Bacterial succession in an abandoned circum-neutral opencast coal mine in India

ContextAbandoned mines provide an ideal opportunity to study the succession of microbial communities, which is crucial for the development and stability of the soil.AimsWe examined the diversity and temporal succession of the microbial community in an abandoned coal mine.MethodsWe investigated soil geochemical parameters and microbial succession using high-throughput 16S rRNA gene amplicon sequences over a 4-year period in a derelict opencast circum-neutral coal mine in Tasra colliery, Jharkhand, India.ResultsSoil pH (4.46-6.13), organic carbon (0.86-4.53%), available nitrogen (0.001-0.003%) and total cultivable heterotrophic microbial load increased, and concentrations of chloride (24 865-15 067 ppm), sulfate (26 417-417 ppm) and heavy metals reduced over the period of 4 years. The 16S rRNA gene sequences identified Proteobacteria as the dominant phylum across samples except for the fourth year, where Actinobacteria was predominant. Chlorobi, WPS-2 and Spirochaetes were exclusively identified in the first year. Twelve phyla present in the first year were completely absent by the end. In the fourth year, an abundance of nitrogen-fixing members such as Burkholderiales, Rhizobiales, Roseiflexales and Actinomycetales was noted and semi-quantitative PCR suggested that nitrogenases were predominately vanadium dependent (relative to molybdenum). Gradual shifts from purportedly chemolithotrophic to heterotrophic metabolic strategies were also observed.ConclusionThis work establishes that soil improvement in abandoned coal mines involves the dynamic interplay of physicochemical parameters and shifts in microbial communities and dominant metabolic guilds. This knowledge can be used to plan and monitor remediation measures in such sites. The present work studies microbial diversity and community shift using high-throughput, bar-coded sequencing of 16S rDNA amplicons in an abandoned open-cast coal mine along a temporal scale, to show how natural succession is dependent on shift in metabolic choices of the soil bacterial population. This knowledge of bidirectional influence of microbial population and physicochemical parameters in an abandoned coal mine can be used to plan remediation measures.