The factors affecting PHB production by Bacillus sp. BA-019 in shake flask culture were the composition of culture medium e.g. minerals and culture conditions (temperature, aeration and pH). Hydrolysed starch was utilized as C-source as well as that of glucose for growth and PHB production by Bacillus sp. BA-019 ; i.e. PHB content were 49.64 and 49.69% wt, respectively. Then hydrolysed starch was selected as C-source due to its low cost. Ammonium sulfate and urea were studied as N-source, it was shown that ammonium sulfate was better assimilated by Bacillus sp. BA-019 for growth and PHB production as compared to that of urea. In the investigation on cultivation conditions, the maximum PHB production at 12 h. and highest spore formation at 24 h. of cultivation were observed in all culture conditions studied. In addition, minerals in culture medium such as Mg, Ca and Mn accounted for PHB production and spore formation. The highest PHB content of Bacillus sp. BA-019 was 56.48% wt and 7x10[superscript 3] CFU/ml. spores was determined in the medium containing 200 mg/l of Mg. Lower PHB production was obtained with increasing or decreasing of Mg, while larger number of spores was produced with higher Mg concentration. Similarly, Ca and Mn concentration at 20 and 0.08 mg/l resulting inthe highest PHB content of 56.42% wt (7.6x10[superscript 3] CFU/ml. of spores) and 56.68% wt (7.1x10[superscript 3] CFU/ml. of spores), respectively. Higher PHB production but less spore formation with increasing of Ca and Mn concentrations were investigated. Temperature was shown affected on PHB production and spore formation ; highest PHB content was 53.42% wt and number of spores was 7x10[superscript 3] CFU/ml. at 30 ํC, which was the larger number compared to that of other culture temperatures. Increasing and decreasing of culture temperatures also showed effect on reducing PHB production by Bacillus sp. BA-019. Similarly, temperature affected spore formation ; less spore formation at higher or lower temperature than 30 ํC. Moreover, PHB production was impacted by aeration ; 50 ml. of culture medium with shaking speed of 200 rpm resulting inthe optimal PHB production with maximum PHB content at 53.81% wt, and number of spores was 7x10[superscript 3] CFU/ml. Aeration also had influence on spore formation i.e. less spore formation was observed in higher aeration condition. The pH of culture medium was another factor relating to PHB production and spore formation; maximum PHB content was shown at pH 7.0 with 54.65% wt and 1.8x10[superscript 4] CFU/ml. spores was found. As pH was differed, PHB production was decreased and spore formation was also less.
