Roles of pneumococcal DivIB in cell division

Laboratoire d'Ingénierie des Macromolécules, Institut de Biologie Structurale (Université Joseph Fourier, CNRS UMR 5075, CEA), Grenoble, France; and Dipartimento di Scienze e Tecnologie Biomediche, Sez. Microbiologia Medica, Università di Cagliari, Italy

^* To whom correspondence should be addressed. Email: thierry.vernet{at}ibs.fr.

	Abstract

DivIB is a division protein conserved in most eubacteria, also known as FtsQ in Gram negative organisms. DivIB is localized at the division site and forms a complex with two other division proteins, FtsL and DivIC/FtsB. The precise function of these three bitopic membrane proteins that are central to division process remains unknown. We report here the characterization of a divIB deletion mutant in Streptococcus pneumoniae, which is a coccus that divides with parallel planes. Unlike its homologue FtsQ in Escherichia coli, pneumococcal DivIB is not required for growth in rich medium, but the divIB mutant forms chains of diplococci and a small fraction of enlarged cells with defective septa. However, the deletion mutant does not grow in a chemically defined medium. In the absence of DivIB and protein synthesis, the partner FtsL is rapidly degraded, whereas other division proteins are not affected, pointing to a role of DivIB in stabilizing FtsL. This is further supported by the finding that an additional copy of ftsL restores growth of the divIB mutant in defined medium. Functional mapping of the three distinct -, -, and -domains of the extracellular region of DivIB revealed that a complete -domain is required to fully rescue the deletion mutant. DivIB with a truncated -domain reverts only the chaining phenotype, indicating that DivIB has distinct roles early and late in the division process. Most importantly, the deletion of divIB increases the susceptibility to -lactams, more evidently in a resistant strain, suggesting a function in cell wall synthesis.