Mutagenesis of Bacillus thuringiensis IAM 12077 for increasing poly (-beta-)hydroxybutyrate (PHB) production

摘要

A gram-positive bacterium that accumulated PHB was isolated from local garden soil in Bangalore. Based on its morphological and physiological properties, and nucleotide sequence (about 1.5 kb) of its 16S rDNA it was identified as Bacillus thuringiensis IAM 12077. In this study the PHB-producing capacity of putative mutant strains of Bacillus thuringiensis IAM 12077 was evaluated. A Bacillus sp. identified as a Bacillus thuringiensis IAM 12077 strain capable of producing 10%-15% dry cell weight (DCW) PHB when grown in nutrient broth for 48 h was subjected to random mutagenesis [physical (UV) and chemical (acridine orange)]. Among the UV-mutants screened, 19 putative mutants produced more PHB than the parental, while 2 strains produced less. Of these mutants, 138 exhibited promising PHB accumulation (24.68%; 1.54-fold) with more PHB production (1.3 g/l; 5.4-fold) than the parental strain. Chemical mutagenesis yielded putative mutants, of which 6 had a decrease, 3 had no change, and 2 had an increase (B3, C2) in PHB production. While the increase in accumulation (19.69%, 1.43-fold and 22.22%, 1.62-fold, respectively, for B3 and C2) was comparable to the increase shown by the UV mutant (B8), the yields did not concomitantly increase (0.43g/l, 1.13-fold and 0.6 g/l, 1.57-fold, respectively).