MALTOSE FERMENTATION TO ACETATE, CO2 AND H2 IN THE ANAEROBIC HYPERTHERMOPHILIC ARCHAEON PYROCOCCUS-FURIOSUS - EVIDENCE FOR THE OPERATION OF A NOVEL SUGAR FERMENTATION PATHWAY

The hyperthermophilic anaerobe Pyrococcus furiosus was grown on maltose as energy and carbon source. During growth 1 mol maltose was fermented to 3-4 mol acetate, 6-7 mol H-2 and 3-4 mol CO2. The presence of the following enzyme activities in cell extracts of maltose-grown P. furiosus indicate that the sugar is degraded to pyruvate and H-2 by a modified "nonphosphorylated" Entner-Doudoroff-pathway (the values given in brackets are specific enzyme activities at 100-degrees-C): Glucose: methyl viologen oxidoreductase (0.03 U/mg); 2-keto-3-deoxy-gluconate aldolase (0.03 U/mg); glyceraldehyde: benzyl viologen oxidoreductase (2.6 U/mg), glycerate kinase (2-phosphoglycerate forming) (0.48 U/mg), enolase (10.4 U/mg), pyruvate kinase (1.4 U/mg). Hexo-kinase, glucose-6-phosphate dehydrogenase, 2-keto-3-deoxy-6-phosphogluconate aldolase and phosphofructo-kinase could not be detected. Further conversion of pyruvate to acetate, CO2 and H-2 involves pyruvate: ferredoxin oxidoreductase (0.4 U/mg; T = 60-degrees-C with Clostridium pasteurianum ferredoxin as electron acceptor), hydrogen: methyl viologen oxidoreductase (3.4 U/mg) and ADP-dependent acetyl-CoA synthetase (1.9 U/mg). Phosphate acetyl transferase and acetate kinase could not be detected. The ADP-dependent acetyl-CoA synthetase catalyzes ATP synthesis via the mechanism of substrate level phosphorylation and apparently constitutes the only ATP conserving site during maltose catabolism in P. furiosus. This novel pathway of maltose fermentation to acetate, CO2 and H-2 in the anaerobic archaeon P. furiosus may represent a phylogenetically ancient pathway of sugar fermentation.