Production of Poly (3-hydroxybutyrate) from cassava starch hydrolysate by Pseudomonas aeruginosa NCIB 950

Abstract

The biosynthesis of polyhydroxybutyrate by Pseudomonas aeruginosa grown on reducing sugar hydrolysate obtained from raw cassava starch as the sole carbon source and di-ammonium sulphate as the limiting nutrient was investigated. This involved hydrolysis of extracted starch from freshly harvested cassava tubers using enzyme-enzyme method of hydrolysis, followed by aerobic fermentation of Pseudomonas aeruginosa on a mixture of the hydrolysate and nutrient media in batch cultures. The biomass growth was measured by cell dry weight and the polyhydroxybutyrate content measured by gas chromatography. The results obtained show that the hydrolysate supported the growth of the organism and when the fermentation was shutdown after 84 h, a biomass yield on substrate (Y x/s ) of 0.186 g g -1 was obtained with corresponding product yield on substrate (Y p/s ) of 0.106 g g -1 . The results also show that the organism accumulated polyhydroxybutyrate in excess of 50 % of the cell dry weight by giving a final polyhydroxybutyrate yield on biomass (Y p/x ) of 0.577 g g -1 which agrees with the general trend in polyhydroxybutyrate production.