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Journal of Bacteriology, June 2009, p. 3712-3716, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.01678-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

A Role for Single-Stranded Exonucleases in the Use of DNA as a Nutrient{triangledown}

Vyacheslav Palchevskiy{dagger} and Steven E. Finkel*

Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2910

Received 1 December 2008/ Accepted 19 March 2009

Nutritional competence is the ability of bacterial cells to utilize exogenous double-stranded DNA molecules as a nutrient source. We previously identified several genes in Escherichia coli that are important for this process and proposed a model, based on models of natural competence and transformation in bacteria, where it is assumed that single-stranded DNA (ssDNA) is degraded following entry into the cytoplasm. Since E. coli has several exonucleases, we determined whether they play a role in the long-term survival and the catabolism of DNA as a nutrient. We show here that mutants lacking either ExoI, ExoVII, ExoX, or RecJ are viable during all phases of the bacterial life cycle yet cannot compete with wild-type cells during long-term stationary-phase incubation. We also show that nuclease mutants, alone or in combination, are defective in DNA catabolism, with the exception of the ExoX– single mutant. The ExoX– mutant consumes double-stranded DNA better than wild-type cells, possibly implying the presence of two pathways in E. coli for the processing of ssDNA as it enters the cytoplasm.

* Corresponding author. Mailing address: Molecular and Computational Biology Program, Ray R. Irani Hall-RRI 201, University of Southern California, Los Angeles, CA 90089-2910. Phone: (213) 821-1498. Fax: (213) 740-8631. E-mail: sfinkel{at}usc.edu

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

{dagger} Present address: Division of Pulmonary & Critical Care Medicine, UCLA School of Medicine, Los Angeles, CA 90095-1690.

Journal of Bacteriology, June 2009, p. 3712-3716, Vol. 191, No. 11
0021-9193/09/$08.00+0     doi:10.1128/JB.01678-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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