whmD is an essential mycobacterial gene required for proper septation and cell division

James E. Gomez* and
William R. Bishai*,†,‡,§

Departments of ^*Molecular Microbiology and Immunology, ^†International Health, and ^‡Medicine, Center for Tuberculosis Research, The Johns Hopkins University, Baltimore, MD 21205

Communicated by Thomas J. Kelly, Johns Hopkins University, Baltimore, MD (received for review January 28, 2000)

Abstract

A study of potential mycobacterial regulatory genes led to the isolation of the Mycobacterium smegmatis whmD gene, which encodes a homologue of WhiB, a Streptomyces coelicolor protein required for sporulation. Unlike its Streptomyces homologue, WhmD is essential in M. smegmatis. The whmD gene could be disrupted only in the presence of a plasmid supplying whmD in trans. A plasmid that allowed chemically regulated expression of the WhmD protein was used to generate a conditional whmD mutant. On withdrawal of the inducer, the conditional whmD mutant exhibited irreversible, filamentous, branched growth with diminished septum formation and aberrant septal placement, whereas WhmD overexpression resulted in growth retardation and hyperseptation. Nucleic acid synthesis and levels of the essential cell division protein FtsZ were unaltered by WhmD deficiency. Together, these phenotypes indicate a role for WhmD in mycobacterial septum formation and cell division.

Footnotes

↵ § To whom reprint requests should be addressed at: Center for Tuberculosis Research, The Johns Hopkins School of Hygiene and Public Health, 615 North Wolfe Street, Room 5031C, Baltimore, MD 21205. E-mail: wbishai{at}jhsph.edu.
The sequence reported in this paper has been deposited in the GenBank database (accession no. AF164439).
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.140225297.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.140225297
Abbreviations:

Suc,

sucrose;

Hy,

hygromycin;

Km,

kanamycin;

Am,

apramycin;

superscript S,

sensitivity;

superscript R,

resistance;

DIC,

differential interference contrast