Dog also amazed by discovery of N2 fixing symbiont

By Kelly

While I may be having a few weeks of epic failure, across the globe there are scientists documenting and publishing their epic success. Not since evolution invented photosynthesis* (or more specifically phytoplankton engulfed cyanobacteria and formed chloroplasts) has there been such a beautiful tale of symbiosis. Last week a report in Science described a newly discovered and unusual symbiotic relationship that occurs in the ocean. And the article, in a similar fashion to the dog pictured above, literally blew my hair back.

There are a number of things that make this discovery noteworthy. First of all I should like to point out that nitrogen fixation is equal in importance to carbon fixation, as both elements are required to form organic matter. Indeed, in vast tracts of the ocean the amount of primary productivity that occurs is set by the amount of available fixed nitrogen, which in turn sets the biological component of CO2 drawn down. But nitrogen fixation is a tricky business as it is very sensitive to oxygen and requires lots of energy. In the terrestrial biosphere you may have heard of rotating legumes through your pasture  to fertilize the soil (for all the farmers out there). Well it is the symbiotic bacteria that live in the nodules of the legume’s roots system that do the job, rather than the legumes themselves. And out there in the ocean, Thompson and co authors have just figured out a similar relationship, between a marine microbe (cyanobacteria) and host phytoplankton.

What is unusual about this cyanobacteria is its drastically reduced metabolic machinery (no photosystem II, RuBisCo or TCA cycle for the microbiologists in the audience). As a consequence, it needs a host who can supply it with the organic carbon required as an energy source, and who better than photosynthetic plankton?! And in return the bacteria can supply a constant supply of fixed nitrogen needed for growth. According to the authors while the host phytoplankton may not be the most important species in terms of rates of carbon fixation, its little symbiont may be a significant contributor to global rates of nitrogen fixation.

And what’s more as Jonathan Zehr, one of the authors and all round guru, points out, “Aside from the importance of nitrogen fixation in marine ecosystems, this is such an interesting symbiosis from an evolutionary perspective, because it can be seen as analogous to an early stage in the endosymbiosis that led to chloroplasts”…or when evolution invented photosynthesis.

I know, amazing isn’t it.

For the full article here, you will need access to Science (and be fluent in genetics unless, like me,  you have no problem not understanding entire paragraphs), or you can read the more easily digested interview with the authors here.

* (you didn’t actually think I believed a person invented photosynthesis, did you?)