Characterization and exploration of an As(III)-oxidizing bacterium TMKU1 for plant growth promotion under arsenic stress

Abstract

Arsenic (As) pollution has been recognized as a serious global environmental problem. Though various remediation strategies are being explored to cope up with the As-toxicity, currently microbe-assisted detoxification of As is found to be the most promising technique for restoring As-contaminated rhizosphere soil for its eco-friendly nature. As(III)-oxidizing bacteria were reported to most suitable in this regard. In this study, an As(III)-oxidizing bacterium, TMKU1 was isolated from As-contaminated rhizospheric soil that could withstand up to 20 mM As(III) and 95 mM As(V). The strain was closely related to the genus Acinetobacter, according to 16 S rDNA analysis. The strain could transform ∼70% of As(III) to As(V) under aerobic culture condition. The transformation of As(III) was found to be catalyzed by arsenite oxidase, which is constitutive nature in this strain. The As(III)-oxidase was found to be encoded by the functional gene aioA harbored on the genomic DNA. The enzyme was localized mostly in the periplasm, and the partially purified enzyme showed the Km = 95.76667 μM and Vmax = 0.356341 M min−1g−1 protein. The novelty of this strain is that it could express plant growth promoting features like phosphate solubilization, siderophore production, IAA production and N2-fixation, both under stress-free and As-stress conditions. Seed bacterization with TMKU1 not only significantly increased the germination of chickpea seeds, but also shielded the seedlings from the As toxicity and accumulation. Overall, the results suggest that this bacterial candidate would be of potential use in agricultural practices for detoxification of As in crop field.