Single-cell ionomes of terrestrial cryosphere algae

Algae from the Viridiplantae lineage grow on glaciers and semi-permanent snow patches globally. These algal taxa have adapted to extreme environmental conditions, such as freezing temperatures, high light, and oligotrophic nutrient availability. However, how cryosphere algae balance their cellular nutrients to deal with these conditions is not fully known. To address this knowledge gap, we used single-cell inductively coupled plasma-mass spectrometry to quantify the single-cell ionomes (Phosphorus, Magnesium, Calcium, Copper, Iron, Manganese, and Zinc) of cryosphere chlorophyte algae, Microglena sp., Raphidonema sempervirens, and Deuterostichococcus sp., and compared them to mesophile chlorophyte algae, Acutodesmus obliquus and Chlamydomonas reinhardtii. We validated our results through mass spectrometric analyses of digested cultures. When corrected to average cell biovolume, cryosphere algae had lower Phosphorus, Magnesium, and Calcium, consistent with slow cellular metabolism adapted to cold life. Under Phosphorus-starvation, Raphidonema showed no impact of extracellular Phosphorus loss on its single-cell ionome, however, Microglena had a correlative loss of Phosphorus and Magnesium, and an increase in Copper, indicating Phosphorus mobilisation via polyphosphate hydrolysis. Our results provide a comprehensive insight into the single-cell ionomes of cryosphere and mesophile chlorophyte algae and reveal insights into nutrient homeostasis in algal cells adapted to the cryosphere.