Effect of amino acid supplementation on the synthesis of poly(3-hydroxybutyrate) by recombinant pha+Sa Escherichia coli

Abstract

The effect of different amino acid supplements to the basal medium on poly(3-hydroxybutyrate) (PHB) accumulation by recombinant pha Sa + Escherichia coli (ATCC: PTA-1579) harbouring the poly(3-hydroxybutyrate)-synthesizing genes from Streptomyces aureofaciens NRRL 2209 was studied. With the exception of glycine and valine, all other amino acid supplements brought about enhancement of PHB accumulation. In particular, cysteine, isoleucine or methionine supplementation increased PHB accumulation by 60, 45 and 61% respectively by the recombinant E. coli as compared with PHB accumulation by this organism in the basal medium. The effect of co-ordinated addition of assorted combinations of these three amino acids on PHB accumulation was studied using a 23 factorial design. The three-factor interaction analyses revealed that the effect of the three amino acids on PHB accumulation by the recombinant E. coli was in the order of cysteine > methionine > isoleucine. The defined medium supplemented with cysteine, methionine and isoleucine at the concentration of 150 mgl−1 each and glycerol as the carbon source was the optimum medium that resulted in the accumulation of about 52% PHB of cell dry weight.