The Effect Of LPS On The Outer Membranes Of Escherichia Coli Cell

Lipopolysaccharide (LPS) is the main component in most outer membrane of Gram negative bacteria. Escherichia coli is a model microorganism of gram-negative bacteria. Here, the effect of LPS on the outer membrane of E. coli was systematically studied. Seven E. coli mutant strains which can make different LPS structures were used. E. coli W3110 and E. coli W3110/pWSK29 were used as control. The alterations of LPS structure were verified by TLC and ESI/MS. The effects of LPS structure on the cell growth, the permeability of cell outer membrane, and the ability to form biofilm were investigated. The main results are listed below.(1) LPS and its main component lipid A were extracted and assayed by using TLC and ESI/MS. The results showed that LPS structures were changed as expected in all mutants. The degree of modification on LPS is high in all E. coli mutant strains except for W3110/pWSK29-LpxF and W3110/pWSK29-PagP. The growth curves of all E. coli strains showed no big difference.(2) The membrane permeability of all E. coli strains was analyzed by using N-phenyl-1-naphthylamine (NPN) fluorescent probe. The outer membrane permeability is strongly related to the exact structure of LPS. Wild-type E. coli showed the least permeability, while mutants in which the phosphate groups, acyl chains and polysaccharide of LPS were changed showed higher permeability. The chain length of the polysaccharide has the largest effect, followed by the number of the acyl chains. This conclusion was further confirmed by the minimum inhibitory concentrations assay and theβ-lactamase activity assay. Strains which showed higher permeability were more sensitive to antibiotics and degraded more ampicillin.(3) The biofilm formation all E. coli strains were investigated. It was found that the modifications on the polysaccharide and acyl chains of LPS inhibit the biofilm formation, and the modifications on the phosphate groups of LPS enhance the biofilm formation. The hydrophobicity and autoaggregation assays were also performed. The data showed that there are some relationships between the hydrophobicity and biofilm formation.(4) The relationship between LPS structure and outer membranes was analyzed by synthesis. It was suggesting that the more the membrane permeability is, the less the biofilm form. The chain length of the polysaccharide has the largest effect on all the outer membranes, followed by the number of the acyl chains.This research carried out the systematic study on the relationship between the outer membrane permeability, biofilm formation and LPS structure. This research would be important for redesigning the outer membrane structure of industrial microorganism and for detecting and controlling Gram-negative bacterial pathogens.