RUI: High throughput culturing and ecophysiological analyses of low light adapted Prochlorococcus ecotypes

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The marine cyanobacterium, Prochlorococcus, is the smallest yet most abundant known phototroph on the planet and contributes significantly to primary production and biogeochemical cycling in the world's open oceans. Since its first description 20 years ago, this organism has become a well-studied marine microbe that is being developed as a model system for cross-scale systems biology. At least 26 isolates have been obtained since 1988, from which two distinct ecotypes were identified based on the relative photophysiological characteristics: high-light (HL) adapted and low-light (LL) adapted. More than 80% of the isolates belong to the HL adapted ecotype, which is composed of at least two distinct phylogenetic clades. The other isolates (6) are considered LL adapted and are spread among several phylogenetic clades, two of which are represented by single cultured isolates. Evidence indicates that the two HL adapted clades likely evolved from differences in temperature optima resulting in distinct horizontal distributions of their populations. What is not clear are the phenotypic and/or ecological underpinnings of the different LL adapted clades and the distributions of these clades in space and time, in large part because there are so few isolates representing each clade. Thus, despite the relatively large number of isolates and data on Prochlorococcus, only half the story, that of the more dominant HL adapted ecotypes, is understood in terms of the phylogenetic relationships and distributions. This project will study the physiological characteristics that contribute to the ecology and evolution of different phylogenetic clades that make up the LL adapted Prochlorococcus ecotype. This characterization will be achieved through high throughput culturing and physiological assessment experiments that utilize multi-well plates for purifying new LL adapted isolates, physiological determinations, and a 96-well sampling system attached to a flow cytometer.Broader Impacts: This project will isolate new, axenic cultures with accompanying ecophysiological and phylogenetic information that could be used by biological oceanographers, biogeochemical modelers, microbiologists and evolutionary biologists for further studies of natural population distributions, physiological mechanisms, genomics, transcriptomics, and proteomics of the world's most abundant phototroph. For instance, the 16S-23S rRNA sequences can be used to redesign or develop new primers for environmental detection of LL adapted Prochlorococcus populations and specific ecotypes, which in turn will enable researchers to begin to understand their ecological role in the deeper euphotic zone. New Prochlorococcus isolates will be made available to other researchers as well as deposited in a larger culture collection such as the Center for the Culture of Marine Phytoplankton. Gene sequences will be deposited in the public database, GenBank, and the results from this study will provide information to choose specific strains for further genome sequence analysis. In addition, this project will also provide research opportunities and financial support for several undergraduates to carry out research projects, a MS student in Biology, and the first University of Maine System Cooperative PhD student in Microbiology at USM.