Effects of calcium ion on the colony formation, growth, and photosynthesis in the edible cyanobacterium Nostoc sphaeroides

Abstract

Calcium ions are crucial for the growth and development of photosynthetic organisms, whereas its eco-physiological significance on the edible cyanobacterium Nostoc sphaeroides remains unclear. The percentage of spherical microcolonies from N. sphaeroides vegetative filaments was up to 88–93% after 18 days at higher Ca2+ levels (0.25, 1, and 4 mM), but only about 51% at lower Ca2+ levels (0.01 and 0.06 mM). When cultured at higher Ca2+ levels, N. sphaeroides specific growth rates based on the chlorophyll a content and absolute growth rates based on the dry weight significantly increased by 13–18% and 23–30%, respectively, compared to those at lower Ca2+ levels. The colonies cultured at higher Ca2+ levels exhibited 13–20% increase in light-limited photosynthetic efficiency, 28–42% increase in the maximum electron transport rate and 57–95% increase in the light-saturated photosynthetic rate relative to those at lower Ca2+ levels. The higher Ca2+-treated colonies were more tolerant to high light than lower Ca2+-treated colonies and more rapid recovery of photoinhibited colonies induced by the subsequent dim light was also observed in higher Ca2+-treated colonies. We further found the photosynthetic recovery of photoinhibited colonies required the influx of apoplastic Ca2+ and the maintenance of photosynthetic activity for desiccated colonies during rehydration was also extracellular Ca2+-dependent. These results indicated that higher levels of Ca2+ promoted colony formation, growth, and photosynthesis of N. sphaeroides, suggesting available calcium ions in natural environment may be an important factor affecting its productivity and distribution.