On the surface of our oceans a phage (i.e. a virus that infects bacteria) risks modifying the fine balance that regulates oxygen and carbon dioxide production. Researchers are focusing their attention, in particular, on Prochlorococcus marinus bacteria, which form a part of plankton and are found mainly in the tropics and subtropics (in staggering numbers: there are approximately 1027, i.e. an octillion, of them), where they make use of sunlight to generate oxygen and, at the same time, store an enormous quantity of carbon dioxide (estimated to be at least 4 billion tonnes). In doing so, they reduce the greenhouse effect.
According to the researchers, these bacteria are the most abundant photosynthetic organisms on earth (i.e. organisms capable of producing oxygen thanks to light and special pigments). They belong to the family of cyanobacteria: the microorganisms that, 2.4 billion years ago, were the first to emit large quantities of oxygen into the atmosphere. Now, however, as we have said, Prochlorococcus marinus bacteria are being attacked by a particular phage, which infects them, robbing them of the energy they produce and reprogramming their genetic code. A team of researchers from Rice University (USA) has attempted to understand how these changes occur and they discovered that phages cause a series of changes in ferredoxin proteins: “When the virus infects the Prochlorococcus marinus”, explained Ian Campbell, main author of the research, “it shuts down production of the bacterial proteins and replaces it with its own variants. I compare it to putting a different operating system on a computer.” In other words, the phages rewire the metabolism of the bacteria, making them produce different ferredoxins than usual, which are used exclusively for the survival of the phage itself. The cyanobacteria do not die, which is what happens when they are infected by other phages, but continue to live, remaining completely subservient to the needs of the virus. And this inhibits the ability of the Prochlorococcus marinus to store CO2 (carbon dioxide).
The results of the study conducted by Rice University were published in the Journal of Biological Chemistry. To create a detailed reconstruction of these mechanisms, the researchers used a sophisticated synthetic biology system, to use the technical term (synthetic biology makes it possible to assemble different “pieces” of the genetic code in order to obtain the desired model). In the case of Prochlorococcus marinus, the researchers reconstructed the active parts of the cyanobacteria and those of the phage inside another bacteria that was much easier to handle and study – Escherichia coli. Research similar to that being conducted by Rice University (which was partially funded by NASA and the US Energy Department) will make it possible to get a clearer picture of the mechanisms used by phages to make the work of cyanobacteria less efficient, and this in turn will help to find a possible solution to avoid what could become a serious ecological problem in the future.