Production and characterization of polyhydroxyalkanoic acid from Bacillus thuringiensis using different carbon substrates

Polyhydroxyalkanoic acids (PHA) are biodegradable microbially synthesised polymers which can act as alternatives to conventional petrochemical based plastics. Bacterial isolates from soil and sewage samples were screened for the ability to accumulate PHA using Sudan Black B dye, and growth conditions of the best PHA accumulating bacterium was optimized. The PHA produced was characterized by FTIR spectroscopy. Eight PHA-producing bacteria were isolated and isolate SBC4 which had the highest percentage accumulation of 30% was genotypically identified as Bacillus thuringiensis and selected for further studies. Glucose and ammonium sulfate supplementation afforded the optimum cultural conditions for cell growth and PHA accumulation yielding 0.33 g/l and 0.40 g/l respectively. B. thuringiensis SBC4 utilized corn bran, corn cob and wheat bran for PHA production, with corn cob yielding the highest PHA content of 21.05%. The optimum pH, temperature and incubation time for PHA productions were 7.0, 37 °C and 48 h. The use of all the optimum conditions in a newly modified medium increased the PHA content, with an overall increase in PHA accumulation from 30% to 44.96% equivalent to an increase of 50% in PHA yield. The presence of major peaks such as CO stretching, CH vibrations, COC stretching confirmed PHA production.