Abstract
An extensive screening program was previously done to isolate a promising bacterial isolate Azomonas macrocytogenes isolate P173 capable of polyhydroxybutyrate (PHB) production. It produced 24% PHB per dry weight after 48 h. In this study, several experiments were designed to optimize the composition of the culture medium and environmental factors for maximizing PHB production by the respective isolate. Results show that 60% aeration, incubation temperature 37°C and an initial pH 7.5 were optimum for PHB production. A modified culture medium for PHB production was designed containing 0.7% glucose and 100 mg/L potassium nitrate as a carbon and nitrogen sources, respectively. Using this modified medium together with optimum environmental conditions, PHB production was increased from 24 to 42% per dry weight after 24 h of incubation rather than 48 h. Acriflavin-induced mutation resulted in one variant (173A2) which produced 47% PHB per dry weight after 24 h of incubation using the same modified culture medium except for glycerol 1.5% as carbon source. Key words: Azomonas macrocytogenes, poly-β-hydroxybutyrate, optimization of microbial bioplastics bioplastic.
Highlights
Polyhydroxyalkanoates are precious gifts of biotechnology to mankind
Different concentration of glucose and glycerol were tested as they produced the largest PHB percenttage per dry weight without decreasing biomass to less than 50% attained with other carbon sources
A. macrocytogenes is ellipsoidal to rod-shaped Gram negative cell that is more than 2 mm in diameter, usually
Summary
Polyhydroxyalkanoates (biopolymers; PHA) are precious gifts of biotechnology to mankind. PHA resembles synthetic polymers in many chemical and physical properties, being biodegradable and produced from renewable source makes it superior to its rival. They have a lot of applications, for example they are preferred candidates for developing controlled/sustained release drug delivery vehicles (Nair and Laurencin, 2007) and can be used in biomedical implants and biofuels (Bonartsev et al, 2007; Zhang et al, 2009). PHB production is more expensive than synthetic polymer production so there is a need to explore its production from locally available and renewable carbon sources such as horticultural, agricultural waste, corn, cassava, etc This would be of economic value considering the gains that would result from PHB application (Steinbüchel et al, 1998). Optimization of other culture conditions such as the appropriate time to harvest polymer, aeration levels and incubation temperature is important to manage
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