Legionella pneumophila type II secretome reveals unique exoproteins and a chitinase that promotes bacterial persistence in the lung

Sruti Debroy, Jenny Dao, Maria Söderberg, Ombeline Rossier, Nicholas P. Cianciotto*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

155 Scopus citations


Type II protein secretion is critical for Legionella pneumophila infection of amoebae, macrophages, and mice. Previously, we found several enzymes to be secreted by this (Lsp) secretory pathway. To better define the L. pneumophila type II secretome, a 2D electrophoresis proteomic approach was used to compare proteins in wild-type and type II mutant supernatants. We identified 20 proteins that are type II-dependent, including aminopeptidases, an RNase, and chitinase, as well as proteins with no homology to known proteins. Because a chitinase had not been previously reported in Legionella, we determined that wild type secretes activity against both p-nitrophenyl triacetyl chitotriose and glycol chitin. An lsp mutant had a 70-75% reduction in activity, confirming the type II dependency of the secreted chitinase. Newly constructed chitinase (chiA) mutants also had ≈75% less activity, and reintroduction of chiA restored the mutants to normal levels of activity. Although chiA mutants were not impaired for in vitro intracellular infection, they were defective upon intratracheal inoculation into the lungs of A/J mice, and antibodies against ChiA were detectable in infected animals. In contrast, mutants lacking a secreted phosphatase, protease, or one of several lipolytic enzymes were not defective in vivo. In sum, this study shows that the output of type II secretion is greater in magnitude than previously appreciated and includes previously undescribed proteins. Our data also indicate that an enzyme with chitinase activity can promote infection of a mammalian host.

Original languageEnglish (US)
Pages (from-to)19146-19151
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number50
StatePublished - Dec 12 2006


  • Bacterial protein secretion
  • Bacterial virulence
  • Legionnaires' disease

ASJC Scopus subject areas

  • General


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