Life and death of Pseudokirchneriella subcapitata: physiological changes during chronological aging

The green alga Pseudokirchneriella subcapitata is widely used in ecotoxicity assays and has great biotechnological potential as feedstock. This work aims to characterize the physiology of this alga associated with the aging resulting from the incubation of cells for 21 days, in the OECD medium, with continuous agitation and light exposure, in a batch mode. After inoculation, cells grow exponentially during 3 days, and the culture presents a typical green color. In this phase, young algal cells present, predominantly, a lunate morphology with the chloroplast occupying a large part of the cell, maximum photosynthetic activity and pigments concentration, and produce starch as a reserve material. Between the 5th and the 12th days of incubation, cells are in the stationary phase. The culture becomes less green, and the cells stop dividing (>= 99% have one nucleus) and start to age. Old algal cells present chloroplast shrinkage, an abrupt decline of chlorophylls content, and photosynthetic capacity (Fv/Fm and phi(PSII)), accompanied by a degradation of starch and an increase of neutral lipids content. The onset of the death phase occurs after the 12th day and is characterized by the loss of cell membrane integrity of some algae (cell death). The culture stays, progressively, yellow, and the majority of the population (similar to 93%) is composed of live cells, chronologically old, with a significant drop in photosynthetic activity (decay > 75% of Fv/Fm and phi(PSII)) and starch content. The information here achieved can be helpful when exploring the potential of this alga in toxicity studies or in biotechnological applications.

Automated summary

This study characterizes the physiology of the green alga Pseudokirchneriella subcapitata during aging. Young algal cells exhibit high photosynthetic activity and starch content, while aging cells experience chloroplast shrinkage, decline in chlorophylls and photosynthetic capacity, as well as degradation of starch. These findings are important for exploring the potential of Pseudokirchneriella subcapitata in toxicity studies or biotechnological applications.