Purification and analysis of expression of the stationary phase-inducible slp lipoprotein in Escherichia coli: role of the Mar system.

Entrance into the stationary phase in Escherichia coli induces a group of stress response genes including slp, which encodes an outer membrane lipoprotein. Glucose limitation is sufficient, but not necessary, for the increase in slp expression. The Slp protein was purified and an antibody-based assay was developed, which enabled identification of Slp as spot R2226 (G018.1) in the E. coli gene-protein database. Although Slp is a major membrane component in stationary phase cultures grown in complex medium, no significant changes in resistance to oxidative stress or membrane perturbants were found in a slp null mutant strain. The presence or absence of multiple antibiotic resistance (Mar) A did not alter the final stationary phase levels of Slp. However, the Mar system could modestly influence the level of slp expression during the transition from exponential to stationary growth phase. Accumulation of Slp leads to a small increase in sensitivity to chloramphenicol.