Covalent linkage of lipoprotein to peptidoglycan is not essential for outer membrane stability in Proteus mirabilis.

Isolated rigis layers from Proteus mirabilis harvested at different growth phases were degraded by endo-N-acetylmuramidase from Chalaropsis B, and the degradation products were investigated. The results show the complete absence of covalently linked lipoprotein in exponential-phase cultures. Stationary cells, however, possess covalently linked lipoprotein in amounts similar to those found in Escherichia coli or Salmonella typhimurium during all growth phases. The overall peptidoglycan structure did not change during transition from logarithmic to stationary growth. Implications of these findings for the organization of the outer membrane are discussed.