Determination of the cultivation potential of chlorella vulgaris and stichococcus deasonii isolated from the black sea

In this study, the effects of environmental stress factors on the optimization of culture conditions, biomass and oil yield and biochemical contents of local microalgae strains of Chlorella vulgaris and Stichococcus deasonii isolated from the Black Sea were evaluated. Biochemical analysis results showed that C. vulgaris contained 39.24% protein, 18.98% lipids, and an energy value of 4733 cal/g, while S. deasonii had 34.3% protein, 30.95% lipids, and a caloric content of 5301 cal/g. In terms of fatty acid profiles, both species had higher unsaturated fatty acids compared to saturated ones. In C. vulgaris, the total PUFA ratio was 61.35%, with linolenic acid (30.10%) being the most dominant fatty acid. In S. deasonii, the PUFA ratio was 42.44%, and linolenic acid (30.05%) was again the most dominant. Amino acid analysis detected 16 different amino acids in C. vulgaris and 17 in S. deasonii. In both species, proline, histidine, tyrosine, and glycine were found at the highest levels. In single-variable stress tests: For C. vulgaris in temperature application, the best growth (OD: 1.904), dry weight (0.87 g/L), and maximum lipid content (31.86%) were observed at 23°C. In light intensity application, maximum growth (OD: 2.73) was achieved at 5 klx, maximum dry weight (1.55 g/L) at 10 klx, and maximum lipid content (28.04%) at 20 klx. In salinity application, the best growth (OD: 3.220) and biomass (0.751 g/L) were obtained at 18‰, while maximum lipid content (25.02%) was observed at 22‰. For S. deasonii in temperature tests, the best growth (OD: 1.051) and biomass (0.8 g/L) were recorded at 24°C, while maximum lipid yield (31.4%) was found at 14°C. In light intensity application, the best growth (OD: 2.644) was observed at 10 klux, the highest dry weight (1.070 g/L) at 15 klx, and maximum lipid yield (47.85%) at 10 klx. In salinity tests, the best growth (OD: 3.668) and biomass (2.082 g/L) were recorded at 15‰, while maximum lipid content (33.86%) was observed at 22‰. In optimization analyses conducted using the Response Surface Methodology (Box-Behnken design), it was determined that for C. vulgaris: Dry weight yield was influenced by light intensity (73.4%), temperature (25.1%), and salinity (1.4%). Lipid yield was affected by temperature (80.9%), salinity (11.3%), and light intensity (7.8%). Chlorophyll-a yield was primarily influenced by light intensity (97.7%), salinity (1.8%), and temperature (0.5%). For S. deasoni: Dry weight yield was impacted by light intensity (51.1%), temperature (34.1%), and salinity (14.8%). Lipid yield was mainly affected by salinity (57.4%), temperature (42.5%), and light intensity (0.01%). Chlorophyll-a yield was influenced by temperature (39.3%), light intensity (37.6%), and salinity (23.1%). Experimental studies on biotechnological utilization potential have shown that increasing the inoculation rate reduces the specific growth rate. The minimum doubling time was calculated as 19.21 hours for C. vulgaris and 29.76 hours for S. deasonii. While C. vulgaris supported rotifer (Brachionus sp.) growth (302 rotifers/mL), making it suitable for live feed applications, S. deasonii showed low performance (124 rotifers/mL). The sedimentation rate was recorded as 96.81% for C. vulgaris and 83.44% for S. deasonii. Both microalgae were found to have moderate antimicrobial effects against the bacterium Aeromonas hydrophila. In conclusion, this study presented the first comprehensive culture protocol for Black Sea origin C. vulgaris and S. deasonii and demonstrated the feasibility of using these species in biotechnological applications, especially for their high lipid yields and biochemical contents.