Isolation, identification, and optimization of growth conditions for the marine microalgae isolated from the Gulf of Mannar, South-east coast of India

Marine microalgae were isolated from the selected locations from the coastal waters of Gulf of Mannar during December 2019 to February 2021. A total of 16 microalgal species were collected and identified morphologically using a light microscope with image capture system. Of these, five pure isolates of three pennate diatoms viz., Cylindrotheca fusiformis, Amphora sp., and Navicula clavata, and two species of green algae (Nannochloropsis salina and Chlorella sp.) were identified morphologically by field-emission scanning electron microscopy (FE-SEM) and confirmed by PCR amplification sequence analysis of 18S rRNA. The isolates confirmed by PCR were C. fusiformis, Amphora sp., N. clavata, and N. salina whereas Chlorella sp., was confirmed through FE-SEM. Optimization of culture conditions for the identified microalgae was studied with different culture media (Diatom Artificial Medium (DAM), F/2 medium, and Walne’s medium) by various salinities to assess their best growth for commercial application. At 30 ppt salinity, the maximum cell density of C. fusiformis observed in DAM was 7.63 × 106 cells/mL, whereas Amphora sp. and N. clavata showed maximum cell density of 1.20 × 106 and 1.35 × 106 cells/mL, respectively, in F/2 medium. At 35 ppt salinity, maximum cell density of Chlorella sp. was 12.1 × 106 cells/mL in the F/2 medium. Similarly, the maximum growth of 13.7 × 106 cells/mL was obtained at 35 ppt salinity for N. salina in Walne’s medium. As the microalgal strains were isolated at succession stage, they can tolerate a wide range of environmental conditions and could be mass produced in outdoor conditions for industrial applications •A total of five species of marine microalgae were isolated and confirmed.•The optimum salinity and nutrient media were standardized for the isolated strains.•Optimum salinity for all the isolates ranged between 30 to 35 ppt.•Maximum growth was obtained in F/2 media for the three isolates.•Isolated strains could be mass produced following protocol standardized in this study.