Investigation of Methanosarcinales and Methanomicrobiales Presence within a Dry Anaerobic Digester

Greenhouse gasses such as methane and carbon dioxide are thought to play a major role in global climate change. Anaerobic digesters function to produce energy using the methane derived from organic matter which would typically be deposited in landfills. The three main types of digesters are low-solids wet digesters, high-solids wet digesters, and dry anaerobic digesters. Dry anaerobic digesters are drastically rarer than wet digesters, and the microbial community responsible for the production of biogas is consequently less-studied than in other types of digesters. In this study, the 16S rRNA gene copy concentrations of Methanosarcinales spp. and Methanomicrobiales spp. were determined using qPCR during a 28-day fermentation cycle. Biogas analysis showed that fermenters with an added carbon source, microcrystalline cellulose, produced a greater volume of biogas and methane than those without substrate. At each point in the 28-day fermentation, Methanosarcinales spp. were present at approximately 10 7 16S rRNA genes per gram of sample, whereas Methanomicrobiales spp. had concentrations between 10 4 and 10 6 16S genes per gram of sample. Overall, Methanosarcinales spp. were consistently more abundant at every tested time point. The different concentrations of methanogens could indicate that the nutrients and conditions within the tested digester are more suited to the metabolism of Methanosarcinales spp. than Methanomicrobiales spp. This information helps to fill the knowledge gap concerning methanogen presence in dry anaerobic digesters, and could be used in the future to dictate the type of substrate used in a particular dry anaerobic digester.