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In vitro secretion kinetics of proteins from Legionella pneumophila in comparison to proteins from non-pneumophila species

Abteilung für Transfusionsmedizin, Universitätsklinikum Tübingen, Otfried-Müller-Str. 4/1, D-72076 Tübingen, Germany¹

Author for correspondence: Birgid Neumeister. Tel: +49 7071 29 81608. Fax: +49 7071 29 5240. e-mail: birgid.neumeister{at}med.uni-tuebingen.de

It has been shown that the loss of PilD, a prepilin peptidase necessary for type IV pilus biogenesis and establishment of the type II secretion apparatus is associated with loss of virulence in Legionella pneumophila. L. pneumophila is the species most frequently associated with Legionnaires’ disease, but virulence factors unique to this species are not known, so the secretion kinetics of several pilD-dependent enzyme activities, including protease, acid phosphatase, phospholipase A (PLA) and lysophospholipase A (LPLA), of L. pneumophila and non-pneumophila species were compared during growth in BYE broth. Enzyme activity appeared during mid-exponential growth phase and reached maximal levels on entry into stationary growth phase. None of the enzyme activities were unique to L. pneumophila and it did not exclusively secrete the highest amounts of the hydrolytic proteins. However, the timing of PLA and LPLA secretion in L. pneumophila differed compared to other species. PLA activity was secreted prior to LPLA activity in L. pneumophila, which may lead to an accumulation of the cytotoxic agent lysophosphatidylcholine (LPC). In addition to L. pneumophila, several other Legionella species, including Legionella steigerwaltii and Legionella gormanii, were able to enrich for LPC due to a very potent PLA activity accompanied by only moderate LPLA activity. These species, in contrast to L. pneumophila, have not been shown to multiply within monocytic host cells. Thus none of the secreted enzymic activities investigated were unique to L. pneumophila, nor were they secreted at high concentrations. However, the timing of PLA and LPLA secretion may contribute to pathogenicity.

Keywords: virulence, exotoxins, intracellular bacteria, phospholipase A, lysophospholipase A

Abbreviations: CS, culture supernatant; DPPC, dipalmitoylphosphatidylcholine; DPPG, dipalmitoylphosphatidylglycerol; FFA, free fatty acid; LPC, lysophosphatidylcholine; LPLA, lysophospholipase A; MPLPC, monopalmitoyllysophosphatidylcholine; PLA, phospholipase A; p-NPP, p-nitrophenylphosphate

This work was in part presented as a poster and published as an abstract at the 5th International Conference on Legionella.

^a Present address: Department of Microbiology-Immunology, NorthWestern University Medical School, 320 E Superior St, Searle 6-541, Chicago, IL 60611, USA.

^b Present address: Department of Microbiology and Immunology, Chandler Medical Center, University of Kentucky, Lexington, KY 40536, USA.

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