A new strategy for a combined isolation of EPS and pigments from cyanobacteria

Cyanobacteria obtain their energy through photosynthesis and live embedded in a matrix of extracellular polymeric substances (EPS) containing valuable products, e.g., polysaccharides, lipids, proteins, and antimicrobials. Besides chlorophyll a and carotenoids, they have light-absorbing compounds in the form of light-harvesting complexes, the so-called phycobilisomes, consisting of different phycobiliproteins. Together they close the “green gap” whereby cyanobacteria can use light more effective than higher plants. Cultivation of cyanobacteria on a lab-scale results in small amounts of biomass for their characterization or a comprehensive screening. EPS are, for example, produced as a protection against suboptimal culture conditions. Carotenoids are essential light-harvesting pigments for photosynthesis, play a key role in photoprotective reactions, and are produced for cell wall stabilization. Essentially, the pigment composition of cyanobacteria depends on the available light spectrum, nitrogen content, and temperature. Especially the production of EPS and pigments are indicators for the cell-condition. Therefore, different EPS extraction methods were tested including the determination of inhibitory effects of extracts against Escherichia coli. Based on the best EPS extraction method, a new strategy for downstream processing (DSP) was developed to determine EPS, the pigments chlorophyll a and carotenoids, and phycobiliproteins from only one sample. As cyanobacterial model organisms Trichocoleus sociatus and Nostoc flagelliforme were used, and DSP strategy was successfully transferred to four additional cyanobacteria. The final DSP includes the following steps: (i) EPS extraction, (ii) lyophilization of biomass, (iii) extraction of phycobiliproteins, and a final (iv) chlorophyll a and carotenoid extraction. The new strategy allows a comprehensive characterization of cyanobacterial cells.