Submitted to: Archives of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/1999
Publication Date: N/A
Interpretive Summary: Lactate production is a detrimental aspect of ruminal fermentation that causes a decrease in pH, indigestion, decreased food intake and even death of the cattle. Some strains of Butyrivibrio fibrisolvens produce large amounts of lactate in vitro, but the contribution of this species to ruminal lactate production was not known. Our results indicated that lactate-producing strains only produced lactate when acetate was not present. Because the rumen always has a high concentration of acetate, B. fibrisolvens would never produce lactate in the rumen. Strains that produced lactate had a novel method of butyrate production that employed butyryl CoA/acetate CoA transferase, and it appears that this enzyme may be used a tool for classifying B. fibrisolvens isolates.
Technical Abstract: Butyrivibrio fibrisolvens strains D1 and A38 produced little lactate, but stain 49 converted as much as 75% of its glucose to lactate. Strain 49 had 10-fold more lactate dehydrogenase (LDH) activity than strains D1 or A38, and this activity was activated by fructose 1,6-bisphosphate (FBP). The role of FBP in regulating the lactate production of strain 49 was, however, ,contradicted by the observation that very low concentrations (< 0.2 mM) gave maximal activity. The pH optimum of the LDH was 6.25, but continuous cultures did not produce additional lactate when the pH was decreased and acetate was available. The lactate production of strain 49 was clearly acetate-dependent. When strain 49 was supplemented with as little as 5 mM acetate, lactate production decreased dramatically, and most of the glucose was converted to butyrate. Strain 49 did not have butyrate kinase, but it had a butyryl CoA/acetate CoA transferase that converted butyryl CoA directly to butyrate. The transferase had a low affinity for acetate (hig K of 5 mM), and this characteristic explained the acetate stimulation and acetate-dependent shift from lactate to butyrate. Strains D1 and A38 had butyrate kinase but not butyryl CoA/acetate CoA transferase, and it appeared that this difference could explain the lack of acetate stimulation and lactate production. Because relatives of strain 49 (Nor37, PI-7, VV1, OB156) all had the same method of butyrate production, it appeared that butyryl CoA/acetate CoA transferase might be a phylogenetic characteristic. A culture of B835, a strain previously grouped with A38 and D1 based on 16S rRNA, had butyryl CoA/acetate CoA transferase activity, and 16S rRNA sequence similarity with strain 49 but not A38 or D1.