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J. Bacteriol. doi:10.1128/JB.00044-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The role of PBP1 in the cell division of Staphylococcus aureus

Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica (ITQB) da Universidade Nova de Lisboa (UNL), 2780 Oeiras, Portugal; Laboratory of Microbial Development, ITQB-UNL, 2780 Oeiras, Portugal; Laboratory of Bacterial Cell Biology, ITQB-UNL, 2780 Oeiras, Portugal; Laboratory of Microbiology, The Rockefeller University, 1230 York Avenue, New York, NY 10021

^* To whom correspondence should be addressed. Email: tomasz{at}mail.rockefeller.edu.

	Abstract

We constructed a conditional mutant of pbpA in which transcription of the gene was placed under the control of an IPTG inducible promoter - in order to explore the role of PBP1 in growth, cell wall structure and cell division. A methicillin resistant and an isogenic methicillin susceptible strain each carrying the pbpA mutation could not grow in the absence of the inducer. Conditional mutants of pbpA transferred into IPTG-free medium underwent a four to five fold increase in cell mass, which was not accompanied by a proportional increase in viable titer. Examination of thin sections of such cells by transmission electron microscopy or fluorescent microscopy of intact cells with Nile red stained membranes showed a morphologically heterogeneous population of bacteria with abnormally increased size, distorted axial ratios and a deficit in the number of cells with completed septa. Immunofluorescence with an antibody specific for PBP1 localized the protein to sites of cell division. No alteration in the composition of peptidoglycan was detectable in pbpA conditional mutants grown in the presence of a sub-optimal concentration of IPTG, which severely restricted the rate of growth and the essential function of PBP1 could not be replaced by PBP2A present in methicillin resistant cells. The observations suggest that PBP1 is not a major contributor to the crosslinking of peptidoglycan and its essential function must be intimately integrated in the mechanism of cell division.

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