Figure 4.

SesA/B/C Invoke Heterogeneity of C-di-GMP Signaling in a Cyanobacterial Community and Act in Different Layers than Red/Far-Red Light-Responsive Phytochromes

(A) A hypothesis of dynamic cell movements inside a microbial mat. Under natural light conditions, the internal cells in a floc will sense a green light-rich environment and turn off c-di-GMP signaling, favoring the motile-planktonic lifestyle. If the internal c-di-GMP-OFF cells retain positive phototactic motility, they may move and reach the upper region, resulting in the reorganization of the heterogeneous c-di-GMP levels in the floc. This would invoke sequential cellular movements in the cyanobacterial community.

(B) A hypothesis of niche differentiation of photoreceptors. Blue light rapidly attenuates in the top layer of photosynthetic microbial mats (Jorgensen et al., 1987, Ohkubo and Miyashita, 2017). Blue/green cyanobacteriochromes may be a shade detector in an upper layer of microbial mats, where sufficient red light is still available. On the other hand, phytochromes may be effective in a darker deep area, where red light diminishes, and therefore cyanobacteria cannot out-compete other bacterial species.