PRODUCTION OF POLY-BETA-HYDROXYBUTYRATE ON LACTIC-ACID BY ALCALIGENES-EUTROPHUS H16 IN A 3-1 BIOREACTOR

Poly-beta-hydroxybutyrate (PHB) was produced by. Alcaligenes eutrophus H16 in a 2-l working volume Biostat(R) MD bioreactor in both batch and fed-batch mode, using lactic acid as the sole carbon source during the production phase. For the batch and 2-stage fed-batch fermentations, the organism was first precultivated on a fructose-based, nutrient-rich medium for 24 h, followed by another 24 h on medium in which fructose was omitted and ammonium sulfate supplied as the nitrogen source. In fed-batch fermentations, the dissolved oxygen level was automatically controlled at about 3 to 4.5%. In hatch fermentation with 20 g l-1 of lactic acid as the carbon source and about 9 g (d.m.) of initial cell concentration in the production phase, the maximum PHB concentration obtained in 25 h was 5.8 g l-1, corresponding to 62% of cell dry matter. In 2-stage fed-batch fermentations with the same initial cell concentration and with a total of 20 g l-1 of lactic acid, the maximum PHB concentration increased to 7.5 g l-1, 81% of the dry biomass. In a 1-stage fed-batch fermentation with both the growth and production phases carried out in the bioreactor, the maximum PHB concentration could be increased to 8.4 g l-1, 70% of dry biomass. In this case the total PHB production time was decreased by about 24 h as compared with the 2-stage batch and fed-batch processes. The polymer accumulation could be conveniently monitored by the consumption of acid as the PHB was synthesized.