Identification of Propionate-Degrading Microbial Populations in Methanogenic Processes for Waste Treatment: Methanosaeta and Methanoculleus

Methanogenic processes have great potential in the sustainable treatment of organic wastes with the production of methane as a renewable source of energy. However, the broader application of methanogenic processes has been hindered by process instability frequently encountered during fluctuations in operational conditions. The accumulation of organic acids, particularly propionate, is considered to be an important cause of process instability. Therefore, to gain an understanding of microbial responses during process instability, it is imperative to identify microbial populations involved in the utilization of elevated levels of propionate. In this study, microbial community analysis showed that bacterial populations from the orders of Syntrophobacterales and Clostridiales were the primary syntrophic partners in anaerobic conversion of propionate. Archaeal populations associated with Methanosaeta and Methanoculleus dominated the propionate-degrading communities enriched in methanogenic batch bioreactors. The involvement of Methanosaeta and Methanoculleus in anaerobic conversion of propionate was further supported by the close correspondence between elevated propionate and increased population abundance of Methanosaeta and Methanoculleus in continuous anaerobic digesters treating animal waste. Subsequent testing using additional methanogenic batch bioreactors revealed that the dominance of Methanosaeta and Methanoculleus populations was linked to the anaerobic degradation of elevated levels of propionate and butyrate, but not the conversion of formate, acetate, or methanol into methane. The identification of microbial populations specifically linked to anaerobic conversion of elevated propionate in this study provided much needed insight for the understanding of microbial processes relevant to process stability in methanogenic waste treatment.