Production of lipids and formation and mobilization of lipid bodies in Chlorella vulgaris

We investigated the formation of lipid bodies in the microalga Chlorella vulgaris CCALA 256 under lipid-induction conditions in autotrophically grown cultures. We found that cell division ceased after depletion of nitrates from the growth medium within the first days of cultivation. The growth of non-dividing cells subsequently led to the rapid accumulation of lipids. We describe in detail both biogenesis and mobilization of lipid bodies using fluorescence and transmission electron microscopy. Small lipid bodies fused very soon after their creation in the cytosol, forming, eventually, one huge lipid body. In stationary growth phase, lipids were present in the form of a large lipid body occupying most of the cell volume. After replenishment of nitrogen, lipid content decreased rapidly and, within 24 hours, the large lipid body was fragmented into smaller ones. This mobilization of the cellular lipid store occurred independently of light.