An extracellular lipopolysaccharide-phospholipid-protein complex produced by Escherichia coli grown under lysine-limiting conditions

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Abstract
Lysine limitation during growth of the lysine-requiring mutant of E. coli resulted in the excretion of a complex containing 60 percent of lipopolysaccharide, 26 percent of extractable phospholipid and 11 percent protein. The complex was obtained from the culture filtrate in yields of about 0.5 g/1 by precipitation with chloroform or gel filtration; some purification steps are described. The greater part of the phospholipid consisted of phosphatidyl-ethanolamine, which contained four main fatty-acids; two monoenoic acids and a cyclopropane acid were esterified mainly in the [beta]-position, and a saturated acid was located mainly in the [gamma]-position. The protein component was relatively insoluble and contained an excess of acidic over basic amino acids and little cystine. The lipopolysaccharide resembled in composition the intracellular lipopolysaccharides from rough strains of E. coli. Both protein and lipopolysaccharide constituents of the complex were serologically active; the complex was less toxic than the purified lipopolysaccharide. In the electron microscope the complex showed a mixture of particles of various sizes and shapes. Rods and hollow spheroids (diameter 12-200mu) were most common and resembled the particles previously found surrounding cells actively excreting the complex. The chloroform-precipitated material showed a tubular lamellar structure. Soluble lipopolysaccharide prepared from the complex also consisted of hollow spheres and rods.