Microbes and Beneficial Microbes

Thermoanaerobacter strains have been widely investigated for biofuel production from carbohydrates while proteins and

amino acids catabolism have received less attention. Amino acid catabolism is challenging under anaerobic conditions unless

hydrogen is removed. Recent reports have demonstrated that Th ermoanaerobacter strains can degrade branched-chain amino

acids (BCAAs) to a mixture of their corresponding fatty acids (BCFAs) and alcohols (BCOHs) when thiosulfate is present. Th e

aim of the presented work to evaluate the ability of these genera to degrade amino acids and better understand the mechanisms

dictating the observed end productratios. Th e type species of thegenera of Th ermoanaerobacter and Caldanaerobacter, were

investigated in batch culture for each of the proteogenic amino acids with and without the addition of thiosulfate as an electron

acceptor. Some strains in the genus could utilize serine and threonine without the addition of thiosulfate with acetate and

ethanol being the dominate products while BCFA/BCOH ratios from BCAA were highly dependent on species and substrate

when thiosulfate was added. BCAA catabolism resulted mixtures of the corresponding BCOH (0.5-5 mM) and BCFA (3.5-

15.5 mM) with partial substrate utilization being observed in some cases. Altering the liquid-gas phase ratio had an impact

on end product ratios; in the case of C. subterraneus subsp. yonseiensis, increasing the L-G ratio from 1.00 to 5.88, the BCOH

formation increased more than 5-fold (with thiosulfate) and less BCFA were produced.