Optimization and Characterization of Polyhydroxyalkanoates and its Copolymers Synthesized by Isolated Yeasts

Abstract

The present study investigates the role of yeasts, isolated from different environments for its abilities to synthesize biodegradable polymer, Polyhydroxyalkanoates (PHA) and its copolymers. Serial dilution method and spread plate technique had been used for the isolation of yeasts from different samples. Screening had been done by crotonic assay followed by UV Spectrophotometric analysis. Growth parameters such as effect of carbon sources, incubation period, inoculum percentage, incubation temperature and pH of the production medium were optimized for each of the screened isolates. Characterization of PHA was done by FTIR and GC-MS analysis. Maximum PHA produced was observed after 96 hours of incubation period inoculated with 2% (v/v) of inoculum in minimal media of pH 8 containing various carbon sources viz. 5% sucrose for Isolate1; 5% glucose for Isolate 2; 3% starch for Isolate 3 and 5% Lactose for Isolate 4. Incubation temperature was maintained at 37°C. Maximum PHA production was noted as 40 % in Isolate 1, 33% in Isolate 2, 29% in Isolate 3and 25% in Isolate 4 respectively on the basis of dry cell weight under optimized condition. Prominent peaks obtained through FTIR analysis at wavelength 3273, 2922, 1739 and 1462 cm -1 showed the presence of stretching bands of –OH-,-CH-, -C=O- and –CH3- group which are the characteristic peaks of PHA polymer. GC-MS chromatogram detected the peaks at retention time 3.063 and 19.25 min were corresponding to the derivatized products of butanoic acid (polyhydroxybutyrate) and octadecanoic acid (polyhydroxyoctadecanoate).The present study demonstrated that yeast Isolate 1 could produce high amount of PHA (40% on dry cell weight basis ) with hydroxybutyrate (HB) and hydroxyoctadecanoate (HOD) as its main constituents.