Measuring turgor pressure in bacterial cells: effects of osmolality of growth and nutrient conditions

Bacteria generally maintain high osmotic pressure differences across their cell walls (~1-20 atm). This pressure difference, called turgor, requires specialized machinery that balances the cytoplasmic osmolyte concentration against the embedding medium. Details of this machinery as well as the roles of the components of the multilayer cell wall are not well understood. Directly measuring turgor has been an experimental challenge, and a rapid, precise method has been lacking. We here present an experimental method based on force spectroscopy (AFM) to quantify turgor and its variations at a single cell level. We measured turgor for gram-negative and gram-positive species as well as the effect of growth conditions and nutrient concentrations.