Molecular Basis of Nitrogen Fixation and the Ecological Success of the Marine Cyanobacterium Trichodesmium

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The ecological success of the blue-green bacterium Trichodesmium species suggests that this cyanobacterium possesses unique characteristics that confer an ecological advantage in the warm, nutrient-poor waters of tropical and subtropical oceans. Furthermore, this filamentous cyanobacterium without heterocysts dominates the free-living nitrogen (N2) fixing cyanobacterium found in the open ocean. It is also the only nonheterocystic cyanobacterium that fixes molecular nitrogen in the light, while evolving oxygen through photosynthesis. Results from previous studies on the molecular biology of Trichodesmium have provided a firm basis for studying its genetic, biochemical, and ecological aspects. This project addresses three important issues of Trichodesmium biology and ecology. First, what is the genetic variability among Trichodesmium populations with different colony morphologies? Second, what mechanisms are involved in its ability to maintain oxygen-sensitive nitrogenase activity while evolving oxygen? And third, is the ecological success of Trichodesmium due to its reduced susceptibility to virus infection that is related to extensive modification of Trichodesmium DNA? These issues will be addressed from biochemical and molecular approaches, using molecular probes and antisera developed earlier for Trichodesmium populations.//