Isolation and identification of thermophilic cyanobacterium inhabiting Shiv Kund (Sohna hot spring), India through polyphasic approach: Bioprospecting in varying nitrogen environment for biotechnological interest particularly for biofuel potential

Identifying a potential candidate having optimal growth characteristics and high-value biotechnological attributes, especially biofuel profile in the era of high rising renewable energy demands is necessary for a sustainable algal-biorefinery perspective. Thermophilic cyanobacteria are scarcely investigated for their industrial potential. In this regard, a preliminary study was performed to isolate a thermophilic cyanobacterium from Shiv Kund, Sohna hot spring, Gurugram, India. The polyphasic approach with molecular identification through 16SrRNA and phylogenetic analysis identified the isolated thermophilic cyanobacterium as Fischerella thermalis PCC 7521 based on the 99.15 % similarity in the NCBI-BLASTn results. Further, the phenotypic visualization under light microscopy and Scanning Electron Microscope (SEM) confirms the true-branching filamentous nitrogen fixing cyanobacterium. To examine its potential for a biotechnological perspective, the effect of different nitrogen concentrations in the growth medium on the biochemical profiling was studied. The highest biomass production and biomass productivity per day obtained was 1041.6 mg/L and 42.33 ± 1.52 mg/L/d^⁎⁎(p < 0.01) in 0.1875 g/L (N/8) and 1.5 g/L (N) sodium nitrate concentration respectively. The effect of the growth phase on the biochemical profiling was also prominent and studying optimization helps in the cost-effective production of the required product. Surprisingly, nitrogen starvation has resulted in the increased production of pigments (chlorophyll, phycocyanin and carotenoids), proteins and lipids. The maximum carbohydrate production observed was under complete nitrogen availability (N) in the growth medium with 37.4 % more production in N than complete nitrogen starvation (N₀) on 15th day of the growth cycle. Interestingly, the total lipid production observed was 457.41 ± 18.3 μg/mg ^⁎(p ≤ 0.05) in N₀ condition and 519.28 ± 21.3 μg/mg ^⁎⁎(p < 0.01) in N/8 condition on 15th and 20th day of the growth cycle respectively. The effect of nitrogen concentrations on the C/N ratio and different functional groups were also examined. Overall, the results indicated F. thermalis PCC 7521 is a promising candidate for different biotechnological fields, especially biofuel production.