The unparalleled performance of Chlorella ohadii, clearly indicated that we lack essential information on the photosynthetic machinery and what sets the upper growth limits. When grown under optimal laboratory or controlled outdoor conditions, this alga, recently isolated from desert biological sand crusts, one of the harshest environments on earth, exhibits the fastest growth rates ever reported for an alga. Division times shorter than 2 h were recorded, while operating a highly coordinated metabolic switch, supporting growth to higher densities than those achieved if abolished.
Using a tailor-made microfluidics labeling system to supply 13CO2 at steady state, we estimated flux patterns in C. ohadii, Chlamydomonas reinhardtii and other algae and compared them with data from C3 and C4 plants. Our analyses identified distinct flux patterns supporting faster growth in photosynthetic cells, with some of the algae exhibiting faster RuBP regeneration, lower glycolysis and anaplerotic pathways towards the tricarboxylic acid cycle, amino acid synthesis and lipid synthesis than in land plants.
Further, as C. ohadii ability to exhibit this unparalleled growth rate under favorable conditions but withstand the harsh BSC habitat must be imprinted in its genome, we have initiated studies to uncover the unique genome characteristics that enable these capabilities. A larger number of ribosome-encoding genes, increased codon bias and strikingly, high intron abundance, were all consistent with the faster growth of C. ohadii. Some of these characteristics highlight general trends in Chlorophyta and Chlorella spp. evolution, and others open new broad avenues for mechanistic exploration of their relationship with growth.