This project will explore the genetic and physiological diversity of the marine cyanobacteria Synechococcus, which are major contributors to primary production in the world's oligotrophic oceans. In addition to its role in the oligotrophic oceans, Synechococcus can also be found in mesotrophic and eutrophic waters. This is in sharp contrast to the members of the closely related genus Prochlorococcus that are restricted to the subtropical open oceans. At present it is not clear if the increased range of Synechococcus reflects a broader physiological tolerance by all the strains of this genus, or the existence of ecotypes that are specifically adapted to higher nutrient and colder temperature conditions. These alternate scenarios have very different implications in terms of how the Synechococcus community may respond to changes in environmental conditions such as global climate change or eutrophication of coastal waters.
In this project, this question is being addressed two ways, by characterizing the physiology of multiple genotypes of Synechococcus, and by determining the seasonal abundances of these genotypes in water samples from around the globe. It has been established that marine Synechococcus consists of a number (seven or more) of genetically distinct lineages. Three of these lineages are specifically associated with a characteristic physiology (motility, chromatic adaptation and lack of phycourobilin), and a fourth consists of a single strain which is incapable of utilizing nitrate as a nitrogen source. However, the physiologies associated with the other three genotypes have not yet been determined. To begin to understand physiological responses of all of the genotypes of Synechococcus to factors that are likely to influence their growth and distributions, in this project, several representative strains of each genetic clade are being grown in a range of light levels, temperatures and nitrogen sources.
Several lines of evidence suggest that additional genetic lineages exist in nature but have not yet been cultivated. To explore this further, the genetic diversity in open ocean Synechococcus populations in the Atlantic and Pacific and coastal populations in Puget Sound, Washington are being examined by terminal Restriction Fragment Length Polymorphism and sequencing analyses of the 16S-23S ribosomal RNA internal transcribed spacer (ITS). Using these sequences and those already determined from Synechococcus isolates, primers will be designed that are specific for each of the genetic clades. These primers will be used in real-time quantitative PCR in a set of monthly samples from the same three environments to quantify the abundance of each genetic type over two annual cycles.
This project will directly involve a graduate student and one or more undergraduate students. Establishing a research program in Puget Sound is providing opportunities for additional undergraduate involvement through the UW School of Oceanography senior field course. In addition, data on Synechococcus distributions and dynamics in Puget Sound will be shared with the Washington State Department of Ecology and incorporated into a Puget Sound food web model. Ultimately, examining the global distribution and population dynamics of Synechococcus in conjunction with experiments measuring the growth of each genotype under a suite of physical conditions will provide insights into the relative importance of ecotypic differentiation and physiological plasticity in determining these distributions.
