METHANOGENESIS OF GLUCOSE BY DEFINED THERMOPHILIC COCULTURE OF CLOSTRIDIUM-THERMOACETICUM AND METHANOSARCINA SP

Methanogenesis of glucose by defined thermophilic coculture of Clostridium thermoaceticum 1745 and methanosarcina sp. CHTI 55 was carried out to establish a symbiotic culture. In the coculture, glucose was first converted to acetate (inhibitory product) by C. thermoaceticum and the acetate was subsequently reduced to CH4 and CO2 by Methanosarcina sp., suggesting that acetoclastic methanogenesis was the rate limiting step of the system. The inoculum ratio of Methanosarcina sp.(M) to C. thermoaceticum (C), M/C, was a key parameter capable of controlling acetate disappearance during culture, i.e., an M/C of 9.5 resulted in acetate appearance at the beginning of culture, although no acetate accumulation was observed by an M/C of 45.8 yielding 80 mM methane from 40 mM glucose with 4 d culture. The growth kinetics of each monoculture were studied in order to conduct kinetic analysis of the coculture system. The inhibition kinetics of glucose (substrate) and acetate (product) on the growth of C. thermoaceticum were analyzed by a second-order substrate inhibition model coupled with a non-competitive product inhibition model. The analysis revealed that the substrate saturation constant values were K(s) = 80.1 mM glucose; substrate inhibition constant, K(i) = 104.4 mM glucose; and inhibition constant, K(p) = 0.218 mM (undissociated acetic acid); exponent of inhibition, n = 1.04; and mu-m was 0.19h-1. Using a similar second-order substrate inhibition model, the values for Methanosarcine sp. were K(s) = 0.13 mM; k(i) - 0.62 mM (undissociated acetic acid); and the maximum specific rate of CH4 production, q(m) = 17.31 mL CH4/g cell/h.