Effect of carbon/nitrogen ratio on polyhydroxyalkanoates production by Bacillus species under submerged fermentation

Aim: To analyze the effect of carbon/nitrogen (C/N) ratio on polyhydroxyalkanoates (PHAs) production by Bacillus species under submerged fermentation process.Methodology: Preserved polyhydroxyalkanoates producing Bacillus sp. C1 (2013) (KF626477) was revived and growth parameters were optimized by one factor at a time approach. The effect of C/N ratio and the influence of time period on polyhydroxyalkanoates production through submerged fermentation process was evaluated under optimized condition. Primary structural and morphological characterization of extracted polyhydroxyalkanoates was carried out by Fourier Transform Infra-Red Spectroscopy and Field Emission-Scanning Electron Microscopy. Results: Bacillus sp. C1 (2013) produced higher cell biomass in mineral salt medium at pH 9.0, temperature 37oC, dextrose (2%) and ammonium sulphate (1%) as carbon and nitrogen source with 15% inoculum size. Under optimized condition, higher polyhydroxyalkanoates production of 1.09 g l-1 (49.2%) was obtained at 48 hrs with 2: 0.4 C/N ratio. However, in our previous study 0.909 gl-1 of PHAs was produced by the bacteria at 6:1 carbon to nitrogen ratio. Fourier Transform Infra-Red Spectroscopic analysis showed high intense absorption bands at 1720.18 cm−1 resembled to ester carbonyl functional group of PHB, which is the most common homopolymer of PHAs. Surface morphology of poly-beta-hydroxybutyrate film was rough and fairly regular as revealed from Field Emission-Scanning Electron Microscopic imaging. Interpretation: Poly-beta-hydroxybutyrate production by the bacteria increased under higher degrees of nitrogen deficient condition. Thus, optimized C/N ratio can improve the cost affordability of poly-beta-hydroxybutyrate production, however, further research in contrast to different bacteria is highly essential in this regard.