Abstract: The effect of exogenous arsenate (As(Ⅴ)) input on the anaerobic fermentation and community structure in situ in arsenic (As)-contaminated sediments was investigated to elucidate the interaction between As(V) and microbial community composition in the arsenic-contaminated estuarine sediments. The As-contaminated sediments were collected from the Wuli River in Huludao City, Liaoning Province, China. The sediment samples were incubated after adding As(V) (i.e., 1, 10, 60 mg·L^-1, respectively). Physicochemical parameters (e.g., hydrogen production, acid production, pH, and carbon consumption) and microbial community composition were measured during incubation. The dominant strains were isolated from culture solution with high As(V) concentration using plate dilution method. During the enrichment culture, transformation of arsenic form was observed in all treatments. Among them, about 43% of As(V) was converted to arsenite (As(Ⅲ)) in the treatment with 60 mg·L^-1 As(V). At the end of the incubation, the phylum number in the original sediment decreased from eleven to one (Firmicutes), and the dominant genus Clostridium_sensu_stricto_1 occupied the dominant ecological niche. An anaerobic fermentative Clostridium butyricum CXL-1 with the high As(Ⅲ) tolerance (≥200 mg·L^-1) was isolated from the treatment with the addition of 60 mg·L^-1 As(V), which showed the capacity to produce fermentation products such as organic acids and H₂ by glucose fermentation metabolism, thereby providing hydrogen and carbon sources for sulfate-reducing bacteria and methanogens. Our results can provide reference for the anaerobic mineralization remediation of As-contaminated environments by microorganisms.

Key words: arsenic contamination, anaerobic fermentation, sediment, microbial diversity, Clostridium butyricum CXL-1