The metabolism of pyruvate by Lactobacillus plantarum

Abstract

L. plantarum converted pyruvate quantitatively into levorotatory acetoin and CO2 at pH 4. At pH 6 pyruvate decomposition was slower and the amt. of pyruvate was greater than the sum of acetoin, CO2, iactic and acetic acids formed. The initial rate of CO2 formation from pyruvate gradually fell, especially when the pH was below 4. Addition of glucose in catalytic amts. raised the QCO2 and delayed its fall. K phosphate further increased the QCO2 and delayed its fall in the presence of glucose but not in its absence. At high concns. of pyruvate (0.1 [image]), CO2 formation was strongly inhibited. Preliminary incubation of cells at pH 3.8 in buffer solns. without substrate reduced the capacity of the cells to decompose pyruvate. At pH values above 4 the capacity could be restored by glucose. The decomposition of pyruvate by L. plantarum at pH 4 is inhibited by low concns. of fumarate. At all concns. of fumarate, the degree of inhibition of acetoin and CO2 formation is approx. the same. The degree of inhibition by a given concn. of fumarate is greater when glucose is present than when it is not. The formation of CO2 and acetoin from pyruvate by strains of Aerobacter aerogenes and Staphylococcus aureus is also inhibited by fumarate, but with these organisms a higher concn. of fumarate is required. The formation of CO2 and acetoin by L. plantarum is inhibited to a lesser degree by phthalate, succinate, DL-malate, maleate, malonate, barbiturate, cis- and transaconitate and DL-aspartate. The concn. of pantothenate in the suspension medium did not affect the rate of pyruvate decomposition. Cells grown in a medium deficient in thiamine formed very little CO2 or acetoin unless both thiamine and glucose were added to the suspension.