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

It has been shown that the loss of MID, a prepilin peptidase necessary for type IV pilus biogenesis and establishment of the type [I secretion apparat us is associated with loss of virulence in Legionella pneumophila. L. pneum ophila is the species most frequently associated with Legionnaires' disease , but virulence factors unique to this species are not known, so the secret ion kinetics of several pilD-dependent enzyme activities, including proteas e, acid phosphatase, phospholipase A (PLA) and lysophospholipase A (LPLA), of L. pneumophila and non-pneumophila species were compared during growth i n BYE broth. Enzyme activity appeared during mid-exponential growth phase a nd reached maximal levels on entry into stationary growth phase. None of th e enzyme activities were unique to L. pneumophila and it did not exclusivel y secrete the highest amounts of the hydrolytic proteins. However, the timi ng of PLA and LPLA secretion in L. pneumophila differed compared to other s pecies. PLA activity was secreted prior to LPLA activity in L. pneumophila, which may lead to an accumulation of the cytotoxic agent lysophosphatidylc holine (LPC). In addition to L. pneumophila, several other Legionella speci es, including Legionella steigerwaltii and Legionella gormanii, were able t o enrich for LPC due to a very potent PLA activity accompanied by only mode rate LPLA activity. These species, in contrast to L. pneumophila, have not been shown to multiply within monocytic host cells. Thus none of the secret ed enzymic activities investigated were unique to L. pneumophila, nor were they secreted at high concentrations. However, the timing of PLA and LPLA s ecretion may contribute to pathogenicity.