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Usage of renewable raw materials for production of fully degradable bioplastics (bacterial poly-3-hydroxybutyrate, PHB) has gained immense research impetus considering recalcitrant nature of petroleum based plastics, dwindling fossil fuel feed stocks, and associated green house gas emissions. However, high production cost of PHB is the major bottleneck for its wide range industrial applications. In current study, Bacillus cereus PS 10, a recent isolate, efficiently utilized molasses, an abundantly available by-product from sugar industries as sole carbon source for growth and PHB production. Most influential bioprocess variables i.e. molasses, pH and NH4Cl were identified based on Plackett-Burman-designed experiments. Design of experiment approach (response surface methodology) was further employed for optimization of these bioprocess variables, and an enhanced PHB yield (57.5%) was obtained. PHB produced by Bacillus cereus PS 10 was investigated using various physico-chemical approaches viz. thermogravimetric analysis, proton and carbon NMR ((1)H and (13)C) spectroscopy, melting point, elemental analysis and polarimetry for its detail characterization, and assessment for industrial application potential., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Poly-β-hydroxybutyrate (PHB) may serve as one of the imperative substitutes for petroleum derived plastics because of their close functional analogy and biodegradation quality. In the present study, PHB producing ability of bacterial isolates was examined on low-cost agro industrial residues. Isolate PS-10 from domestic waste landfills, identified as Bacillus cereus PS-10 produced and accumulated appreciable amount of PHB. Bacillus cereus PS-10 was capable of using a wide variety of agro-based residues viz. maize bran, rice husk, wood waste, molasses, whey etc. as cost-effective carbon sources for PHB production. Molasses at 3% (w/v) supported maximum PHB production (9.5 gl(-1)) and was followed by glycerol (8.9 gl(-1)) at 2% (w/v). Certain carbon sources like almond shell powder and walnut shell powder are being reported for the first time for PHB production and supported reasonable PHB yield i.e. 6.6 and 4.6 gl(-1), respectively. Different cost-effective nitrogen sources like corn steep liquor, chick pea bran, soy bean meal, mustard cake etc. were used for PHB production. Highest PHB production was observed at pH 7 (9.6 gl(-1)) after 48 hrs of fermentation, although B. cereus PS-10 grew and produced PHB over pH range of 5-9. Optimum inoculum level for maximum PHB production was found to be 5% v/v (A600 0.9; approximately 10(8) cfu ml(-1)). Fourier transform infrared spectroscopy (FT-IR) analysis of the extracted PHB showed characteristic peaks (1721.95, 1632.19 and 2926.43 cm(-1)) similar to standard PHB. Melting point of PHB was found to be 185°C. Bacillus cereus PS-10 may be a sound PHB producer, especially by exploiting low cost substrates.

Poly-β-hydroxybutyrate (PHB) has attracted a great deal of attention in recent years due to its potential use for production of fully degradable bioplastics, however, high cost of PHB production is the major bottleneck for its wide range industrial applications. In the current study rice straw hydrolysate (RSH) was employed as a cost-effective substrate for PHB production. RSH was prepared based on biphasic acid-pretreatment of rice straw i.e. first phase treatment with 1% sulphuric acid at 121 °C for 45 min, followed by second phase treatment using 5% sulphuric acid at 121 °C for 60 min (solid:liquid ratio, 1:10). RSH turned out be an efficient substrate for PHB production from a recently isolated Bacillus cereus PS 10, and yielded higher PHB amount than that obtained with glucose (8.6g/L in glucose based medium vs 10.61 g/L in RSH based medium) after response surface methodology (RSM) based optimization. Design of experiments based on RSM was used to optimize three process variables i.e. amount of RSH and NH4Cl, and medium pH, and enhanced PHB yield (23.3%) was obtained. PHB produced was investigated by differential scanning calorimetry and X-ray diffraction powder analysis., (Copyright © 2015 Elsevier B.V. All rights reserved.)