Characterization of Polyhydroxybutyrate (PHB) Produced by Novel Bacterium Lysinibacillus sphaericus BBKGBS6 Isolated From Soil

Abstract

The aim of the study was to characterization of polyhydroxybutyrate (PHB) produced by novel bacterium Lysinibacillus sphaericus BBKGBS6 isolated from soil. The present study reports that the strain L. sphaericus BBKGBS6, which was isolated from agricultural soil and is capable of producing PHB. Extraction of PHB was done by solvent extraction method. The results indicated the presence of crotonic acid and confirmed the presence of polyhydroxybutyrate in the sample. The FTIR spectra were observed characteristic absorption bonds for ester and the presence of C=O and C–O were obtained. GCMS results showed the major molecular fragmentation were, 117 m/z (C5H9O3 +), 104 m/z (C4H7O3 +), 74 m/z (C3H6O2 +), 61 m/z (C2H3O2 +), 43 m/z (C2H3O), 59 m/z (C2H3O). 1H and 13C NMR spectra were recorded using purified samples. The molecular weight of PHB (5.64 × 105) was estimated based on viscosity measurement. Films were prepared by the solvent casting method. The structure of crystalline polymers can be determined or refined through best fitting of X-ray powder diffraction profiles. The procedures provide results grossly in agreement with respect to the confirmation of the chain in the powder but differing significantly on a more detailed scale. Such differences represent an additional reason of interest in performing a new structural study. Differential scanning calorimetric experiments was performed using Universal V4.5A TA Instruments, (m.p. 156.61 °C; ΔH = 28.54 J/g) USIC Dharwad. The crystallinity (Xc) of PHB is calculated as per equation given below $${{X}_{c}}\,=\,{D}{{H}_{f}} \times {1}00/{D}{{H}_0} \times {W}$$ . The PHB extracted, PHB Sigma and PHB–TS showed two endothermal peaks in between 140 and 200 °C. The enthalpy of melting (ΔHf) was 28.09 J/g for standard PHB and for extracted one is 56.42 J/g. The glass transition temperature of the sample was 140 °C and amorphous temperature was 176.08 °C. Thermo gravimetric analysis (TGA) is a method of thermal analysis in which changes in physical and chemical properties of materials are measured as a function of increasing temperature (with constant heating rate), or as a function of time (with constant temperature and/or constant mass loss). The decomposition temperature at a 10% level determined by TGA for pure PHB in ScCO2 at 70 °C and 22 MPa was 293.32 °C. Tensile strength of PHB film (28.23 Mpa) was carried out according to ASTMD 882 using universal testing machine (Model Lx 5, LYOD ISNT). Water vapor transmission rate of PHB film (29 g/m2/day) was measured as per ASTM E96-95 and carried out according to the desiccant method. Oxygen transmission rate of PHB film 472.36 (cc/m2/day/atm 65% Rh and 27 °C) was measured as per the method of ASTM D-1434-66.