PRODUCTION OF POLY(3-HYDROXYBUTYRIC-CO-3-HYDROXYVALERIC)ACID USING PROPIONIC-ACID BY PH REGULATION

Propionic acid has been used as a cosubstrate for the production of th e biodegradable polymer, poly(3-hydroxybutyric-co-3-hydroxyvaleric)aci d, by Alcaligenes eutrophus. Propionic acid is, however, known to inhi bit growth of A. eutrophus at concentrations above 0.5 g/l in the ferm entation broth. In this study, the inhibition of the cell growth due t o the presence of propionic acid was overcome by regulation of the pH. In the case of an initial pH of 7.5, A. eutrophus NCIMB 11599 continu ed to grow up to a propionic acid concentration of 5 g/l, whereas no g rowth occurred in case of an initial pH of 6.5 in a wide concentration range of propionic acid. This enhanced uptake of propionic acid with pH changes seems to be due to a decrease in the concentration of undis sociated propionic acid as an uncoupler. Continuous cultures were perf ormed in a static pH mode. When the pH was maintained at 7.5 during th e fermentation, the dry cell weight was 50% higher than that when the pH was maintained at 6.8.