The role of murein hydrolases in the cell division of Escherichia coli

• Main Author: Edwards, David Hugh
• Published: University of Edinburgh 1993
• Subjects: 571.29
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.649903

<I>Escherichia coli</I> is a Gram-negative rod shaped bacterium that grows by lateral elongation before forming a septum at its centre and dividing into two daughter cells. During growth and division the cell's shape and integrity are maintained by a rigid cell wall or murein sacculus. This sacculus is essentially, a monolayer constructed from repeated peptidoglycan sub-units. The synthesis and hydrolysis of the cell wall is mediated by a number of enzymes, including a class of penicillin-sensitive proteins, the PBPs. One of these, PBP3, is a septum specific peptidoglycan synthetase. The work in this thesis is concerned with suppression to a temperature sensitive mutation (<I>ftsI</I>23) in the gene for PBP3. It is shown that <I>FtsI</I>23 can be suppressed by increased levels of the cell's major DD-carboxypeptidases, PBP5 and PBP6. A second known suppressor of <I>ftsI</I> mutations, <I>sufI</I>, is also shown to suppress <I>ftsI</I>23 by increasing the levels of PBP6 and membrane bound DD-carboxypeptidase activity. These results are proposed to indicate that PBP3 has a preference for 'tripeptide acceptors' as substrate. In conjunction with murein analysis of <I>ftsI</I>23 suppressed strains, it is further proposed that these acceptors are necessary for the formation of a set of critical but temporary 'tetrapeptide-tripeptide' cross-bridges. These cross-bridges are envisaged to be required for the incorporation of nascent peptidoglycan at the septum. To investigate this further a strain lacking all known periplasmic DD-carboxypeptidases was constructed. In addition the approximate locations of the gene for the LD-carboxypeptidase and <I>dacC</I> were mapped to 37 minutes and 19 minutes, respectively. It is also shown that strains completely lacking another peptidoglycan synthetase, RodA, grow as stable, mecillinam resistant spheres.