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Journal of Bacteriology, March 2009, p. 1537-1546, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01531-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Surface Translocation by Legionella pneumophila: a Form of Sliding Motility That Is Dependent upon Type II Protein Secretion {triangledown}

Catherine R. Stewart, Ombeline Rossier, and Nicholas P. Cianciotto*

Department of Microbiology and Immunology, Northwestern University Medical School, Chicago, Illinois 60611

Received 29 October 2008/ Accepted 18 December 2008

Legionella pneumophila exhibits surface translocation when it is grown on a buffered charcoal yeast extract (BCYE) containing 0.5 to 1.0% agar. After 7 to 22 days of incubation, spreading legionellae appear in an amorphous, lobed pattern that is most manifest at 25 to 30°C. All nine L. pneumophila strains examined displayed the phenotype. Surface translocation was also exhibited by some, but not all, other Legionella species examined. L. pneumophila mutants that were lacking flagella and/or type IV pili behaved as the wild type did when plated on low-percentage agar, indicating that the surface translocation is not swarming or twitching motility. A translucent film was visible atop the BCYE agar, advancing ahead of the spreading legionellae. Based on its abilities to disperse water droplets and to promote the spreading of heterologous bacteria, the film appeared to manipulate surface tension and, as such, acted like a surfactant. Indeed, a sample obtained from the film rapidly dispersed when it was spotted onto a plastic surface. L. pneumophila type II secretion (Lsp) mutants, but not their complemented derivatives, were defective for both surface translocation and film production. In contrast, mutants defective for type IV secretion exhibited normal surface translocation. When lsp mutants were spotted onto film produced by the wild type, they were able to spread, suggesting that type II secretion promotes the elaboration of the Legionella surfactant. Together, these data indicate that L. pneumophila exhibits a form of surface translocation that is most akin to "sliding motility" and uniquely dependent upon type II secretion.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Northwestern University Medical School, 320 East Superior St., Chicago, IL 60611. Phone: (312) 503-0385. Fax: (312) 503-1339. E-mail: n-cianciotto{at}northwestern.edu

{triangledown} Published ahead of print on 29 December 2008.

Journal of Bacteriology, March 2009, p. 1537-1546, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01531-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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