Growth of Pseudomonas fluorescens on Cassava Starch hydrolysate for Polyhydroxybutyrate production

Abstract

The potential of local strains of microorganism (Pseudomonas fluorescens) in polyhydroxbutyrate production was investigated in this study. This was with a view to establishing the capabilities of local strains of microorganisms on utilizing renewable and locally available substrates in polyhydroxybutyrate production. This involved hydrolysis of starch extracted from freshly harvested cassava tubers using enzyme-enzyme method of hydrolysis, followed by aerobic fermentation of Pseudomonas fluorescens on a mixture of the hydrolysate and nutrient media in a fermentor in batch cultures. The reducing sugar hydrolysate served as the carbon source and diammonium sulphate as the limiting nutrient. The reaction temperature, pH and agitation rate in the fermentor were maintained at 30°C, 7.5 and 400 rpm respectively. The biomass growth was measured by cell dry weight and the polyhydroxybutyrate content measured by gas chromatography. When the fermentation process was shut down after 84 hour, the substrate consumption by the organism was 9.2 g/L to give a dry cell weight of 1.75 g/L resulting in a biomass yield on substrate (Y_x/s) of 0.1902 g/g (19.02 % wt/wt). The gas chromatographic analysis gave a final polyhydroxybutyrate value of 1.254 g/L with corresponding product yield on biomass (Y_p/x) of 0.7166 g g^-1 [71.66% wt/wt] and product yield on substrate (Y_p/s) of 0.1363 g g^-1 [13.63% wt/wt]. The results 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 0.7166 g g^-1 [71.66% wt/wt] which agrees with the general trend in polyhydroxybutyrate production. @ JASEM

J. Appl. Sci. Environ. Manage. December, 2010, Vol. 14 (4) 61 - 66