Bioprospecting Sambhar lake haloalkaliphiles for polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHAs) are considered as great sustainable alternative to synthetic plastics due to their biodegradable and biocompatible nature. Extremophiles sustaining high salinity and alkalinity hold great promise for PHA production. This study explores potential of native haloalkaliphilic bacteria of hypersaline Sambhar Salt Lake, India to discover robust strain(s) which can be utilized for industrial-scale PHA production. Based on the BOX-PCR profiling, 27 molecularly diverse isolates were screened for their PHA synthesis potential. Nile Blue A fluorescence intensity based screening revealed 9 high PHA producing bacterial isolates, which predominately belonged to genus Halomonas as confirmed by 16 S rDNA sequencing. The halotolerance assay showed significant NaCl tolerance (up to 15%) by Halomonas species, which further supported their suitability for unsterile fermentation conditions at industrial-scale. GC-MS/MS analysis confirmed that all the 9 isolates synthesized same monomer type i.e. polyhydroxybutyrate (PHB). Considering the highest PHB production (~ 63% of CDW) 'without statistical optimization', Halomonas songnenensis MJPH6, having halotolerance up to 15% NaCl, was selected as representative strain for detailed structural and thermal characterization of PHB using Fourier-Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). High crystallinity and thermal stability (T_d = 300 °C, T_m = 170.53 °C) of synthesized PHB indicated its industrial potential. To the best of our knowledge, it is the first report showing significantly higher PHB production by H. songnenensis MJPH6 under non-optimized nutritional media conditions. Future research prioritizing optimization of fermentation process parameters can facilitate enhanced PHA production in sustainable manner at industrial scale.