Toward Understanding the Physiological Determinants of Microbial Competitiveness in Methanogenic Processes

Methanogenesis is of great significance in both natural and engineered processes. Anaerobic digestion technology represents the engineering-scale implementation of methanogenesis in waste treatment processes. Despite the broad application of anaerobic digestion as a common waste treatment option, much remains to be learned on the anaerobic food web underlying methanogenesis for more effective process modeling and control.

Following an initial screening of various substrates, six continuous lab-scale anaerobic digesters were developed with animal waste as the substrate. The linkage between microbial community composition and process performance was studied by initiating process imbalance with organic overloading. As a result, accumulation of short chain fatty acids, particularly acetate, occurred in response to the onset of process imbalance. Populations related to Methanosaeta vastly outnumbered those of Methanosarcina as the dominant acetoclastic methanogen throughout the study period, even at elevated acetate concentrations during process imbalance, which is unexpected as it is considered that Methanosaeta can out-compete Methanosarcina only at low acetate concentrations, typical for balanced anaerobic food webs. Subsequent methanogenic batch cultures enriched with high concentrations of acetate further confirmed the dominance of Methanosaeta over Methanosarcina. Given the significance of acetoclastic methanogenesis in the anaerobic food web and global carbon cycling, it is evident that the interactions between Methanosaeta and Methanosarcina need to be better defined. Other novel microbial populations were also identified as abundant constituents of the microbial communities in the anaerobic digesters, including populations related to Crenarchaeota. It is critical to understand the roles these abundant but poorly-described populations play in the anaerobic food web.