Independent regulation of the lipid and starch synthesis pathways by sulfate metabolites in the green microalga Parachlorella kessleri under sulfur starvation conditions.

Abstract Microalgae accumulate neutral lipids in oil bodies under sulfur-starvation conditions, and determination of the molecular basis of lipid accumulation under sulfur-starvation conditions will enable improvement of the production of biofuel. We analyzed two l -cysteine dependent mutants (Srp1 and Srp2) of the green alga Parachlorella kessleri. The wild-type cells accumulated lipids and developed oil bodies under sulfate-depleted conditions but not under sulfate-replete conditions. Srp1 and Srp2 showed suppressed proliferation and lipid and starch accumulation under sulfate-replete conditions but accumulated only lipids under sulfate-depleted conditions. Although the suppressed cell proliferation of the mutants was partially complemented in medium containing l -cysteine as a sulfur source, that of the wild type was completely complemented, and lipids did not accumulate in the wild type or the mutants. Our results suggest that the accumulation of lipids in P. kessleri under sulfate-depleted conditions results from a shortage of sulfate metabolites, such as l -cysteine, and that sulfate promotes starch accumulation. Highlights • Mutants of the green alga Parachlorella kessleri requires l -cysteine for proliferation. • The mutants exhibit not only lipid but also starch accumulation under sulfate-replete conditions. • A shortage of sulfate metabolites and sulfate promotes lipid accumulation and starch accumulation, respectively. [ABSTRACT FROM AUTHOR]