Process optimization for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) co-polymer production by Nostoc muscorum

This study aims at process optimization for poly(3-hydroxybutyrate-co-3-hydroxyvalarate) [P(3HB-co-3HV)] co-polymer production by Nostoc muscorum with respect to variation in different parameters, viz. carbon concentration, time of incubation and pH using response surface methodology (RSM). Under pre-optimized condition, P(3HB-co-3HV) accumulation in N. muscorum reached up to 28.2% (w/w) of dry cells (dcw) in presence of 0.2% acetate + 0.4% propionate, when incubated for 14 days at pH 8.5. A five-level four-factorial central composite design was employed to find out the interactions of four variables, viz. concentrations of acetate and propionate, pH and days of incubation. Using RSM, a second order polynomial equation was obtained by regression analysis. An optimum co-polymer yield of 31.4% (dcw) was achieved at a reduced level of carbons, i.e. 0.11% acetate and 0.08% propionate at pH 8.1 and an incubation period of 16 days. Thus after optimization, though the product yield was increased only by 11%, acetate and propionate requirements were reduced by 45 and 80%, respectively.