Abstract
The production of polyhydroxybutyrate (PHB) by Bacillus sp. is most often growth associated and is influenced by various physico-chemical parameters. Imbalanced nutrient conditions were often found to result in sporulation and low PHB production in Bacillus sp. In the present investigation, Bacillus mycoides DFC1 strain isolated from garden soil was studied for PHB production in glucose–peptone broth. The effect of glucose/peptone ratio on biomass yield, PHB production and sporulation was investigated. Central composite rotatable design was used to study the interactive effects of three variables: glucose, peptone and pH on cell growth and PHB production. The optimized medium conditions with the constraint ‘to maximize’ cell growth and PHB content were glucose 17.34 g/l, peptone 7.03 g/l at pH 7.3. A maximum dry cell weight of 4.35 g/l and PHB yield of 3.32 g/l amounting to 76.32 % (w/w) of dry cell weight with negligible sporulation at the end of 72 h resulted in a significant increase (1.83–3.32 g/l or 1.82-fold) in the production of PHB in comparison to the medium used in preliminary studies.
Highlights
Polyhydroxyalkanoates (PHAs) are biodegradable polyesters produced by bacteria which are gaining importance as alternative biopolymers to petroleum-based plastics due to their eco-friendly nature
PHAs containing up to C5 monomers are classified as short chain length PHAs, whereas PHAs containing carbon chain length in the range of C6–C14 and[C14 monomers are classified as medium chain length and long chain length PHAs, respectively (Rehm 2003)
The present data corroborated the interference of PHB production by sporulation in B. mycoides DFC1 due to nutrient limitation in
Summary
Polyhydroxyalkanoates (PHAs) are biodegradable polyesters produced by bacteria which are gaining importance as alternative biopolymers to petroleum-based plastics due to their eco-friendly nature. PHAs as intracellular carbon and energy storage granules in response to growth media containing excess carbon substrate and limited quantities of nitrogen source (Anderson and Dawes 1990). They are readily degraded by the depolymerases present in the environmental microflora resulting in the formation of water and CO2 (Suriyamongkol et al 2007). Several Gram positive and Gram negative bacteria are widely known to produce PHAs, only Gram negative bacteria have been extensively studied Bacteria such as Ralstonia eutropha (Cupriavidis necator), Alcaligenes latus and other methylotrophs accumulate PHA when cell growth is hampered due to the limitation of nitrogen/phosphorous/ magnesium/potassium/oxygen or sulphur in the presence of excess carbon source (Doi 1990). The glycerol stock culture maintained at 4 °C was used for inoculum preparation
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