Green and blue light-dependent morphogenesis, decoupling of phycobilisomes and higher accumulation of reactive oxygen species and lipid contents in Synechococcus elongatus PCC 7942

Cyanobacteria are one of the emerging model systems for the sequestration of CO2 and sustainable production of bioenergy and chemicals. However, the spectral composition of light, which changes greatly in a dynamic light environment, could affect their fitness, growth and development. We studied the photobiology of the model cyanobacterium Synechococcus elongatus PCC 7942 using different lights such as white light (WL), red light (RL), green light (GL) and blue light (BL) to investigate the response of the organism to different wavelengths of photosynthetic active radiation. Results obtained suggested that S. elongatus PCC 7942 can not efficiently utilize green and blue wavelengths of light, and the two light colors compromised the fitness and growth of the or-ganism by inducing high levels of reactive oxygen species (ROS). GL and BL, interestingly, increased the lipid content in the biomass and caused decoupling of phycobilisomes from the thylakoid membranes. We report light quality-dependent morphogenesis in S. elongatus PCC 7942 where GL and BL caused cell elongation while RL induced small cell morphology. Gene expression analysis suggested that GL and BL could regulate cell shape by altering the expression of cytoskeleton protein-encoding morphogenes. Thus, it is evident that the growth and fitness of S. elongatus PCC 7942 can be compromised in dense culture or at higher depths in the water column where GL and/or BL-enriched environment prevails. However, decreased fitness is offset by increased lipid content and elongated cellular morphology.