Arsenic contamination influences microbial community structure and putative arsenic metabolism gene abundance in iron plaque on paddy rice root.

Iron (Fe) plaque on rice roots contains a unique microbiota that connects the root and rhizosphere environments. However, the factors controlling the microbial community structure and function in Fe plaque are unknown. We performed Illumina sequencing of 16S rRNA gene amplicons and of total community DNA to compare the microbial community structure and metabolic potential of Fe plaques derived from arsenic (As)- and non-contaminated sites. Geobacter and Hydrogenophaga were identified as the genera that differed significantly in abundance between As-contaminated and control samples (P < 0.05). Significant differences were found between contaminated and control samples in the relative abundances of predicted As functional genes of the microbial community in Fe plaque, in which the relative abundances of the arsC (encoding As(V) reductase) and arsB genes (encoding As(III) efflux membrane protein) in Fe plaque from contaminated sites (YH and TP samples) were significantly higher than those from the control samples (P < 0.05). In addition, the As concentration in Fe plaque contributed significantly to the relative abundance of genes related to As metabolism and correlated most strongly with the abundance of arrB genes (encoding respiratory arsenate reductase, FeS subunit). These results suggest that As contamination influences the community structure and metabolic potential of Fe plaque-associated microorganisms and may help in understanding the environmental behavior of As at the interface of Fe plaque.