Soil humic substances-specific diversity and functional traits of arsenic-reducing bacteria in flooded paddy soil

Humic substances represent a key component of organic matter in soil and can strikingly activate metal-reducing microorganisms to promote microbial arsenic release in flooded paddy soil. Despite its recognized importance, the fundamental question of whether and how soil humic fractions selectively affects the assembly of arsenic-reducing soil microbiota in native soil system remain underexplored. In this study, first, we established anaerobic soil microcosms amended with different soil-derived humic fractions, including soil fulvic acid, humic acid, and humin fractions to probe the variability in microbial arsenic reduction facilitated by different soil humic fractions. Next, we aim to investigate temporal variability in the diversity and composition of potential arsenic-related soil microbiomes responsive to soil humic substances and, more importantly, to enrich those microbial communities through the soil-resupplying enrichment approach by reinoculation of microbial subcultures in their native, but sterilized soil to facilitate their recolonization. At last, genome-resolved metagenomics was applied to profile and compare community-level variability in functional traits in response to different soil humic fractions, with emphasis on the coupling between arsenic biotransformation and other elemental cycles. Deciphering the underlying linkage between soil humic substances and arsenic biogeochemical cycling is beneficial to target remediation and food safety in rice paddy field.