A MAJOR AUTOLYSIN OF PSEUDOMONAS-AERUGINOSA - SUBCELLULAR-DISTRIBUTION, POTENTIAL ROLE IN CELL-GROWTH AND DIVISION, AND SECRETION IN SURFACE-MEMBRANE VESICLES

A 26-kDa murein hydrolase is the major autolysin of Pseudomonas aerugi nosa PAO1, and its expression can be correlated with the growth and di vision of cells in both batch and synchronously growing cultures. In b atch cultures, it is detected primarily during the mid-exponential gro wth phase, and in synchronous cultures, it is detected primarily durin g the cell elongation and division phases. Immunogold labeling of thin sections of P. aeruginosa using antibodies raised against the 26-kDa autolysin revealed that it is associated mainly,vith the cell envelope and in particular within the periplasm. It is also tightly bound to t he peptidoglycan layer, since murein sacculi, isolated by boiling 4% s odium dodecyl sulfate treatment, could also be immunogold labeled. Sin ce division is due to cell constriction in this P. aeruginosa strain ( septa are rarely seen), we cannot comment on the autolysin's contribut ion to septation, although constriction sites were always heavily labe led. Some labeling was also found in the cytoplasm, and this was thoug ht to be due to the de novo synthesis of the enzyme before translocati on to the periplasm. Interestingly, the autolysin was also found to be associated with natural membrane vesicles which blebbed from the surf ace during cell growth; the enzyme is therefore part of the complex ma keup of these membrane packages of secreted materials (J.L. Kadurugamu wa and T.J. Beveridge, J. Bacteriol. 177:3998-4008, 1995). The express ion of these membrane vesicles was correlated with the expression of B -band lipopolysaccharide.