|DIEZ-GONZALEZ, F - CORNELL UNIVERSITY
|HUNTER, J - CORNELL UNIVERSITY
Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/1996
Publication Date: N/A
Interpretive Summary: Acid whey from cheese making is a major source of environmental pollution that has not been easy to remedy. The material is too dilute to ship, too acidic to be used as an animal feed and not valuable enough to dehydrate. One possible mechanism of disposal could be bioconversion. We have identified a bacterium, Clostridium acetobutylicum, that is able to utilize elactate from acid whey. This paper describes the enzymes that C. acetobutylicum uses to ferment lactate. Lactate utilization by C. acetobutylicum may provide a means of converting acid whey into industrial solvents.
Technical Abstract: Clostridium acetobutylicum strain P262 ferments lactate and acetate and produces butyrate. Extracts of cells growing on lactate and acetate had NAD-dependent (nLDH) and NAD-independent lactate dehydrogenase (iLDH) activities. The nLDH was reversible, specific for L(+)-lactate, and activated by fructose-1,6-phosphate (FDP). FDP-dependent, NAD-linked lactate oxidation was only with the purified nLDH, not with cell-free extracts. Cells fermenting glucose had more than 2 mM FDP, but cells fermenting lactate less than 1 uM. The iLDH was FDP-independent, oxidized lactate at a rapid rate, and reduced either MTT or DCPIP but not methyl viologen (MV) or benzyl viologen (BV). C. acetobutylicum P262 had NAD- independent butyryl-CoA dehydrogenase activities, and crotonyl-CoA reduction could be driven by reduced MV but not reduced MTT. Butyryl-CoA oxidation was driven by MTT but not MV. After DEAE-cellulose chromatography, butyryl-CoA dehydrogenase activities were found in two distinct fractions, but instability prevented further purification of eith- er one. NAD-independent B-hydroxybutyryl-CoA dehydrogenase activity could not be detected. Based on the stoichiometry of the fermentation, the iLDH produced more reducing equivalents than the butyryl-CoA dehydrogenase could utilize. This latter result indicated that reducing equivalents might also be passing from the iLDH to NAD-linked B-hydroxybutyryl-CoA dehydrogenase.