THERMOPHILIC ANAEROBIC DEGRADATION OF CARBOHYDRATES - METABOLIC PROPERTIES OF MICROORGANISMS FROM THE DIFFERENT PHASES

Abstract Organisms that might participate in anaerobic, thermophilic degradation of carbohydrates to methane and CO2 and their metabolic properties are shortly reviewed in this paper. More than 20 thermophilic species of classical, fermentative bacteria and of archaebacterial methane bacteria from thermophilic ecosystems have been described and thermophilic acetogenic butyrate‐ and acetate‐degrading consortia have been enriched. As shown for mesophilic degradation thermophilic sulfate reducers might also serve as potential acetogens for the degradation of organic acids and of ethanol in syntrophy with thermophilic methanogens. However, no experimental data are yet available. Pure cultures of thermophilic ‘fermentative’ bacteria can degrade a variety of different sugars and polysaccharides, irrespective of their origin, which was either sewage sludge, soil or a solfataric environment. The sewage sludge organisms Acetomicrobium flavidum and Acetothermus paucivorans fermented glucose via the EMP‐pathway to 2 acetate, 2 CO2 and 4 H2. This fermentation stoichiometry is unique for pure cultures and was previously observed only in syntrophic associations of mesophiles with methanogens or sulfate reducers. Generally, the spectrum of metabolites of thermophilic fermentative isolates seems to be more restricted than that of mesophiles. All methanogenic strains were isolated from sludge or wastewater digesters except for the two Methanothermus species and the thermophilic Methanococcus species, which were from volcanic ecosystems. The substrate spectrum and the metabolism of the thermophilic methanogens did not differ from that of mesophilic representatives. In summary the scheme of Bryant [1] is also suitable for the description of the carbon flow during anaerobic carbohydrate degradation by thermophiles. The complexity of intermediates was dependent on the efficiency of interspecies H2‐transfer. Copyright © 1990, Wiley Blackwell. All rights reserved