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BACKGROUND:Bacteria endogenously residing within the plant tissues have attracted significant attention for production of biopolyester,polyhydroxyalkanoates (PHAs).Bacillus cereus RCL 02 (MCC 3436),a leaf endophyte of oleaginous plant Ricinus communis L.accumulates 81％ poly(3-hydroxybutyrate) [P(3HB)] of its cell dry biomass when grown in mineral salts (MS) medium.METHODS:The copolymer production efficiency of B.cereus RCL 02 was evaluated in valeric acid supplemented MS medium under biphasic cultivation condition.The copolymer so produced has been compared with the P(3HB) isolated from RCL 02 in terms of thermal,mechanical and chemical properties.RESULTS:Valeric acid supplementation as co-substrate in the medium has led to the production of copolymer of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) [P(3HB-co-3HV)] with 14.6 mol％ 3HV.The identity of the polymers has been confirmed by X-ray diffraction (XRD) analysis,Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic studies.Thermogravimetric analysis (TGA) revealed that P(3HB) and P(3HB-co-3HV) films degraded at 278.66℃ and 273.49℃,respectively.The P(3HB-co-3HV) showed lower melting temperature (165.03℃) compared to P (3HB) (170.74℃) according to differential scanning calorimetry (DSC).Incorporation of 3HV monomers decreased the tensile strength (21.52 MPa),tensile modulus (0.93 GPa),storage modulus (E’) (0.99 GPa) and increased ％ elongation at break (12.2％) of the copolyester.However,P(3HB) showed better barrier properties with lower water vapor transmission rate (WVTR) of 0.55 g-mil/100 in2/24 h.CONCLUSION:These findings emphasized exploration of endophytic bacterial strain (RCL 02) to produce biodegradable polyesters which might have significant potential for industrial application.