Rhizobium meliloti produced a copolymer of short chain length polyhydroxyalkanoate (scl-PHA) on sucrose and rice bran oil as carbon substrates. Recombinant Escherichia coli (JC7623ABC1J4), bearing PHA synthesis genes, was used to synthesize short chain length-co-medium chain length PHA (scl-co-mcl-PHA) on glucose and decanoic acid. Fourier transform infrared spectroscopy (FTIR) spectra of the PHAs indicated strong characteristic bands at 1282, 1723, and 2934 cm -1 for scl-PHA and at 2933 and 2976 cm -1 for scl-co-mcl-PHA polymer. Differentiation of polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-hydroxyvalerate-P(HB-co-HV) copolymer was obseverd using FTIR, with absorption bands at 1723 and 1281 for PHB, and at 1738, 1134, 1215 cm -1 for HV-copolymer. The copolymers were analyzed by GC and 1 H NMR spectroscopy. Films of polymer blends of PHA produced by R. meliloti and recombinant E. coli were prepared using glycerol, polyethylene glycol, polyvinyl acetate, individually (1:1 ratio), to modify the mechanical properties of the fi lms and these fi lms were evaluated by FTIR and scanning electron microscopy.

Polyhydroxyalkanoate (PHA), which is produced by several bacteria, is a biodegradable polymer that has many industrial and medical applications. This study deals with development of a simple kinetic model and modification of the logistic equation that can provide an adequate description of PHA formation process by Bacillus flexus. The parameters studied were kinetics of microbial growth, substrate consumption, and product formation. The microbial growth was described by simplification of Monod's model. A simplified Luedeking-Piret type model could be employed to represent the product kinetics. The kinetic constants were evaluated on the basis of non-linear regression and the differential equations were solved using Runge-Kutta algorithm and MATLAB software. A good agreement was found between the experimental and predicted values, which indicated that the model differential equations could describe the PHA formation and fermentation process. In this study, a modification of the logistic equation has also been attempted for describing the growth of B. flexus.

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Aims:  The objective of the present work was to utilize an unrefined natural substrate namely mahua (Madhuca sp.) flowers, as a carbon source for the production of bacterial polyhydroxyalkanoate (PHA) copolymer by Bacillus sp‐256. Methods and Results:  In the present work, three bacterial strains were tested for PHA production on mahua flower extract (to impart 20 g l−1 sugar) amongst which, Bacillus sp‐256 produced higher concentration of PHA in its biomass (51%) compared with Rhizobium meliloti (31%) or Sphingomonas sp (22%). Biosynthesis of poly(hydroxybutyrate‐co‐hydroxyvalerate) – P(HB‐co‐HV) – of 90 : 10 mol% by Bacillus sp‐256 was observed by gas chromatographic analysis of the polymer. Major component of the flower is sugars (57% on dry weight basis) and additionally it also contains proteins, vitamins, organic acids and essential oils. The bacterium utilized malic acid present in the substrate as a co‐carbon source for the copolymer production. The flowers could be used in the form of aqueous extract or as whole flowers. PHA content of biomass (%) and yield (g l−1) in a 3·0‐l stirred tank fermentor after 30 h of fermentation under constant pH (7) and dissolved oxygen content (40%) were 54% and 2·7 g l−1, respectively. Corresponding yields for control fermentation with sucrose as carbon source were 52% and 2·5 g l−1. The polymer was characterized by proton NMR. Conclusions:  Utilization of mahua flowers, a natural substrate for bacterial fermentation aimed at PHA production, had additional advantage, as the sugars and organic acids present in the flowers were metabolized by Bacillus sp‐256 to synthesize P(HB‐co‐HV) copolymer. Significance and Impact of the Study:  Literature reports on utilization of suitable cheaper natural substrate for PHA copolymer production is scanty. Mahua flowers used in the present experiment is a cheaper carbon substrate compared with several commercial substrates and it is rich in main carbon as well as co‐carbon sources that can be utilized by bacteria for PHA copolymer production.

Abstractwas isolated from local soil nutrient medium (IM) containing sucrose as carbon source, yield of biomass and polyhydroxyalkanoate (PHA) were 2 g/l and 1 g/l (50% of biomass), respectively. Substitution of inorganic nitrogen by peptone, yeast extract or beef extract resulted in biomass yields of 4.1, 3.9 and 1.6 g/l, respectively. Corresponding yields of PHA in biomass was 30%, 40% and 44%. Cells subjected to change in nutrient condition from organic to inorganic, lacked diaminopimelic acid in the cell wall and the concentration of amino acids also decreased. Under these conditions the extractability of the polymer from the cells by hot chloroform or mild alkali hydrolysis was 86-100% compared to those grown in yeast extract or peptone (32-56%). The results demonstrated that growth, PHA production and the composition of cell wall of present in the growth medium. Cells grown in inorganic medium lysed easily and this can be further exploited for easier recovery of the intracellular PHA.

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