Analysis of protein expression in response to osmotic stress in Escherichia coli

Two strains of Escherichia coli isogenic except for the cya (adenylate cyclase) allele were grown with [35S]methionine and cysteine in minimal defined glucose medium and in this medium with 600 mM NaCl to induce osmotic stress. Cells were grown for approximately two generations. The labeled proteins were separated by 2‐dimensional electrophoresis and were quantified fluorographically. Of the 263 major proteins (proteins incorporating 0.10% or more of the total radioactivity) in the cya+ control culture, radioactivity in 41 proteins was at least ten times greater in cells grown with osmotic stress. Six of these individual proteins each accounted for 1.0% or more of the total radioactive label in the cells. Conversely, radioactivity in 31 major proteins appeared to decrease at least ten times when cells grew with osmotic stress. These data indicate that the response of the bacterium to osmotic stress involves induction of some proteins and repression of others. 61% of the proteins that appear to be stimulated by salt stress were found in both strains indicating there is no obligatory requirement for cAMP.