Microbial PHA biosynthesis and its biomedical applications

Polyhydroxyalkanoates (PHAs), are polyesters of 3-, 4- 5- and 6-hydroxyalkanoic acids, produced by a variety of bacterial species under nutrient-limiting conditions with excess carbon[1]. PHA production by Bacillus cereus SPV and Pseudomonas sp. has been explored under different nutrient limiting conditions[2]. Bacillus cereus SPV has been found to produce maximum PHA under nitrogen limiting conditions. Interestingly P(3HB-co-3HV) production was obtained using glucose under potassium-limiting conditions[2]. The Pseudomonas sp. have also been found to utilise a range of different carbon sources including structurally related fatty acids and structurally unrelated carbohydrates. Mcl-PHAs produced include P(3HO), P3(HHX-co-HO-co-HD) and the previously unknown novel mcl-PHA, P(3HO-co-2HDD). The PHAs produced have been used for the production of tissue engineering scaffolds and drug delivery structures with and without Bioglass®[3]. The microstructure, bioactivity and drug release kinetics have been studied. PHA composites with micro-sized bioactive glass (m-BG) have been compared to composites with nano-sized bioactive glass (n-BG)[4]. The incorporation of n-BG particles had a significant reinforcing effect on the composite due to enhancement of the elastic modulus as a function of the n-BG content