GROWTH AND ORGANIC OSMOLYTES OF GEOGRAPHICALLY DIFFERENT ISOLATES OF MICROCOLEUS-CHTHONOPLASTES (CYANOBACTERIA) FROM BENTHIC MICROBIAL MATS- RESPONSE TO SALINITY CHANGE

The comparative growth and osmotic acclimation of ten culture strains of the marine benthic cyanobacterium Microcoleus chthonoplastes Thuret isolated from microbial mats in Germany, Spain, Egypt, the United Sta tes, Mexico, Chile, and Australia were investigated in salinities rang ing from freshwater to twice seawater. All isolates showed a broad gro wth versus salinity response consistent with the dominance of this spe cies in intertidal and hypersaline microbial communities. Growth optim a, salinity preferences, and maximum growth rates differed for each is olate and could be related to the habitat from which they were isolate d. This is most obvious when comparing strains from brackish habitats with those from a hypersaline lake. While the former isolates exhibite d sharply pronounced growth optima under hyposaline conditions, cultur es from the hypersaline environment grew best in salinity more than do uble seawater. The major low-molecular weight organic compounds presen t in all M. chthonoplastes strains were the carbohydrates glycosylglyc erol and trehalose. This was proven by using C-13-nuclear magnetic res onance spectroscopy. Glycosylglycerol was synthesized and accumulated with increasing salinities, indicating its role as an osmolyte. In con trast, trehalose was present in relatively high concentrations under h yposaline conditions only. Differences in the patterns of growth versu s salinity, as well as in those of osmotic acclimation among the M. ch thonoplastes isolates, point to the development of different physiolog ical ecotypes within the species.