MYCOSPORINE-LIKE AMINO-ACIDS AS OSMOTIC SOLUTES IN A COMMUNITY OF HALOPHILIC CYANOBACTERIA

Large concentrations of mycosporine-like amino acids (MAAs) were found in a community of unicellular cyanobacteria inhabiting a gypsum crust developing on the bottom of a hypersaline saltern pond in Eilat, Isra el. This is the first report of the occurrence of MAAs in a halophilic cyanobacterial community. Two MAAs were detected one with an absorpti on maximum at 332 nm, and one at 362 nm. Intracellular MAA concentrati ons in the cyanobacterial community were estimated to be at least 98 m M, and this already high value is probably an underestimation With an average molecular weight of around 300, MAAs should contribute at leas t 3% of the cell wet weight. While MAAs have been shown to absorb ultr aviolet (UV) radiation, protecting the cells against solar radiation, they may also have an osmotic function in cyanobacterial communities i nhabiting hypersaline environments, and help the cells to cope with th e high salt concentrations in their environment. When the upper layer of the gypsum crust was subjected to dilution with distilled wafer, MA As rapidly appeared in the outer medium, with the extent of loss of in tracellular MAAs being approximately proportional to the extent of the dilation stress applied. No uptake of MAAs was observed in response t o a subsequent increase in medium salinity.