~~~~~In a comprehensive survey of the carbohydrate accumulation profiles of more than 70 strains of cyanobacteria three organic osmotica (glucosylglycerol, sucrose and trehalose) have been identified in both freshwater and marine isolates under conditions of osmotic stress. While the trend was towards glucosylglycerol accumulation in marine strains and sucrose accumulation in freshwater forms, there were no absolute differences between cyanobacteria isolated from each habitat. There was also no clear link between genus and the type of carbohydrate accumulated.

A potent inhibitor of seryl tRNAsynthetase, designated SB-217452 has been isolated from Streptomyces sp. ATCC 700974. The fermentation, isolation, structure elucidation and some properties are described. SB-217452 showed inhibitory activity against both Staphylococcus aureus and rat seryl tRNA synthetases, with similar IC50 values of approximately 8 nM. The inhibitor is the serine linked nucleoside moiety of the antibiotic albomycin 82. In contrast to albomycin 52, SB-217452 showed only very weak antibacterial activity against a limited range of microorganisms. The compoundhas not been previously reported as a naturally occurring metabolite. In addition to SB-217452, albomycin S2 Fe3+ complex and the novel Al3+ complex were isolated from the fermentation. These complexes had no seryl tRNAsynthetase inhibitory activity. Aminoacyl-tRNA synthetases catalyze one of the most critical steps in protein biosynthesis. They attach one of twenty amino acids to one of about sixty tRNAs. Their specificities with regard to amino acids and tRNAs are responsible for the accurate primary structures of proteins. The enzymes are essential for cell viability, and are

Transfer of Synechocystis PCC6714 from a freshwater medium to a saline medium caused the cells to shrink; rapid entry of NaCl resulted in a partial recovery of cellular volume within 2 min. Active extrusion of internal Na+ in exchange for extracellular K+ then occurred (within 20 min). Finally, the low‐Mr carbohydrates sucrose and glucosylglycerol were accumulated and internal KC1 levels declined. In long‐term growth experiments, the relative importance of sucrose as a component of the low‐Mr organic solute fraction decreased and glucosylglycerol became the single most important intracellular solute. These observations demonstrate that several inorganic and organic solutes are involved in osmotic adjustment in this cyanobacterium, with sequential changes in the relative importance of each solute following transfer to a saline medium.

The filamentous cyanobacterium Spirulina platensis has been examined for salt tolerance and osmotic adjustment. Salinities up to 150% seawater had little effect on growth yield or photosynthetic O2 evolution; higher salinities were markedly inhibitory. Osmotic adjustment was achieved by the intracellular accumulation of the low-molecular-weight carbohydrate glucosyl-glycerol in response to increased external salinity: in fullstrength (100%) seawater glucosyl-glycerol accounted for approximately 5.0% of the dry weight of the cyanobacterium. Trehalose was also present, particularly in cells at low salt concentration, and in 50% seawater medium accounted for up to 1.0% of the dry weight of the cyanobacterium. For cells grown in 100% seawater the ratio of trehalose to glucosyl-glycerol varied with temperature: at 37°C trehalose comprised 31% (w/w) of the low-molecular-weight carbohydrates while at 20°C only 9% of the total was trehalose. When subjected to hypo-osmotic shock the intracellular concentration of glucosyl-glycerol decreased and this was mirrored by an increase in glycogen. An understanding of the osmotic adjustment of S. platensis has implications both for the mass culturing of this and other strains of Spirulina and possibly also for the quality of the harvested product.

Three groups of cyanobacteria are recognized on the basis of their organic osmotica and upper salinity limit for growth. In general, the least halotolerant forms accumulate disaccharides, while cyanobacteria of intermediate halotolerance synthesize the heteroside glucosylglycerol and the most halotolerant isolates accumulate betaines in response to salt stress. However, certain strains also accumulate additional organic solutes, depending upon the growth temperature, the ambient salinity and the duration of salt stress.