No abstract

A novel photo protective mycosporine was isolated from the lichenized ascomycete Collema cristatum. Biological activity was measured in terms of protection against UV‐B induced membrane destruction and pyrimidine dimer formation in cultured human keratinocytes, and prevention of UV‐B induced erythema. It was found that the pure isolated compound prevented UV‐B induced cell destruction in a dose‐dependent manner, that the compound partially prevented pyrimidine dimer formation and completely prevented UV‐B induced erythema when applied to the skin prior to irradiation.

Dimethyl sulfide, the most important form of sulfur gas, is formed by bacterial degradation of dimethylsulfoniopropionate (DMSP) in the Lake of Galilee. DMSP is believed to be a methionine metabolite produced by marine algae and higher plants as part of their osmoregulatory systems. Until now, this process was found exclusively in saline water and therefore was regarded as insignificant for the formation of DMS in freshwaters. It is hereby demonstrated that the process can be dominant in freshwater systems as well, and its product can even affect the odor quality of some drinking and recreational water systems. Peridinium gatunense, a freshwater dinoflagellate which dominates the phytoplankton population in the lake during the winter-spring season, stores a considerable amount (up to 5.5 pg/cell) of DMSP. P. gatunense growth curves reveal an increased storage of DMSP toward the stationary and declining growth phases. The DMSP undergoes bacterial and chemical degradation to release DMS. Released fluxes of DMS from the Lake of Galilee are estimated to be in the range of 0.1 mmol/m 2 month during the late period of the Peridinium bloom season.

Hydroxy, n-saturated, branched, dioic, and unsaturated fatty acids in six freshwater wild cyanobacteria (Chroococcus minutus, Lyngbya ceylanica, Merismopedia glauca, Nodularia sphaerocarpa, Nostoc linckia, and Synechococcus aeruginosus) collected from different lakes and springs of Israel have been identified by gas chromatography-mass spectrometry (GC-MS).

We present the first observations on the occurrence of inorganic polysulfides in an oxygen rich aquatic system. Inorganic polysulfides were found both in the hypolimnion and the epilimnion of a freshwater lakesLake Kinneret. The presence of these compounds in oxic systems resolves the enigma concerning the mechanism of formation of dimethyl disulfide, dimethyltrisulfide, and dimethyltetrasulfide in oxygen rich aquatic systems and marine water. The abundance of low molecular weight organic and inorganic polysulfides relative to the a priori postulated dominance of the pentasulfide family is explained by the low level of polysulfides in oxygen-rich aquatic systems. Thermodynamic calculations show that for trace levels of reduced sulfur compounds, dimethyl disulfide becomes the dominant polysulfide form.