Sequential accumulation of starch and lipid induced by sulfur deficiency in Chlorella and Parachlorella species

► Starch and lipid accumulation occurred in 4 Chlorellaceae spp. under sulfur deficient conditions. ► Lipids accumulated subsequent to a reduction in stored starch. ► A change in illumination cycle is sufficient for Chlorella lobophora to induce lipid accumulation. ► Fatty acid compositions were altered in Chlorella lobophora and Parachlorella kessleri by sulfur depletion. The influence of sulfur deficiency on biomass production was analyzed in the four Chlorellaceae species, Chlorella vulgaris, Chlorella sorokiniana, Chlorella lobophora, and Parachlorella kessleri. Culturing under sulfur-deficient conditions promoted transient accumulation of starch followed by a steady increase in lipid storage. Transmission electron microscopy indicated an increase and decrease in starch granules and subsequent enlargement of lipid droplets under sulfur-deficient conditions. Chlorellaceae spp. accumulated 1.5–2.7-fold higher amounts of starch and 1.5–2.4-fold higher amounts of lipid under sulfur-deficient conditions than under sulfur-sufficient conditions. More than 75% of the fatty acids that accumulated in Chlorellaceae spp. under the sulfur-sufficient condition were unsaturated and culturing under sulfur-deficient conditions increased the saturated fatty acid content from 24.3% to 59.7% only in P. kessleri. These results indicate that the sequential accumulation of starch and lipid is a response to the sulfur depletion that commonly occurs in Chlorellaceae spp.