Long-Term Survival of Chlamydomonas Reinhardtii During Conditional Senescence

Chlamydomonas reinhardtii undergoes conditional senescence when grown in batch culture due to nutrient limitation. Here we explored plastid and photo-physiological adaptations in Chlamydomonasreinhardtiiduring a long-term ageing experiment by methodically sampling them over 22 weeks. Following exponential growth, Chlamydomonas entered an extended declining growth phase where cells continued to divide, though at a lower rate. Ultimately this ongoing division was fueled by the recycling of macromolecules, that was obvious in the rapidly declining protein and chlorophyll content in the cell during this phase. This process was sufficient to maintain a high level of cell viability as the culture entered stationary phase. Beyond that, cell viability starts to plummet. During the turnover of macromolecules after exponential growth that saw RuBisCO levels drop, the LHCII antenna was relatively stable. This, along with the upregulation of the light stress-related proteins (LHCSR), contributes to an efficient energy dissipation mechanism to protect the ageing cells from photooxidative stress during the senescence process. Ultimately, viability dropped to about 7%at 22 weeks in a batch culture. We anticipate that this research will help further understand the various acclimation strategies carried out by Chlamydomonas to maximize survival under conditional senescence.