Photoacclimation during senescence and the control of longevity in microalgae

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Aging is a fundamental part of all life, yet there remains considerable debate as to the causes and mechanisms of why organisms age and the 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. Even more surprising, we can slow down ageing in many organisms in the lab such that they have a longer lifespan. A simple but robust way of doing this by reducing the calorie content of their diet, an approach called caloric restriction. 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 followed inevitably by a death phase. We are proposing to examine the way in which cells protect themselves from too much light as they age. Our goal is to determine how the proteins responsible for absorbing light change their organization to toggle from efficient light absorption to energy dissipation as heat, thereby protecting the cell from damage and extending longevity. We also propose to study the determinants of microalgal longevity in culture and the cellular pathways involved in controlling the response. We will examine the expression of genes to identify gene networks that may provide clues as to how cells meet the challenges of senescence and how altering caloric content of the media may affect survival under these conditions. We also propose to examine the biochemical and physiological differences between individuals in a microalgal population of genetically identical cells to examine additional strategies for long-term survival under stressful conditions. Ultimately, the knowledge on the strategies used to survive stationary phase, control cell density and extend longevity will be useful in the 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.