Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ 85721, USA.
Appl Environ Microbiol. 2010 Oct;76(20):6804-11. doi: 10.1128/AEM.00734-10. Epub 2010 Aug 20.
Microorganisms play a significant role in the speciation and mobility of arsenic in the environment. In this study, the oxidation of arsenite [As(III)] to arsenate [As(V)] linked to chlorate (ClO₃⁻) reduction was shown to be catalyzed by sludge samples, enrichment cultures (ECs), and pure cultures incubated under anaerobic conditions. No activity was observed in treatments lacking inoculum or with heat-killed sludge, or in controls lacking ClO₃⁻. The As(III) oxidation was linked to the complete reduction of ClO₃⁻ to Cl⁻, and the molar ratio of As(V) formed to ClO₃⁻ consumed approached the theoretical value of 3:1 assuming the e⁻ equivalents from As(III) were used to completely reduce ClO₃⁻. In keeping with O₂ as a putative intermediate of ClO₃⁻ reduction, the ECs could also oxidize As(III) to As(V) with O₂ at low concentrations. Low levels of organic carbon were essential in heterotrophic ECs but not in autotrophic ECs. 16S rRNA gene clone libraries indicated that the ECs were dominated by clones of Rhodocyclaceae (including Dechloromonas, Azospira, and Azonexus phylotypes) and Stenotrophomonas under autotrophic conditions. Additional phylotypes (Alicycliphilus, Agrobacterium, and Pseudoxanthomonas) were identified in heterotrophic ECs. Two isolated autotrophic pure cultures, Dechloromonas sp. strain ECC1-pb1 and Azospira sp. strain ECC1-pb2, were able to grow by linking the oxidation of As(III) to As(V) with the reduction of ClO₃⁻. The presence of the arsenite oxidase subunit A (aroA) gene was demonstrated with PCR in the ECs and pure cultures. This study demonstrates that ClO₃⁻ is an alternative electron acceptor to support the microbial oxidation of As(III).
微生物在环境中砷的物种形成和迁移中起着重要作用。在这项研究中，证明了在厌氧条件下培养的污泥样品、富集培养物（ECs）和纯培养物可以催化亚砷酸盐[As(III)]氧化为砷酸盐[As(V)]，同时伴随着氯酸盐（ClO₃⁻）的还原。在没有接种物或使用热灭活污泥的处理中，或在没有 ClO₃⁻的对照中，没有观察到活性。As(III)的氧化与 ClO₃⁻的完全还原为 Cl⁻有关，形成的 As(V)与消耗的 ClO₃⁻的摩尔比接近 3:1 的理论值，假设 As(III)的电子当量用于完全还原 ClO₃⁻。与 O₂ 作为 ClO₃⁻还原的假定中间产物一致，ECs 也可以在低浓度的 O₂ 下将 As(III)氧化为 As(V)。在异养 ECs 中，低水平的有机碳是必不可少的，但在自养 ECs 中则不是。16S rRNA 基因克隆文库表明，ECs 在自养条件下主要由 Rhodocyclaceae（包括 Dechloromonas、Azospira 和 Azonexus 型）和 Stenotrophomonas 的克隆组成。在异养 ECs 中还鉴定出了其他的型（Alicycliphilus、Agrobacterium 和 Pseudoxanthomonas）。两株分离的自养纯培养物，Dechloromonas sp. strain ECC1-pb1 和 Azospira sp. strain ECC1-pb2，能够通过将 As(III)氧化为 As(V)与 ClO₃⁻的还原相连接来生长。在 ECs 和纯培养物中，通过 PCR 证明了亚砷酸盐氧化酶亚基 A (aroA)基因的存在。本研究表明，ClO₃⁻是一种替代电子受体，可以支持微生物对 As(III)的氧化。
