Sugar utilization in the hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus strain 7324: starch degradation to acetate and CO2 via amodified Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming)

The hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus str ain 7324, rather than the type strain VC16, was found to grow on starch and sulfate as energy and carbon source. Fermentation products and enzyme acti vities were determined in starch-grown cells and compared to those of cells grown on lactate and sulfate. During exponential growth on starch, 1 mol o f glucose-equivalent was incompletely oxidized with sulfate to approximatel y 2 mol acetate, 2 mol CO2 and 1 mol H,S. Starch-grown cells did not contai n measurable amounts of the deazaflavin factor F-420 (<0.03 nmol/mg protein ) and thus did not show the F-420-specific green-blue fluorescence. In cont rast, lactate (1 mol) was completely oxidized with sulfate to 3 mol CO2 by strain 7324, and lactate-grown cells contained high amounts of F-420 (0.6 n mol/mg protein). In extracts of starch-grown cells, the following enzymes o f a modified Embden-Meyerhof pathway were detected: ADP-dependent hexokinas e (ADP-HK), phosphoglucose isomerase, ADP-dependent 6-phosphofructokinase ( ADP-PFK), fructose-1,6-phosphate aldolase, glyceraldehyde-3-phosphate:ferre doxin oxidoreductase (GAP:FdOR), phosphoglycerate mutase, enolase, and pyru vate kinase (PK). Specific activities of ADP-HK, ADP-PFK, GAP:FdOR, and PK were significantly higher in starch-grown cells than in lactate-grown cells , indicating induction of these enzymes during starch catabolism. Pyruvate conversion to acetate involved pyruvate:ferredoxin oxidoreductase and ADP-f orming acetyl-CoA synthetase. The findings indicate that the archaeal sulfa te reducer A. fulgidus strain 7324 converts starch to acetate via a modifie d Embden-Meyerhof pathway and acetyl-CoA synthetase (ADP-forming). This is the first report of growth of a sulfate reducer on starch, i.e. on a polyme ric sugar.