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Journal of Bacteriology, September 2009, p. 5428-5440, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00477-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Autolysin LytA Contributes to Efficient Bacteriophage Progeny Release in Streptococcus pneumoniae{triangledown}

Maria João Frias, José Melo-Cristino, and Mário Ramirez*

Unidade de Microbiologia Molecular e Infecção, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisbon, Portugal

Received 8 April 2009/ Accepted 23 June 2009

Most bacteriophages (phages) release their progeny through the action of holins that form lesions in the cytoplasmic membrane and lysins that degrade the bacterial peptidoglycan. Although the function of each protein is well established in phages infecting Streptococcus pneumoniae, the role—if any—of the powerful bacterial autolysin LytA in virion release is currently unknown. In this study, deletions of the bacterial and phage lysins were done in lysogenic S. pneumoniae strains, allowing the evaluation of the contribution of each lytic enzyme to phage release through the monitoring of bacterial-culture lysis and phage plaque assays. In addition, we assessed membrane integrity during phage-mediated lysis using flow cytometry to evaluate the regulatory role of holins over the lytic activities. Our data show that LytA is activated at the end of the lytic cycle and that its triggering results from holin-induced membrane permeabilization. In the absence of phage lysin, LytA is able to mediate bacterial lysis and phage release, although exclusive dependence on the autolysin results in reduced virion egress and altered kinetics that may impair phage fitness. Under normal conditions, activation of bacterial LytA, together with the phage lysin, leads to greater phage progeny release. Our findings demonstrate that S. pneumoniae phages use the ubiquitous host autolysin to accomplish an optimal phage exiting strategy.

* Corresponding author. Mailing address: Instituto de Microbiologia, Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Av. Prof. Egas Moniz, 1649-028 Lisbon, Portugal. Phone: 351 217999458. Fax: 351 217999459. E-mail: ramirez{at}fm.ul.pt

{triangledown} Published ahead of print on 6 July 2009.

Journal of Bacteriology, September 2009, p. 5428-5440, Vol. 191, No. 17
0021-9193/09/$08.00+0     doi:10.1128/JB.00477-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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