SVR 利用锑酸盐 [Sb(V)] 作为厌氧呼吸的末端电子受体。在这里，我们通过活性染色和非变性凝胶电泳来可视化可能的关键酶——周质 Sb(V) 还原酶（Anr）。液相色谱-串联质谱分析显示，一种新型二甲基亚砜（DMSO）还原酶家族蛋白 WP_173201954.1 参与了 Anr。该蛋白与 AnrA 密切相关，AnrA 被认为是 中呼吸 Sb(V) 还原酶的催化亚基。菌株 SVR 的 基因形成了一个操纵子样结构，并且它们的转录在 Sb(V) 呼吸条件下被上调。 基因的表达被超过 1 µM 的锑[Sb(III)]诱导；然而，砷酸盐 [As(III)] 并没有诱导 基因的表达。基于串联质量标签的蛋白质组学分析表明，除了 Anr 蛋白外，在 Sb(V) 呼吸条件下，以下类别的蛋白质也被上调：(i) Sb(III) 外排系统，如 Ant 和 Ars；(ii) 抗氧化蛋白，如铁蛋白、Rubredoxin 和硫氧还蛋白；(iii) 蛋白质质量控制系统，如 HspA、HslO 和 DnaK；和 (iv) DNA 修复蛋白，如 UspA 和 UvrB。这些结果表明，菌株 SVR 通过调节多种过程来抵抗和主动代谢锑来应对锑胁迫。据我们所知，这是首次证明 AnrA 参与 Sb(V) 呼吸的蛋白质水平的报告。此外，这是第一个显示 Sb(V) 呼吸细菌中 Ant 系统蛋白高表达的例子。
锑 (Sb) 在环境中主要以亚锑酸盐 [Sb(III)] 或锑酸盐 [Sb(V)] 形式存在，而 Sb(III) 比 Sb(V) 毒性更大。最近，微生物参与 Sb 氧化还原反应引起了人们的关注。尽管已经报道了超过 90 种 Sb(III) 氧化细菌，但关于 Sb(V) 还原细菌的信息有限。特别是，尽管该途径对于 Sb 在自然界中的循环非常重要，但参与异化 Sb(V) 还原或 Sb(V) 呼吸的酶仍不清楚。在这项研究中，我们证明了 Sb(V) 还原酶（Anr）是一种 Sb(V) 呼吸细菌（ sp. SVR）的新型二甲基亚砜（DMSO）还原酶家族成员。此外，我们发现菌株 SVR 通过调节包括 Ant 和 Ars 系统在内的多种过程以及上调抗氧化和质量控制蛋白水平来应对 Sb 胁迫。考虑到环境中假定的 基因的丰富度和多样性，Anr 可能在海洋和陆地环境中都对 Sb 的全球循环起着重要作用。
