Quantitative Analysis of Methangenic Community in Anaerobic Digesters and its Response to Freeze Drying and Exposure to Oxygen

Methanogens are integral to carbon cycling, catalyzing the production of methane and carbon dioxide, both potent greenhouse gases. Methane is produced in a wide variety of highly reduced anaerobic environments, as well as by degradation of organic compounds in industrial and municipal wastewater. This process is carried out by the concerted activity of an interdependent microbial community, composed of Bacteria and Archaea, the later including methanogens which complete the final step and produce methane and carbon dioxide. Methanogenesis is often the rate limiting step and is sensitive to processing imbalances. Therefore, an understanding of the microbial community structure and dynamics in anaerobic process is a basic requirement to optimize anaerobic digestion for increased renewable energy production. To examine the relationship between methane production and methanogen community structure, quantitative polymerase chain reaction (qPCR) was used to quantify the total methanogen community (mcrA gene) as well as specific genera (16S rRNA gene) in biomass from industrial scale digesters. Results from this study revealed that there was a positive correlation between methane production and mcrA and Methanospirillum transcripts. It was also found that reactors not dominated by any particular genus, but those that had a balanced community of hydrogenotrophic and aceticlastic methanogens had a higher capacity to resist organic overload and produce methane. One of the major problems faced in anaerobic digestion process is its inherent instability and sensitivity to frequent exposure to oxygen. qPCR analyses of 16S rRNA revealed that Methanoculleus had significantly lower activity, while Methanospirillum and Methanosaeta had significantly higher activity at higher oxygen concentrations. Finally, this study also presents the use of freeze drying as a viable method for preserving anaerobic methanogenic biomass. qPCR with 16S rRNA genus specific primers revealed that methanogens varied in their ability to tolerate the process of freeze drying. Methanospirillum had the highest 16S rRNA transcripts before and after drying, followed by Methanosaeta and Methanoculleus. Therefore, the data obtained from this study helps to determine the identity of desirable organisms and community architecture in relation to digester performance, exposure to oxygen and low temperature desiccation encountered during preservation by freeze drying

Relating Methanogen Community Structure and Anaerobic Digester Function

Much remains unknown about the relationships between microbial community structure and anaerobic digester function. However, knowledge of links between community structure and function, such as specific methanogenic activity (SMA) and COD removal rate, are valuable to improve anaerobic bioprocesses. In this work, quantitative structure–activity relationships (QSARs) were developed using multiple linear regression (MLR) to predict SMA using methanogen community structure descriptors for 49 cultures. Community descriptors were DGGE demeaned standardized band intensities for amplicons of a methanogen functional gene (mcrA). First, predictive accuracy of MLR QSARs was assessed using cross validation with training (n = 30) and test sets (n = 19) for glucose and propionate SMA data. MLR equations correlating band intensities and SMA demonstrated good predictability for glucose (q2 = 0.54) and propionate (q2 = 0.53). Subsequently, data from all 49 cultures were used to develop QSARs to predict SMA values. Higher intensities of two bands were correlated with higher SMA values; high abundance of methanogens associated with these two bands should be encouraged to attain high SMA values. QSARs are helpful tools to identify key microorganisms or to study and improve many bioprocesses. Development of new, more robust QSARs is encouraged for anaerobic digestion or other bioprocesses, including nitrification, nitritation, denitrification, anaerobic ammonium oxidation, and enhanced biological phosphorus removal

Activity of Methanogenic Biomass After Heat and Freeze Drying in Air

It would be beneficial if methanogenic cultures could be preserved for anaerobic digester bioaugmentation or as seed for standard tests such as biochemical methane potential. However, storage of wet culture or drying in anaerobic atmosphere may not be economically feasible. In this study, the effect of heat and freeze drying in ambient air on the methanogenic activity of an anaerobic culture was determined. The anaerobic culture was dried in air at 104 °C for 12 h, and by freezing at −196 °C in air with subsequent drying at subzero temperatures. The rehydrated culture consistently produced CH4 from H2:CO2 and acetate after drying. Drying caused a greater decrease in acetate methanogenic activity compared to H2:CO2 methanogenic activity. Transcript qPCR results for a functional gene in methanogens (mcrA) also revealed significant survivability of rehydrated methanogenic populations. Inactivation due to drying differed among genera, with least to most inactivation in the order Methanospirillum \u3c Methanosaeta \u3c Methanoculleus