The analysis of the complete genome of Chlorella microalgae, a promising genus for biofuel production, has been completed by the Laboratoire Information Génomique et Structurale of CNRS. The Laboratory is currently heading an international collaboration involving American and Japanese laboratories, composed of The Joint Genome Institute, Department of Energy, (Walnut Creek, California), the University of Nebraska (Lincoln, Nebraska), the Georgia Institute of Technology (Atlanta, Georgia), the City University of New-York (Brooklyn) and the University of Hiroshima (Japan).

The detailed clarification of the Chlorella genome will help make it possible to further develop its industrial use. This analysis has also brought to light unexpected findings at the fundamental level, including the revealing of numerous genes governing the synthesis of flagellar proteins, which suggests that this species could have a sexual cycle that has gone unnoticed until now.

Additionally, the ability of Chlorella algae to synthesize chitin (one of the main components of the exoskeleton of insects and other arthropods and of the cell wall of some species of fungi), could have been inherited from a virus—itself endowed with chitinase, an enzyme capable of specifically breaking down chitin—having secured exclusive use of its host against other viruses incapable of piercing through its protective shell. This “monopoly” scenario illustrates a new mode of co-evolution between viruses and their hosts.

Chlorella is particularly interesting for the development of second-generation biodiesel thanks to its high lipid content (it typically contains only 30% dry matter). Although several genomes of green algae have already been sequenced (Chlamydomonas, Micromonas and Ostreococcus), Chlorella had not been analyzed until now, despite its economic role as long-established food supplement. The analysis of the Chlorella genome, coordinated by Guillaume Blanc, CNRS researcher, predicts 9,791 protein genes, a total comparable to that of its cousin Micromonas.

The comparative analysis of the different genomes of green algae has made it possible to paint a genetic portrait of their common ancestor, which seems to have already possessed most of the phytohormone biosynthesis pathways necessary to the development and growth of land plants.

This work is published online on The Plant Cell journal’s website.