Aim: Characterization of polyhydroxyalkanoates (PHA) accumulated by halophilic bacteria isolated from solar salterns.
Methods and results: Twenty-six halophilic isolates were obtained from solar salterns of Goa, India. They were screened for accumulation of PHA by Sudan black B, Nile blue A and Nile red stains. Strains H15, H16 and H26 were selected based on their intensity of Nile blue A/Nile red fluorescence. On the basis of phenotypic and genotypic characterization, the three isolates were identified as Bacillus megaterium. Growth kinetics and polymer accumulating capacity of strain H16 were studied in E2 mineral media with 2% glucose with/without NaCl. In the absence of NaCl, strain H16 accumulated PHA to 40·0% (w/w) of cell dry weight (CDW) at 42 h of growth, whereas in presence of 5% w/v NaCl, the culture showed longer lag phase of up to 24 h and accumulated a maximum PHA of 39% (w/w) CDW at 54 h of growth. The infrared spectra of both the polymers exhibited peaks at 1733·9 cm(-1) characteristic of C=O. Scans of (1) H nuclear magnetic resonance (NMR) showed a doublet at 2·5 ppm corresponding to methylene group (-CH(2)), the signal at 5·3 ppm corresponded to methine group (-CH-), and another signal at 1·3 ppm corresponded to the methyl group (-CH(3)). Scans of (13)C NMR showed prominent peaks at 20, 40, 67-68 and 170 ppm, indicating the polymer to be homopolymer of 3-hydroxybutyrates. The polymer is stable up to a temperature of 160°C.
Conclusion: Three moderately halophilic isolates (strain H15, H16 and H26) capable of accumulating PHA were isolated from solar salterns of Ribandar Goa, India, and identified as B. megaterium based on phenotypic and genotypic characterization. Strain H16 accumulated polyhydroxybutyrate in the presence and absence of NaCl up to 40% of its CDW.
Significance and impact of the study: This strain would be better suited for production of PHA at industrial level due to its tolerance to high concentration of NaCl.
© 2013 The Society for Applied Microbiology.