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Antigen 84, an Effector of Pleiomorphism in Mycobacterium smegmatis

Department of Molecular Biology and Microbiology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106,¹ Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland,² Life Sciences Centre, University of British Columbia, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada³

Received 9 May 2007/ Accepted 23 August 2007

While in most rod-shaped bacteria, morphology is based on MreB-like proteins that form an actin-like cytoskeletal scaffold for cell wall biosynthesis, the factors that determine the more flexible rod-like shape in actinobacteria such as Mycobacterium species are unknown. Here we show that a Mycobacterium smegmatis protein homologous to eubacterial DivIVA-like proteins, including M. tuberculosis antigen 84 (Ag84), localized symmetrically to centers of peptidoglycan biosynthesis at the poles and septa. Controlled gene disruption experiments indicated that the gene encoding Ag84, wag31, was essential; when overexpressed, cells became longer and wider, with Ag84 asymmetrically distributed at one pole. Many became grossly enlarged, bowling-pin-shaped cells having up to 80-fold-increased volume. In these cells, Ag84 accumulated predominantly at a bulbous pole that was apparently generated by uncontrolled cell wall expansion. In some cells, Ag84 was associated with exceptional sites of cell wall expansion (buds) that evolved into branches. M. bovis BCG Ag84 was able to form oligomers in vitro, perhaps reflecting its superstructure in vivo. These data suggested a role for Ag84 in cell division and modulating cell shape in pleiomorphic actinobacteria.

Published ahead of print on 31 August 2007.

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