The duality of sulfate-reducing bacteria: Reducing methylmercury production in rhizosphere but enhancing accumulation in rice plants

• Published in: Journal of hazardous materials 2024-09, Vol.476, p.135049, Article 135049
• Main Authors: Guo, Pan, Du, Hongxia, Mao, Qiaozhi, Deng, Yuhan, Wang, Xun, Li, Jing, Xiong, Bingcai, Fan, Xu, Wang, Dingyong, Agathokleous, Evgenios, Ma, Ming
• Format: Article
• Language: English
• Subjects: Amino acid; Bacteria - metabolism; Biodegradation, Environmental; Methylmercury; Methylmercury Compounds - metabolism; Oryza - growth & development; Oryza - metabolism; Oryza - microbiology; Plant Roots - metabolism; Plant Roots - microbiology; Rhizosphere; Rice; Soil Microbiology; Soil Pollutants - metabolism; Sulfate-reducing bacteria; Sulfates - metabolism; Sulfur-Reducing Bacteria - metabolism; Transcription factors
• ISSN: 0304-3894; 1873-3336; 1873-3336
• DOI: 10.1016/j.jhazmat.2024.135049

Sulfate-reducing bacteria (SRB) are known to alter methylmercury (MeHg) production in paddy soil, but the effect of SRB on MeHg dynamics in rhizosphere and rice plants remains to be fully elucidated. The present study investigated the impact of SRB on MeHg levels in unsterilized and γ-sterilized mercury-polluted paddy soils, with the aim to close this knowledge gap. Results showed that the presence of SRB reduced MeHg production by ∼22 % and ∼17 % in the two soils, but elevated MeHg contents by approximately 55 % and 99 % in rice grains, respectively. Similar trend at smaller scales were seen in roots and shoots. SRB inoculation exerted the most profound impact on amino acid metabolism in roots, with the relative response of L-arginine positively linking to MeHg concentrations in rhizosphere. The SRB-induced enrichment of MeHg in rice plants may be interpreted by the stronger presence of endophytic nitrogen-related microbes (e.g. Methylocaldum, Hyphomicrobium and Methylocystis) and TGA transcription factors interacting with glutathione metabolism and calmodulin. Our study provides valuable insights into the complex effects of SRB inoculation on MeHg dynamics in rice ecosystems, and may help to develop strategies to effectively control MeHg accumulation in rice grains. [Display omitted] •SRB inoculation mitigated MeHg production in rhizosphere soil.•SRB inoculation facilitated MeHg enrichment in rice.•Endophytic nitrogen-related microbes could promote MeHg accumulation in rice.•TGA transcription factor could boost MeHg accumulation in rice.•L-arginine can be deemed as the indicator for soil MeHg concentrations.