selective pressures on picocyanobacterial nitrogen use

A central goal of biology is to understand feedbacks between the environments and the genotypes of organisms. Picocyanobacteria dominating open oceans differ in their abilities to utilize nitrate, nitrite and ammonium. We modeled selective pressures on these nitrogen use abilities in a detailed global ocean, and found that the selective consequences of losing nitrate use abilities were weakest in tropical oligotrophic regions, where non-nitrate using ecotypes of Prochlorococcus are abundant in the real world. These analyses not only help us understand the loss of nitrate use within Prochlorococcus, but introduce an approach for studying evolutionary pressures on marine microbial traits.

Figure caption: Diagrams illustrating our modeling approach. (A) Marine Synechococcus and Prochlorococcus isolates vary in their abilities to grow on NH4, NO2 and NO. These nitrogen use abilities are reflected in the genomes of the isolates, including the presence of genes needed for assimilating NH4 (glnA), NO2 (nirA) and NO3 (narB) (solid dots indicate the presence of a particular). (B) All picophytoplankton in the model initially can use NO3, NO2 and NH4. After three years, three different types of mutations occur, each at the same rate, _. The different types of mutants produced are (i) mutants that cannot use NO3; (ii) mutants that cannot use NO2 or NO3; (iii) null mutants that retain the ability to use NO3, NO2 and NH4.

For more information

  • Bragg, J., S. Dutkiewicz, O. Jahn, M. Follows, S.W. Chisholm: Modeling selective pressures on picocyanobacterial nitrogen use in the global ocean. Submitted to Science.