Lignin and Peptide Promote the Abundance and Activity of Arsenic Methylation Microbes in Paddy Soils

Rice physiological straighthead disease is induced by microbially mediated arsenic methylation and usually regionally distributed in paddy soils. However, the biogeochemical mechanism underlying the geographic distribution of microbial communities harboring methylating genes (arsM) remains unclear. Herein, we revealed significant (p = 0.001) differences in the arsM communities in different regions of Chinese paddy soils at the continental scale. Moreover, a positive correlation between the diversity of arsM communities and the chemodiversity of soil dissolved organic matter (DOM) was revealed. Among the different DOM components, lignin- and peptide-like DOM are the most important DOM components impacting the abundance and diversity of arsM communities. Metatranscriptomic analyses of 18 selected paddy soil samples revealed that the expression of the arsM gene increased with increasing soil lignin and peptide contents. Compared with the control, the addition of lignin and peptide significantly (p < 0.05) increased the methylated As concentration in the incubated paddy soils. Communities harboring arsM genes belonging to the phyla Chloroflexota, Verrucomicrobiota, Deltaproteobacteria, Thermodesulfobacteriota, and Ignavibacteriota mostly dominated in paddy soils with relatively high lignin and peptide contents. This study highlights the correlation between the diversity of DOM and arsM communities in paddy soils and provides mechanistic information for soil arsenic contamination control and sustainable rice production.