Antenna systems, acclimation and the molecular basis of conditional senescence in Chlamydomonas

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Aging and senescence are a fundamental part of all life, yet there remains considerable debate as to the causes and mechanisms of why organisms age and conditions that control longevity. While aging has been of intense interest in multicellular organisms, the realization that unicellular organisms age, including bacteria, has come to many as a surprise. We are proposing to study the process of aging or "conditional senescence" with a model, microalgal system--Chlamydomonas reinhardtii. As cells grow, they reach a maximum cell density as nutrients become depleted and enter a period of limited growth called stationary phase, followed inevitably by a death phase. There are two primary concepts involved with the growth of cells that we are examining. First, we are investigating the strategies microalgae use to minimize oxidative stress induced by light during stationary phase by measuring changes in photosynthesis. In animals, oxidative stress is a leading hypothesis as a cause of aging and algae would be particularly susceptible to oxidative stress during periods of limited growth. These analyses will also examine senescence triggers and the conditions that affect culture longevity. Second, in batch culture, cells reach a maximum cell density and we will test for the presence of "quorum sensing" molecules that are released to control the number of individuals in culture. Our prediction is that these controls on cell density help to conserve nutrients to allow for acclimation and extend the survival time in stationary. Ultimately, the knowledge on the strategies used to survive stationary phase, control cell density and extend longevity will be useful in the budding microalgal biofuel and bioproduct industry, where large scale production of algae is required. An understanding of the limits to cell growth and survival will ultimately affect approaches for the generation of biomass and increasing yields.