Comparative metabolomic analysis of the effects of light quality on polysaccharide production of cyanobacterium Nostoc flagelliforme

Light quality strongly affects cell growth and polysaccharide production of cyanobacteria, however, the metabolic mechanism of polysaccharide biosynthesis upon light quality has not been fully explored yet. The effects of light quality on the metabolic changes of Nostoc flagelliforme were comprehensively investigated using red, yellow, green, blue, purple light emitting diodes for illumination. The principal component analysis revealed that red, yellow, green, blue, and purple light-grown cells were metabolically distinct from those illuminated with white fluorescent light, and the influence of light quality on metabolism was particularly dependent on light wavelength. Significant correlations between the metabolic profile and extracellular polysaccharide (EPS) and capsular polysaccharide (CPS) production were revealed by partial least-squares to latent structure analysis respectively, and analysis of key metabolites showed that CPS production was closely related with cell growth while the biosynthesis of EPS was more closely related with light conditions. Furthermore, as the influence pattern of red light on cellular metabolism and polysaccharide production was quite different from other light conditions, the effects of intensity of red light on photosynthesis and polysaccharide production were evaluated, and the results revealed that red light induced photoinhibition and therefore stimulated polysaccharide production. Manipulation of red light was thus proposed to profitably enhance polysaccharide productivity of N. flagelliforme.