The goal of this work was to evaluate the protective effect of glycerol and PEG-methyl ether methacrylate (PEGMA) coatings, as well as CaCl2 concentration, on the viability of alginate-immobilized Synechococcus elongatus after cold storage. Neither the growth rate nor the generation time of alginate-immobilized S. elongatus was affected by the concentration of CaCl2 after cold preservation by refrigeration at 4 °C for 3.4 years (p > 0.05). However, the type and concentration of the coating, glycerol, or PEGMA, of the alginate beads, affected both growth rate and generation time (p < 0.05). In addition, significant differences in the production of S. elongatus cells were found due to the CaCl2 concentration (p < 0.05), type of coating (p < 0.05), and the concentration of the coating (p < 0.05). Increase in glycerol or PEGMA content was directly related to the decrease in chlorophyll a content, except for 4% CaCl2 concentration with glycerol coating, which did not show an apparent trend. Chlorophyll a content had an inverse trend with respect to growth rate only for 2% CaCl2 concentration, while carotenoid content was not affected. We conclude that S. elongatus cells continue being able to grow and to produce new cells, even after 3.4 years of cold storage as free cultures, or alginate-immobilized and cross-linked with 2 or 4% CaCl2, or when coated with glycerol or PEGMA. Moreover, production of cells and growth rate increased as the concentration of glycerol or PEGMA increased. Particularly, higher production of cells was observed for cold-preserved alginate-immobilized S. elongatus, coated with PEGMA.
