Mercury tolerance and bioremediation potential of mountain soil bacteria: Insights from Darjeeling, containing elevated levels of mercury

More and more research is now being focused on the mercury contamination of remote mountain environments. This study aimed to explore the mountain soil of Tiger Hill, Darjeeling, through the lens of its mercury tolerant bacterial microbiome to characterize regional mercury pollution and isolate strains with mercury bioremediation potential. The soil bacteria isolated from the region displayed an extreme tolerance to mercury at previously unseen levels of up to 7 mg/mL. The mercury removal capacity of the two best isolates, MTD11C and MTD11E, identified as strains of Brevundimonas naejangsanensis and Staphylococcus arlettae, exhibited a mercury removal capacity of 99.74 % and 99.56 %, respectively. As per our research, such extreme tolerance to mercury as demonstrated by the bacterial strains has not been reported thus far. The prevalence of such tolerance in the microbiota of a region may well be an indication of the degree of mercury pollution harbored by it. Their tolerance to other heavy metals and antibiotics, as well as active plant growth promotion traits, were also characterized in this study. The topsoil of this region was estimated to contain elevated levels of mercury at around 0.52-2.39 mg kg^-1. Ecological risk assessment further showed the potential for harm to the environment posed by the level of mercury. Collected vegetation samples from tea plantations surrounding Tiger Hill displayed an accumulation of mercury in the leaves and roots of the tea plants as well, suggesting rampant mercury pollution that needs to be addressed.