EFFECT OF PH ON ORGANIC-ACID PRODUCTION BY CLOSTRIDIUM-PROPIONICUM IN TEST TUBE AND FERMENTER CULTURES

Clostridium propionicum is a chemical autotroph that metabolizes alanine to propionic acid (reduction product) and acetic acid (oxidation product). The ratioof propionate/acetate predicted by the electron balance is 2:1. This study reports the effect of pH on growth and organic acid production by this organism when grown in both test tube cultures initially buffered from pH 7.0 to 5.0, and in fermentors maintained at pH 7.0 and 6.5. Highest growth and organic acid production was found at pH 7.0 in both cases. HPLC analysis showed that at pH 7.0, the ratios of propionate to acetate were 0.45:1 (stationary tube, 24 h). The highest ratio observed was 1.8:1 (stationary tube, pH 6.0, 24 h). This tube produced 8.5% of the acids produced in the pH 7.0 culture tube. The identify of the major portion of the reduction products of the organism remains unknown.