Antigen 84, an Effector of Pleiomorphism inMycobacterium smegmatis

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Abstract
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 asMycobacteriumspecies are unknown. Here we show that aMycobacterium smegmatisprotein homologous to eubacterial DivIVA-like proteins, includingM. tuberculosisantigen 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. bovisBCG 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.