Effect of impeller speed and pH on the production of poly(3-hydroxybutyrate) using Bacillus cereus SPV.

P(3HB), is one of the most well studied polyhydroxyalkanoates. It is biodegradable, biocompatible, exhibits thermoplastic properties and can be produced from renewable carbon sources. The commercial exploitation of P(3HB) has been mainly held back by its high production costs. Hence, a lot of research is required to optimize P(3HB) fermentation conditions. In this study we have focused on the effects of impeller speed and pH on P(3HB) production in Bacillus cereus SPV. Four different impeller speeds, 50, 125, 250, and 500 rpm, were used. The highest amount of P(3HB) accumulation was achieved using 125 rpm impeller speed (34% dcw) and this was attributed to optimal cell growth rate. Also, pH-stat fermentations were carried out at pH 3.0, 6.8, and 10. This study confirmed that lack of P(3HB) degradation during unbuffered Bacillus fermentations is due to the low pH conditions. This observation is crucial for the industrial exploitation of the genus Bacillus for the production of P(3HB).