Organic Osmoregulatory Solutes in Cyanobacteria

The major organic osmoregulatory solutes of 36 cyanobacteria from a wide range of environmental sources have been examined using 13C nuclear magnetic resonance spectroscopy. These strains were also examined for their salt-tolerance, and could be arranged in three salt-tolerance groups, designated freshwater, marine and hypersaline. The most salt-tolerant cyanobacteria in the hypersaline group are properly classified as moderately halophilic. Cyanobacteria from all habitats and taxonomic groups accumulated organic osmoregulatory solutes, and the chemical class of the solute correlated with the salt-tolerance and habitat of the strain. Freshwater strains accumulated simple saccharides, predominantly sucrose and trehalose; marine strains accumulated the heteroside O-α-d-glucopyranosyl-(1→2)-glycerol, and hypersaline strains accumulated sucrose and/or trehalose together with glycine betaine or the novel solute l-glutamate betaine (N-trimethyl-l-glutamate) or they accumulated glycine betaine alone. The results suggest that the presence of certain major organic osmoregulatory solutes may be useful in the numerical taxonomy of cyanobacteria, and in the identification of some ionic characteristics of the environment of origin of each isolate.