Relation between excreted lipopolysaccharide complexes and surface structures of a lysine-limited culture of Escherichia coli.

Knox, K. W. (Twyford Laboratories, London, England), Maret Vesk, and Elizabeth Work. Relation between excreted lipopolysaccharide complexes and surface structures of a lysine-limited culture of Escherichia coli. J. Bacteriol. 92:1206-1217. 1966.-The lysine-requiring mutant Escherichia coli 12408, when grown in 15 liters of defined medium containing a suboptimal amount of lysine, showed a biphasic type of growth. During a long stationary phase of 15 hr, there was a steady accumulation of diaminopimelic acid (DAP) and an antigenic complex of lipopolysaccharide (LPS) and lipoprotein; the accumulation continued unchanged until the end of the second growth phase. The rapid rate of DAP excretion suggested that it was the result of a derepressed state of a biosynthetic pathway. LPS excretion was such that the amount in the culture fluid was doubled during a period corresponding to the normal generation time for the organism; this suggested that the LPS-lipoprotein complex was a product of unbalanced growth. Surface defects were suggested by the action of lysozyme, which, in low concentrations (10 mug/ml), lysed the lysine-limited cells even in the absence of ethylenediaminetetraacetic acid, but had no effect at 10 mug/ml on cells grown with adequate lysine. Electron microscopy of cells excreting the LPS complex showed them to be surrounded by a mass of stacked leaflets and globules, some of which were bounded by triple membranes. Sections showed no lysis but changes in cell surfaces; outer layers of the walls had numerous blebs whose outer membranes were sometimes continuous with the outer triple membrane of the wall. LPS-lipoprotein probably originates from these blebs.