Live long and prosper: Acetate and its effects on longevity in batch culturing of Chlamydomonas reinhardtii

The mass cultivation of algal biomass has several challenges, one of which is the poorly developed concepts of aging in batch-culture systems, that could ultimately affect biomass and bioproduct accumulation. While senescence and longevity are successfully applied to multicellular organisms, how these concepts apply to uni-cellular, photosynthetic eukaryotes is less developed. Chlamydomonas reinhardtii is a green mixotrophic micro-alga that can assimilate exogenous acetate as a carbon source as well as relying on photosynthesis for carbon fixation. We tested the hypothesis that caloric content in the media (acetate content) would influence longevity, as has been shown for animals and yeast. Here we describe the development of a culturing system to make studying senescence and aging more tractable while testing the effects of acetate on longevity. In our experi-ments, acetate had clear effects on biomass accumulation, chlorophyll content, starch accumulation, and cellular respiration. Higher levels of acetate also substantially decreased cell survival, observable in this system within 4-6 days. We also show that the high acetate-induced increase in starch levels was correlated with accelerated senescence and death. In support of this, mutants unable to synthesize starch do not show the same reduction in lifespan as the wildtype in high acetate cultures. Collectively, we hypothesize that the remodeling of metabolic flux under high acetate shortens lifespan, which may be due to the excessive redox state of the chloroplast and reactive oxygen generation that can follow. On the surface, this suggests that the concept of caloric restriction applies to photosynthetic mixotrophs and can influence longevity in batch culture systems.

Automated summary

The mass cultivation of algal biomass faces challenges due to the underdeveloped concept of aging, which can affect biomass and bioproduct accumulation. This study examines the effects of acetate content on the longevity of Chlamydomonas reinhardtii and finds that acetate influences biomass accumulation, chlorophyll content, starch accumulation, and cell survival. High acetate levels are correlated with accelerated senescence and death.