Role of cost-effective organic carbon substrates in bioremediation of acid mine drainage-impacted soil of Malanjkhand Copper Project, India: a biostimulant for autochthonous microbial populations.

Development of an efficient bioremediation strategy for the mitigation of low pH (3.21), high dissolved SO (6285 mg/L), and Fe (7292 mg/kg)-rich acid mine drainage-impacted soil (AIS) was investigated through amendment of readily available organic carbon substrates (rice husk, compost, leaf litter, and grass clippings). An organic carbon mixture (OCM) formulated by mixing the test substrates was used to biostimulate microbial processes (SO/Fereduction) necessary for efficient attenuation of the hazards imposed by AIS. OCM amendment in calcium carbonate-treated AIS enhanced reductive processes and removed dissolved SO and Fe considerably raising the pH close to neutrality. 16S rRNA gene amplicon sequencing performed with total DNA and RNA elucidated the microbial population dynamics of treated AIS. Metabolically active populations comprised of fermentative (Clostridium sensu stricto 1 and Fonticella), iron-reducing (Acidocella, Anaeromyxobacter, and Clostridium sensu stricto 1), and sulfate-reducing (Desulfovibrio, Desulfotomaculum, Desulfosporosinus, and Desulfobacteraceae) bacteria. Microbial guilds obtained highlighted the synergistic role of cellulolytic, fermentative, and SO/Fe-reducing bacteria in attenuation of hazardous contaminants. Quantitative PCR analysis well supported the role of OCM in stimulating the indigenous bacterial populations, including those harboring the dissimilatory sulfite reductase (dsrB) gene and involved actively in SO reduction. The study demonstrated the suitability of locally available organic substrates as a low-cost and efficient biostimulation agent for in situ bioremediation of acid mine drainage (AMD)-impacted soil system.