Correlation of bacterial communities supported by different organic materials with sulfate reduction in metal-rich landfill leachate

► Five materials tested for their suitability for use in passive bioremediation processes for supporting sulfate reducers and sulfate reduction were ranked silage > compost = molasses/hay > cattails > pulp mill biosolids. ► Of all of the bulk material properties measured the only correlation that we found was an increase of SRR and SRB numbers with C/N ratio. ► The bacterial community associated with degradation of complex organic matter was found to be comprised of microbes related to Cytophaga sp., Clostridia, Fibrobacteres, and Spirochaetes. ► Using a survey of the dsr gene, likely sulfate reducers in the materials included Desulfovibrio sp., Desulfonema sp., Desulfomicrobium sp., and Desulfotomaculum sp., in order of importance, with lesser amounts of other genera also present. ► The material, silage, that achieved the highest SRR and supported the most SRB, had a SRB community structure that was different from those for other materials also supporting sulfate reducers in the same environment, showing that there is a correlation between bacterial community and sulfate reduction rate.