Bacteria modulate aging physiology in microalgae via induced vesicle production (Microscopic pictures.zip)

In annually reoccurring patterns, microalgae form blooms that persist and decline thereby contributing massively to global biogeochemical cycles. The decline of blooms is mainly caused by nutrient limitation and goes ahead with the aging of individual algal cells. Nutrient intake can re-initiate proliferation, but the processes involved are poorly understood. By investigating the bloom-forming diatom Coscinodiscus radiatus, we demonstrate how algae recover after nutrient influx. The rejuvenation physiology of the algae is characterized by metabolomic re-organization and the formation of extracellular vesicles. Regulated pathways mediating aging are centered around the methionine cycle in C. radiatus. Vesicles shuttle reactive oxygen species, oxylipins and other harmful metabolites out of the old cells, thereby re-enabling their proliferation. Metabolic processes involved in aging and vesicle production are modulated by bacteria. Using chemical signaling bacteria can trigger vesicle production thereby releasing organic nutrients for their growth and modulating algal growth as well.