Biosynthesis of polyhydroxyalkanoic acids by Streptomyces coelicolor

Polyhydroxyalkanoates (PHAs) are common carbon and energy storage materials produced by numerous bacterial species when grown in the presence of excess carbon and at least one limiting nutrient essential for growth. PHAs are currently undergoing intensive investigation because of their potential use as biodegradable thermoplastics. PHA synthases are the key enzymes of PHA biosynthesis and catalyse the conversion of 3-hydroxyacyl-CoA substrates to PHAs with the concomitant release of CoA. More than 54 different PHA synthase genes have been cloned and characterised. Multiple alignments of the primary structures of these PHA synthases showed an overall identity of 9-96% with only eight strictly conserved amino acid residues. Streptomyces coelicolor A3(2) M145 (whose entire genome has been sequenced) is a wealthy source of antibiotics. However, PHA production in Streptomyces has yet to be studied in detail. In this work, the polymer from S. coelicolor A3(2) M145, grown in SMM medium, has been isolated and characterised using Nile blue A staining, UV spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR), Gas chromatography and GC-MS. Characterization of the polymer using GC and GC-MS reconfirmed the production of PHB by S. coelicolor A3(2) M145. Further, S. coelicolor A3(2) M145 when grown in Kannan and Rehacek medium was found to produce other polyhydroxyalkanoates such as poly-4-hydroxyvalerate. This was confirmed using GC-MS analysis of the polymer. A correlation study has also been carried out between PHB accumulation and antibiotic production by S. coelicolor A3 (2) M145 which produces mainly three kinds of antibiotics, actinorhodin, gamma actinorhodin, and undecylprodigiosin. This study indicates a possible correlation between the decrease in PHB concentration in the cell and a simultaneous increase in the concentration of actinorhodin, g-actinorhodin and later, undecylprodigiosin. Thus PHB could be one of the possible sources of carbon utilised for antibiotic production. However, further experiments are required to confirm this correlation. Finally, using the recently published putative PHA synthase sequence from S. aureofaciens NRRL 2209 (4), a homologous region has been located in the chromosome of S. coelicolor A3(2) M145. Molecular work is currently underway to probe into the possible role of this fragment in PHA biosynthesis