Effect of Environmental Stress on Biomolecules Production and Cell Wall Degradation in Chlorella vulgaris

Cell disruption to extract biomolecules for biofuel production, such as lipid and carbohydrate, is one of the challenging downstream processes from an economic standpoint. Environmental stress, namely salt, nitrogen, and temperature, was explored in this study to investigate their effect on lipid and carbohydrate production and cell wall degradation in Chlorella vulgaris UPSI-JRM01. C. vulgaris was cultivated in blue-green 11 (BG11) media following cultivation in salt concentrations of 0, 5, 10, 20, 40, and 60 g/L; nitrogen concentrations of 0, 250, 500, 750, and 1000 mg/L; and temperatures of 28, 25, 40, and 50 °C. Total lipid and carbohydrate content as a percentage of dry weight was determined. Cell wall degradation was measured by polysaccharides content and cell wall thickness. The highest levels of lipid obtained for each stress factor were 40% at a salt concentration of 5 g/L, 51% at a nitrogen concentration of 250 mg/L, and 51% at a temperature of 35 °C. The highest measured concentrations of carbohydrates were 54% at 10 g/L of salt concentration and 61% in deprived nitrogen condition (0 mg/L). Under fluorescence microscopy, the cell wall thickness of calcofluor white-stained cells revealed that cell wall degradation occurred at a nitrogen concentration of 250 mg/L, where the highest lipid concentration (51%) was detected. Under these conditions, the cell wall thickness was 0.154 µm, which corresponded to the lowest total cell wall polysaccharides measured. This study demonstrates the feasibility of nitrogen stress under conditions of a limited nitrogen supply for inducing cell wall degradation and generating a high lipid content.