The Diversity and Resistance of Microbial Community under Mercury Contamination in Paddy Soils

Traditional gold mining may cause mercury pollution in rice fields, resulting in a significant decrease in rice grain yields, as well as socio-economic and health issues. Bioremediation using indigenous microbes is a promising method to alleviate mercury contamination. Thus, it is necessary to explore the diversity and ability of microbes to remediate the contamination. This study investigated the indigenous microbes in mercury-contaminated soils collected from paddy fields around a gold mining area in Sukabumi Regency, Indonesia. Six soil samples were collected from three locations at the dry season; two paddy fields and a tailing pond located next to gold amalgamation machinery. Physicochemical analysis and total mercury concentration measurement of the soil samples were performed immediately after sampling. Bacteria in soil samples were cultured on Nutrient Agar and its colonies were counted after 24 hours of cultivation. Morphological characterization of the colonies was observed under a light microscope. Bacterial community composition was investigated using 16S rRNA amplicon sequencing. The resistance of bacteria to the mercury was tested by inoculating the mixed cultures in Mueller-Hinton agar supplemented with HgCl2 in concentrations of 10, 30, and 50 ppm. Bacterial colonies appeared higher in the soil sample with the lowest total mercury concentration. However, microbial community compositions were more diverse in the soil with medium mercury contamination. Furthermore, the microbial community cultured from tailing soil, despite lower bacterial diversity, performed mercury resistance up to 50 ppm. Upcoming studies should be conducted to investigate further potential indigenous microbial communities for reducing mercury contamination in soils.