The effects of hypersaline treatment (osmotic upshock) on solute accumulation have been studied in the Grampositive bacterium BaciZZus subtiZis. Natural abundance 3C NMR spectroscopy studies revealed only proline as a major organic osmoticum in cells grown in defined medium (no exogenous organic solutes) and this finding was confirmed by amino acid analysis. Intracellular concentrations of both K+ and proline rose markedly after osmotic upshock. K+ influx from the medium was rapid (< 1 h) but proline synthesis was a slower process (5-9 h). Proline synthesis appeared to be dependent on the prior accumulation of K+ and it is possible that K+ serves in some manner as the signal for increased proline synthesis. In cells upshocked in medium enriched in glycine betaine the endogenous synthesis of proline was repressed and glycine betaine served as the sole organic osmoticum. K+ was also accumulated under these conditions.

The effects of hypersaline treatment (osmotic upshock) on cell water relations were examined in the Gram-positive bacterium Bacillus subtilis using particle size analysis. Application of the Boyle-van't Hoff relationship (cell volume versus reciprocal of external osmolality) permitted direct determination of turgor pressure, which was approximately 0.75 osmol kg-' (1.9MPa) in exponentially growing bacteria in a defined medium. The abolition of turgor pressure immediately after upshock and the subsequent recovery of turgor were investigated. Recovery of turgor was K+ dependent. Calculation of turgor by an alternative method involving spectrophotometric analysis of shrinkage gave somewhat lower estimates of turgor pressure.

~~~~~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.

No abstract

No abstract