Influence of hydrogenothrophic methane formation on the thermophilic anaerobic degradation of protein and amino acids

Abstract Thermophilic (55°C) protein (peptone) degradation was studied in steady state, laboratory-scale reactors. Peptone was easily hydrolysed to amino acids under methanogenic conditions, and all amino acids were completely degraded to volatile fatty acids, carbon dioxide and ammonium. Under these conditions, amino acids known to be oxidatively deaminated were degraded more slowly than the other amino acids. Inhibition of methanogenesis by 2-bromoethanesulfonic acid led to the accumulation of hydrogen in the gas phase and to the immediate inhibition of both protein hydrolysis and the degradation of amino acids that are preferentially oxidatively deaminated. These effects resulted in lower concentrations of all volatile fatty acids except for butyrate and caproate, which increased in concentration. Interspecies hydrogen transfer appeared to be necessary for the complete degradation of alanine, phenylalanine, methionine, valine, leucine and isoleucine. α-Aminobutyrate also accumulated when methanogenesis was inhibited.