Resource utilization by phytoplankton: is nitrogen allocation amongst functional catalysts optimized in response to resource limitation?

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We have entered an era in biological oceanographic research when the information within the genomes of an increasing number of marine organisms is becoming increasingly available. One of the challenges facing biological oceanographers is to exploit this information to obtain greater insight into the functioning of marine ecosystems. Recently, Raleigh Hood and coworkers have posed the questions: o 'What role do all these new genes and proteins (identified by genomic approaches) play in driving marine ecosystem dynamics and biogeochemical cycles? o Which are important and which are not? o What role are they likely to play in the evolution of marine microbial communities, how might they have influenced global biogeochemical cycles over Earth's history, and how might they do so in the future.' (Oceanography, Vol 20, No 2 page 155) These are very challenging questions. We propose to take a small but important step in addressing a subset of issues raised by these questions. Our focus is on one representative of the marine phytoplankton, namely the marine coccolithophore Emiliania huxleyi. Emiliania is one of the thousands of phytoplankton species that contribute to photosynthesis in the sea. As a photosynthetic organism, she sits at the base of the food web that leads to fish and top predators including marine mammals and man. Emiliania is particularly useful to us in the genomic age of oceanographic research because she is one of the few phytoplankton species for which the entire genome is currently available. (http://www.ncbi.nlm.nih.gov/sites/entrez?Db=genomeprj&cmd=ShowDetailView&TermToSearch=9504). The genome sets the limits on the capability of an organism to exploit its environment. However, the genome represents an organism's potential rather than what is actually achieved in a given situation. How an organism exploits the environment becomes manifest in the composition of its proteome. The proteome consists of all of the proteins that are manufactured by a cell. The proteome is not a static entity. Rather, the proteome is a dynamic entity that is reorganized in response to changes in the environment. Of particular interest are changes in the proteome that increase the ability of an organism to obtain resources from the environment and use these resources for growth and reproduction. Also of importance, are changes in the proteome that protect an organism from environmental stress. Growth is promoted when resources are plentiful. These resources include light and inorganic nutrients. Growth is limited when these resources become scare, or when environmental conditions deteriorate. In particular, light is an important limiting factor on seasonal time scales (low-light in winter versus high-light in summer) and with increasing depth in the sea. Nitrogen is the main limiting factor for phytoplankton growth in over 50% of the surface of the sea in summer, with phosphorus an important secondary limiting factor in many regions. Advances in technology now allow both qualitative and quantitative measurements of how the proteome changes in response to environmental factors. Documenting changes in the proteome provides a way to assess how the state of a cell such as Emiliania changes. Our goal is to document changes in the abundance of proteins associated with different bioenergetic and biochemical pathways or functions. This will allow us to assess the cost of acclimation in terms of changes in the proportions of cell biomass amongst these pathways/functions. The goal of our research is to employ this new information to inform a cost-benefit analysis of acclimation within Emiliania huxleyi. Ultimately, this information will contribute to our understanding of adaptation of marine phytoplankton to the range of environmental conditions encountered in the sea.