Intra-colony light regulates morphology diversity of colonial cyanobacteria

Morphological diversity widely exists in colonial cyanobacteria, which poses a challenge to monitor and predict population dynamics. Light-induced adaptation plays a key role in the underlying mechanisms. Here, to demonstrate how morphological parameters adapt to physiological features (such as pigments and gas vesicles) under light limitation, a model of intra-colony light regimes (ICLR) was developed based on the colonies of Microcystis Kützing. that caused cyanobacterial harmful blooms worldwide. Cell pigments and gas vesicles positively regulated cellular light attenuation coefficient (D(λ)cell), and both accounted for the D(λ)cell variation of 68.2 % and 30.1 %, respectively. According to the ICLR model, D(λ)cell negatively correlated with colony thickness, and a positive relationship existed between colony thickness and cell-to-cell distance (an indicator of colony compactness). Therefore, increasing cell-to-cell distance is an effective strategy when the D(λ)cell is high or colonies are light-limiting, facilitating the formation of loose, large colonies. This pattern was also observed in Microcystis populations in eutrophic Lake Taihu (China) and cyanobacterial Nostoc sphaeroides Kützing, showing cell-to-cell distance positively related to colony thickness or colony depth. This suggests that the predicted morphological adaptation patterns based on the ICLR model are more general in colony-forming cyanobacteria. These findings provide new insights into the morphology diversity of colonial cyanobacteria toward changing environments.