Characterization of As(III)-oxidizing bacteria Acinetobacter sp. TMKU7 having plant growth promoting features for possible application in arsenic-contaminated crop field

Abstract

Arsenic pollution is considered as one of the global environmental threats. Arsenic is found in nature mostly in two different valence states, namely arsenite [As(III)] and arsenate [As(V)], the former is more toxic due to its solubility and reactivity. Certain microbial communities inhabiting in the As-rich environment contribute a lot in the geochemical cycling of As. This study focuses on the isolation and identification of As(III) oxidizing bacteria from soil sample, and furthermore assessment of its As(III) transforming potential. The study was also aimed to hunt its plant growth promoting features for possible application to promote crop yield As-contaminated soil. Among the 28 bacterial isolates, a strain designated as TMKU7 could transform ∼80% As(III) to As(V) under culture condition. Based on morphological, biochemical, and molecular characterization, the strain was identified as Acinetobacter sp. Arsenite oxidase, the key player for As(III) to As(V) conversion was found to be constitutive in this strain, and the enzymatic activity was mostly found in the periplasmic fraction. The K m and V max of the partially purified As(III) oxidase were determined to be 41.43 μM and 0.19 μM min−1 μg−1 protein, respectively. The presence of As(III) oxidase gene (aioA) in the genomic DNA was further confirmed by PCR amplification. Agarose entrapped partially purified enzyme showed a potential for As(III) removal from water as well. The expression of various plant growth promoting traits have added additional importance to this As-resistant strain, which could be utilized as a prospective As-detoxification candidate in the As-contaminated crop field for sustainable agriculture.