Algae Produce More Biofuel When Starved of Nitrogen, But Why?

by Emil Morhardt

Algae, like all organisms, require nitrogen to produce amino acids, the building blocks of proteins, and necessary for DNA synthesis. When deprived of nitrogen, some species, such as the micro alga Chlamydomonas reinhardtii studied by Valledor et al. (2014), produce more lipids (oil) than normal, presumably as a stored energy source to tide them over until nitrogen again becomes available. These lipids could become the major source of biofuel if their production can be sufficiently ramped up. Valledor et al. wanted a better understanding of what was going on at the molecular level in the nitrogen-deprived algae so that they could eventually modify the species genetically to enhance oil production. They limited nitrogen, and quantified the changes in the cellular mix of protein and metabolic products (the proteome and metabolome), looking at the levels of over 1,200 proteins, 845 of which were recognized as enzymes mediating 157 known cellular metabolic pathways, half of those known for this species. Then they reintroduced nitrogen and followed the process further.

Under nitrogen limitation, there was a decrease in proteins involved in photosynthesis, but even though there was an increase in lipid production, there wasn’t much change in the enzymes responsible for it. Changes in the levels of a good many other cellular molecules were also documented though, including a variety that look as though if their production were increased, lipid production might also increase.Thus, the authors uncovered a number of candidate proteins to genetically manipulate. The pathways are extremely complex, however, and it is clear that the nitrogen starvation leading to increased lipid production very substantially alters many aspects of the cellular metabolism. The next step is probably to increase the production of some of these enzymes and see what happens.

Results like this are the usual story in biology. The more closely one looks, the more complicated things get, and sophisticated tools like the high throughput mass spectrometry used here are necessary to get to the bottom of it. Increasing lipid production through genetic engineering will not likely be easy, but probably would not come about at all without this type of basic research. Until you have a fairly good understanding of a metabolic system, it is extremely hard to effectively manipulate it.

Valledor, L., Furuhashi, T., Wienkoop, S., Weckwerth, W., 2014. System-level network analysis of nitrogen starvation and recovery in Chlamydomonas reinhardtii reveals potential new targets for increased lipid accumulation. Biotechnology for Biofuels 7, 171.

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