... or the life of a unicellular, diazotrophic cyanobacterium
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The general objective of this project is to characterize the physiology of unicellular diazotrophs in relation to the cell cycle, and to predict changes in this process under the influence of multiple and variable environmental forcing conditions.
We propose to fill an important gap by focusing on the unexplored unicellular diazotrophic cyanobacteria, in a study joining complementary approaches: physiology, molecular biology and modeling. Innovative laboratory experiments performed on an original continuous culture device are performed to bring unique sets of data to be compared to mathematical models.
This project adds a new perspective to the nitrogen cycle by focusing on a relatively new compartment (unicellular diazotrophs) and on a process that has been underestimated so far (nitrogen fixation). Models elaborated in this framework will account for the different N acquisition modes and estimate the N budgets and their related C fluxes. Results are expected to shed some light both on the growth of such organisms and on their role as nitrogen providers for their environment
S. Rabouille
A. Sciandra
P. Claquin
A. Dron
P. Chang
C. watsonii (strain WH8501) belongs to a novel genus of marine unicellular diazotrophic bacteria, and is part of "group B" unicellular cyanobacteria. This cyanobacterium would range between ca 2.5 and 6µm in diameter and occur in tropical and subtropical ocean waters, possibly above 24 degC. It has been isolated from open ocean, oligotrophic waters in the western tropical Atlantic and from the tropical Pacific oceans. According to relatively recent works, this diazotrophic cyanobacterium is capable of contributing significantly to oceanic carbon and nitrogen budgets in the tropical regions of the world's oceans.
A first experiment was run on continuous cultures exposed to a 12:12 light-dark regime and an optimal temperature of 27 degrees C. Such conditions are representative of what the strain experiences in nature, and where growth is expected to be balanced. Nitrogen and carbon metabolism were monitored at high frequency and their dynamics was compared to the cell cycle. A daily cycle in the physiological and biochemical parameters could be observed, tightly constrained by the timely decoupled processes of N2 fixation and carbon acquisition.
Dron A., Rabouille S., Claquin P., Le Roy B., Talec A. and Sciandra A. (2011). Light-Dark (12:12) cycle of carbon and nitrogen metabolism in Crocosphaera watsonii WH8501: relation to the cell cycle. DOI: 10.1111/j.1462-2920.2011.02675.x