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This study examined the effects of incubation in water and amoeba encystment on<jats:italic>L. pneumophila<\/jats:italic>strain JR32 and null mutants in<jats:italic>dot\/icm<\/jats:italic>genes encoding a type IVB secretion system required for entry, delayed acidification of<jats:italic>L. pneumophila<\/jats:italic>-containing phagosomes, and intracellular multiplication when stationary-phase bacteria infect amoebae and macrophages. Following incubation of stationary-phase cultures in water, mutants in<jats:italic>dotA<\/jats:italic>and<jats:italic>dotB<\/jats:italic>, essential for function of the type IVB secretion system, exhibited entry and delay of phagosome acidification comparable to that of strain JR32. Following encystment in<jats:italic>Acanthamoeba castellanii<\/jats:italic>and reversion of cysts to amoeba trophozoites,<jats:italic>dotA<\/jats:italic>and<jats:italic>dotB<\/jats:italic>mutants exhibited intracellular multiplication in amoebae. The<jats:italic>L. pneumophila<\/jats:italic>Lvh locus, encoding a type IVA secretion system homologous to that in<jats:italic>Agrobacterium tumefaciens<\/jats:italic>, was required for restoration of entry and intracellular multiplication in<jats:italic>dot\/icm<\/jats:italic>mutants following incubation in water and amoeba encystment and was required for delay of phagosome acidification in strain JR32. These data support a model in which the Dot\/Icm type IVB secretion system is conditionally rather than absolutely required for<jats:italic>L. pneumophila<\/jats:italic>virulence-related phenotypes. The data suggest that the Lvh type IVA secretion system, previously thought to be dispensable, is involved in virulence-related phenotypes under conditions mimicking the spread of Legionnaires' disease from environmental niches. Since environmental amoebae are implicated as reservoirs for an increasing number of environmental pathogens and for drug-resistant bacteria, the environmental mimics developed here may be useful in virulence studies of other pathogens.<\/jats:p>","DOI":"10.1128\/iai.00956-06","type":"journal-article","created":{"date-parts":[[2006,11,14]],"date-time":"2006-11-14T02:33:56Z","timestamp":1163471636000},"page":"723-735","update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":65,"title":["Environmental Mimics and the Lvh Type IVA Secretion System Contribute to Virulence-Related Phenotypes of<i>Legionella pneumophila<\/i>"],"prefix":"10.1128","volume":"75","author":[{"given":"Purnima","family":"Bandyopadhyay","sequence":"first","affiliation":[{"name":"Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New 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