Insights into protein and amino acid metabolism of Thermoanaerobacter mathranii

Abstract

Few investigations have been carried out into the members of the genus Thermoanerobacter for protein and amino acid metabolism compared to carbohydrates, mostly due to the intense interest in bioethanol and biohydrogen in recent decades. The present study investigates the biotechnological potential of Thermoanaerobacter mathranii (DSM 11426) in terms of its ability to produce high-energy alcohols from amino and fatty acids. End product formation from glucose (in the presence and absence of butyrate) as well as from selected proteins and amino acids were analyzed. T. mathranii did not degrade any of the proteins tested to a large extent but degraded several amino acids, namely serine and the branched-chain amino acids (leucine, isoleucine, valine) when cultivated in the presence of thiosulfate. The main end products from the branched-chain amino acids were a mixture of their corresponding branched-chain fatty acids and alcohols, with the strain producing a concentration of the corresponding branched-chain alcohol between 1.0 and 1.7 mM and 8.2–10.9 mM of the corresponding fatty acid. 13C2-labeled leucine revealed that the strains degraded the amino acid in the presence of thiosulfate, producing 3-methyl-1-butyrate, which was then used as an electron acceptor which led to the accumulation of 3-methyl-1-butanol. The strain is highly ethanologenic, producing more than 1.2 mol of ethanol per mol of glucose degraded. The strain was able to reduce volatile fatty acids during glucose fermentation to their corresponding alcohol, further suggesting this strain may be of greater biotechnological value beyond bioethanol production.