Biosynthesis of PHB tercopolymer by Bacillus cereus UW85.

Abstract

The study was attempted to determine the ability of a Gram-positive Bacillus cereus UW85 strain to biosynthesize poly (3-hydroxybutyrate) copolymers when epsilon-caprolactone, or epsilon-caprolactone and glucose, were used as carbon sources. Bacillus cereus was grown for 24 h under nitrogen-limited conditions in a mineral salts medium. Growth was monitored by measurement of turbidity. Glucose level was determined by the colorimetric anthrone The epsilon-caprolactone concentration was determined by gas chromatography. The bacterial biopolymers were extracted with chloroform in a Soxhlet extractor and then characterized by nuclear magnetic resonance and gel permeation chromatography. When epsilon-caprolactone was used as a carbon substrate, the bacterial strain produced tercopolymer with 3-hydroxybutyrate, 3-hydroxyvalerate and 6-hydroxyhexanoate units. However, when caprolactone and glucose were supplied together, only homopolymer of poly (3-hydroxybutyrate) was produced. All tercopolymers isolated from B. cereus UW85 cells were obtained with yields up to 9% (w/w) and low number-average molecular weight compared with the homopolymer PHB. Bacillus cereus UW85 produced tercopolymer with a low molecular weight from one substrate (epsilon-caprolactone) used as a carbon source. The results are significant for the potential future application of Bacillus biopolymers to bioplastics production.