Abstract
Microbial arsenite oxidation is an essential biogeochemical process whereby more toxic arsenite is oxidized to the less toxic arsenate. Thiomonas strains represent an important arsenite oxidizer found ubiquitous in acid mine drainage. In the present study, the arsenite oxidase gene (aioBA) was cloned from Thiomonas delicata DSM 16361, expressed heterologously in E. coli and purified to homogeneity. The purified recombinant Aio consisted of two subunits with the respective molecular weights of 91 and 21 kDa according to SDS-PAGE. Aio catalysis was optimum at pH 5.5 and 50–55 °C. Aio exhibited stability under acidic conditions (pH 2.5–6). The Vmax and Km values of the enzyme were found to be 4 µmol min−1 mg−1 and 14.2 µM, respectively. SDS and Triton X-100 were found to inhibit the enzyme activity. The homology model of Aio showed correlation with the acidophilic adaptation of the enzyme. This is the first characterization studies of Aio from a species belonging to the Thiomonas genus. The arsenite oxidase was found to be among the acid-tolerant Aio reported to date and has the potential to be used for biosensor and bioremediation applications in acidic environments.
Highlights
Arsenite oxidase catalyzes the oxidation of arsenite to arsenate by a two-electron transfer
Arsenite oxidase consists of two heterologous subunits; a large catalytic subunit (AioA) with bis-molybdopterin guanine dinucleotide cofactor and a 3Fe-4S iron sulfur cluster, and a small subunit (AioB) with Rieske 2Fe-2S center
Arsenite oxidizing bacteria have been isolated from diverse arsenic contaminated environments, such as cattledipping fluids, hot springs, mine tailing and drainage water
Summary
Arsenite oxidase catalyzes the oxidation of arsenite to arsenate by a two-electron transfer. Arsenite oxidase is a member of the dimethylsulfoxide (DMSO) reductase family of molybdoenzyme which is a family of different prokaryotic redox enzymes that function in electron transport chain (Romao 2009). Arsenite oxidizing bacteria have been isolated from diverse arsenic contaminated environments, such as cattledipping fluids, hot springs, mine tailing and drainage water. As an ancient bioenergetic enzyme which utilizes arsenite, a highly toxic metalloid as substrate, characterization of arsenite oxidase is of special interest for bioremediation and biosensor construction. Both bacteria grow optimally at slightly alkaline pH 8, which can be categorized as alkaline-tolerant bacteria.
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