Growth kinetics of thermophilic Methanosarcina spp. isolated from full-scale biogas plants treating animal manures.

This study determines the growth kinetics of thermophilic strains of Methanosarcina spp. from full-scale thermophilic biogas plants. The complete set of kinetic parameters, including maximum specific growth rate µ(max), half saturation constant K(S), acetate threshold concentration and cell growth yield Y(X/S), were determined for six Methanosarcina strains newly isolated from full-scale reactors and the type strain Methanosarcina thermophila TM-1(T). The kinetic experiments were performed in media supplemented with acetate and activated carbon at the optimum growth temperatures of the individual strains, 50-55 degrees C. The µ(max) values of the isolates were in the range of 0.044-0.064 h(-1), the K(S) ranged from 6.5 to 24.7 mM acetate and the threshold for acetate utilization from 0.11 to 0.40 mM. The cell growth yields of the strains were between 0.78 and 2.97 g dry weight cells mol(-1) acetate. The six isolates exhibited significantly higher µ(max) and had higher affinity to acetate than the type strain M. thermophila TM-1(T). Generally, the affinities of thermophilic Methanosarcina strains tested in this study cover a similar range to those reported in the literature for mesophilic Methanosarcina spp. with acetate as substrate. The strains isolated from plants treating mixtures of animal manures and industrial organic wastes had higher affinity for acetate and lower thresholds than strains isolated from reactors operating solely on manures.