Depth-dependent microbial communities potentially mediating mercury methylation and various geochemical processes in anthropogenically affected sediments

• Published in: Environmental research 2023-11, Vol.237, p.116888-116888, Article 116888
• Main Authors: Kumar Chaudhary, Dhiraj, Bajagain, Rishikesh, Seo, DongGyun, Hong, Yongseok, Han, Seunghee
• Format: Article
• Language: English
• Subjects: Bacteroidetes; Biogeochemical cycles; Chloroflexi; Firmicutes; Functional genes; geochemistry; mercury; Mercury-contamination; methanogens; Methanosarcina; methylation; Methylmercury; methylmercury compounds; microbial communities; Microorganisms; sediments; Thauera; Trace metals
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1016/j.envres.2023.116888

Metal contamination and other geochemical alterations affect microbial composition and functional activities, disturbing natural biogeochemical cycles. Therefore, it is essential to understand the influences of multi-metal and geochemical interactions on microbial communities. This work investigated the distributions of total mercury (THg), methylmercury (MeHg), and trace metals in the anthropogenically affected sediment. The microbial communities and functional genes profiles were further determined to explore their association with Hg-methylation and geochemical features. The levels of THg and MeHg in sediment cores ranged between 10 and 40 mg/kg and 0.01–0.16 mg/kg, respectively, with an increasing trend toward bottom horizons. The major metals present at all depths were Al, Fe, Mn, and Zn. The enrichment and contamination indices confirmed that the trace metals were highly enriched in the anthropogenically affected sediment. Various functional genes were detected in all strata, indicating the presence of active microbial metabolic processes. The microbial community profiles revealed that the phyla Proteobacteria, Bacteroidetes, Bathyarchaeota, and Euryarchaeota, and the genera Thauera, Woeseia, Methanomethylovorans, and Methanosarcina were the dominant microbes. Correlating major taxa with geochemical variables inferred that sediment geochemistry substantially affects microbial community and biogeochemical cycles. Furthermore, archaeal methanogens and the bacterial phyla Chloroflexi and Firmicutes may play crucial roles in enhancing MeHg levels. Overall, these findings shed new light on the microbial communities potentially involved in Hg-methylation process and other biogeochemical cycles. [Display omitted] •patial and vertical variations of THg, MeHg, and trace metals were identified.•EF, CF, Igeo, DC, and PLI indexes showed high degree of metal enrichment.•Microbial compositions and functional genes are correlated with geochemical variability.•Archaeal methanogens might be efficient as SRB group in driving Hg-methylation.•The metabolisms and biogeochemical roles of keystone microbes have been portrayed.