Looking Outwards: Isolation of Cyanobacterial Released Carbohydrate Polymers and Proteins

Cyanobacteria can actively secrete a wide range of biomolecules into the extracellular environment, such as heteropolysaccharides and proteins. The identification and characterization of these biomolecules can improve knowledge about their secretion pathways and help to manipulate them. Furthermore, some of these biomolecules are also interesting in terms of biotechnological applications. Described here are two protocols for easy and rapid isolation of cyanobacterial released carbohydrate polymers and proteins. The method for isolation of released carbohydrate polymers is based on conventional precipitation techniques of polysaccharides in aqueous solutions using organic solvents. This method preserves the characteristics of the polymer and simultaneously avoids the presence of contaminants from cell debris and culture medium. At the end of the process, the lyophilized polymer is ready to be used or characterized or can be subjected to further rounds of purification, depending on the final intended use. Regarding the isolation of the cyanobacterial exoproteome, the technique is based on the concentration of the cell-free medium after removal of the major contaminants by centrifugation and filtration. This strategy allows for reliable isolation of proteins that reach the extracellular milieu via membrane transporters or outer membrane vesicles. These proteins can be subsequently identified using standard mass spectrometry techniques. The protocols presented here can be applied not only to a wide range of cyanobacteria, but also to other bacterial strains. Furthermore, these procedures can be easily tailored according to the final use of the products, purity degree required, and bacterial strain.