Anaerobic bioconversion of cellulose by Ruminococcus albus, Methanobrevibacter smithii, and Methanosarcina barkeri

A system is described that combines the fermentation of cellulose to acetat e, CH4, and CO2 by Ruminococcus albus and Methanobrevibacter smithii with t he fermentation of acetate to CH4 and CO2 by Methanosarcina barkeri to conv ert cellulose to CH4 and CO2. A cellulose-containing medium was pumped into a co-culture of the cellulolytic R. albus and the H-2-using methanogen, Mb . smithii. The effluent was fed into a holding reservoir, adjusted to pH 4. 5, and then pumped into a culture of Ms. barkeri maintained at constant vol ume by pumping out culture contents. Fermentation of 1% cellulose to CH4 an d CO2 was accomplished during 132 days of operation with retention times (R Ts) of the Ms. barkeri culture of 7.5-3.8 days. Rates of acetate utilizatio n were 9.5-17.3 mmol l(-1) day(-1) and increased with decreasing RT. The K- s for acetate utilization was 6-8 mM. The two-stage system can be used as a model system for studying biological and physical parameters that influenc e the bioconversion process. Our results suggest that manipulating the diff erent phases of cellulose fermentation separately can effectively balance t he pH and ionic requirements of the acid-producing phase with the acid-usin g phase of the overall fermentation.