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Journal of Bacteriology, May 2009, p. 3108-3119, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.01737-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

A Vitamin B12-Based System for Conditional Expression Reveals dksA To Be an Essential Gene in Myxococcus xanthus {triangledown}

Diana García-Moreno,1 María Carmen Polanco,1 Gloria Navarro-Avilés,1,{dagger} Francisco J. Murillo,1 S. Padmanabhan,2 and Montserrat Elías-Arnanz1*

Departamento de Genética y Microbiología, Área de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia 30100, Spain,1 Instituto de Química Física Rocasolano, Consejo Superior de Investigaciones Científicas, Serrano 119, 28006 Madrid, Spain2

Received 11 December 2008/ Accepted 17 February 2009

Myxococcus xanthus is a prokaryotic model system for the study of multicellular development and the response to blue light. The previous analyses of these processes and the characterization of new genes would benefit from a robust system for controlled gene expression, which has been elusive so far for this bacterium. Here, we describe a system for conditional expression of genes in M. xanthus based on our recent finding that vitamin B12 and CarH, a MerR-type transcriptional repressor, together downregulate a photoinducible promoter. Using this system, we confirmed that M. xanthus rpoN, encoding {sigma}54, is an essential gene, as reported earlier. We then tested it with ftsZ and dksA. In most bacteria, ftsZ is vital due to its role in cell division, whereas null mutants of dksA, whose product regulates the stringent response via transcriptional control of rRNA and amino acid biosynthesis promoters, are viable but cause pleiotropic effects. As with rpoN, it was impossible to delete endogenous ftsZ or dksA in M. xanthus except in a merodiploid background carrying another functional copy, which indicates that these are essential genes. B12-based conditional expression of ftsZ was insufficient to provide the high intracellular FtsZ levels required. With dksA, as with rpoN, cells were viable under permissive but not restrictive conditions, and depletion of DksA or {sigma}54 produced filamentous, aberrantly dividing cells. dksA thus joins rpoN in a growing list of genes dispensable in many bacteria but essential in M. xanthus.

* Corresponding author. Mailing address: Departamento de Genética y Microbiología, Área de Genética (Unidad Asociada al IQFR-CSIC), Facultad de Biología, Universidad de Murcia, Murcia 30100, Spain. Phone: 34 968 367134. Fax: 34 968 363963. E-mail: melias{at}um.es

{triangledown} Published ahead of print on 27 February 2009.

{dagger} Present address: Department of Environmental Protection, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain.

Journal of Bacteriology, May 2009, p. 3108-3119, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.01737-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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