Chisholm and co-author Qinglu Zeng, a CEE postdoc, performed this research using the bacterium Prochlorococcus and its close relative, Synechococcus, which together produce about a sixth of the oxygen in Earth's atmosphere. Prochlorococcus is about one micron in diameter and can reach densities of up to 100 million per liter of seawater; Synechococcus is only slightly larger and a bit less abundant. The viruses that attack both bacteria, called cyanophages, are even more populous.
The bacterial mechanism in play is called a two-component regulatory system, which refers to the microbe's ability to sense and respond to external environmental conditions. This system prompts the bacteria to produce extra proteins that bind to phosphorus and bring it into the cell. The gene carried by the virus encodes this same protein.
"Both the phage and bacterial host have the genes that produce the phosphorus-binding proteins, and we found they can both be up-regulated by the host's two-component regulatory system," says Zeng. "The positive side of infection for bacteria is that they will obtain more phosphorus binders from the phage and maybe more phosphorus, although the bacteria are dying and the phage is actually using the phosphorus for its own ends."
In 2010, Chisholm and Maureen Coleman, now an assistant professor at the University of Chicago, demonstrated that the populations of Prochlorococcus living in the Atlantic Ocean had adapted to the phosphorus limitations of that environment by developing more genes specifically related to the scavenging of phosphorus. This proved to be the sole difference between those populations and their counterparts liv
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| Contact: Denise Brehm brehm@mit.edu 617-253-8069 Massachusetts Institute of Technology, Department of Civil and Environmental Engineering Source:Eurekalert |