Candida tropicalis BPU1 produces polyhydroxybutyrate on raw starchy substrates

This study reports the potential of Candida tropicalis BPU1-isolated from the rumen of Malabari goat-in producing polyhydroxybutyrate (PHB) on raw starchy substrates. Initially, commercial soluble starch or naturally available raw starchy substrates (flours of potato, tapioca, or jack seed) was supplemented in a minimal medium to evaluate the efficiency of C. tropicalis BPU1 in producing PHB crystals. Among them, potato flour and commercial starch supported the maximum production of PHB at comparable levels of 0.36 g/g and 0.39 g/g cell dry weight (cdw), respectively. Subsequently, using potato flour as substrate, Box-Behnken design and response surface methodology were employed to statistically optimize the culture parameters, which resulted in the 0.6 fold increase (i.e., 0.59 g/g) in production of PHB over the unoptimized condition (potato flour 0.5%, pH 6.9, 38 degrees C, and 19 h incubation). PHB crystals were characterized by TLC, UV-visible spectrophotometry, FTIR spectroscopy, NMR and TGA, which showed typical spherulite morphology during its growth, and were thermostable up to 240 degrees C. Briefly, this study projects the possibilities of the utilization of cheap and raw starchy agro-products as substrate for the production of PHB at a cheaper rate; and that the eukaryotic unicellular C. tropicalis BPU1 offers much industrial significance.