Soil Microbiome and its Functional Attributes Under the Gradient of Arsenic Contamination in Paddy Soils

Abstract

The build-up of arsenic in agricultural soil through contaminated irrigational groundwater is a concern. Metagenomic analysis of such contaminated sites may provide a remarkable opportunity to extensively investigate the responses and adaptation of microbial communities to different levels of arsenic. The study focuses on the comparative analysis of microbial community composition and associated functions in paddy soil samples with a gradient of arsenic contamination (4.88 to 43.67 mg kg-1). Actinobacteria was found to dominate the bacterial phyla in all four samples with abundance ranging from 39.77% to 49.39% followed by Proteobacteria (20.71-38.24%). Whereas the fungal phylum Ascomycota (92.42-95.29%) dominated all the samples studied. In the study, bacteria were found to be abundant in the mid-level (15.89 and 24.84 mg kg-1) of arsenic, which included genera Gaiella, Nocardioides, Solirubrobacter, Microvirga, and Nitrospira. Fungi Beauveria, Talaromyces, Aspergillus, Pyrenophora, and Valsa were higher in relative abundance corresponding to soil arsenic concentration. Verticillium, previously reported for Pb, Zn, and Cd removal, was found in the soil sample with the mid-arsenic concentration (15.89 mg kg-1). The relative abundance of the arsenic metabolizing/ transport genes of native microbial communities also varied with the soil arsenic gradient, the genes arsJ, arsM, aioR, arsH, and arsC being the most affected. The study is the first report of Gaiella, Solirubrobacter, Beauveria, and Verticillium present in arsenic-contaminated soil, and further studies are required to explore their potential role in arsenic bioremediation.