Mr. Liles et al., IDENTIFICATION AND TEMPERATURE REGULATION OF LEGIONELLA-PNEUMOPHILA GENES INVOLVED IN TYPE-IV PILUS BIOGENESIS AND TYPE-II PROTEIN SECRETION, Infection and immunity, 66(4), 1998, pp. 1776-1782
Previously, we had isolated by transposon mutagenesis a Legionella pne
umophila mutant that appeared defective for intracellular iron acquisi
tion. While sequencing in the proximity of the mini-Tn10 insertion, we
found a locus that had a predicted protein product with strong simila
rity to PilB from Pseudomonas aeruginosa. PIE is a component of the ty
pe II secretory pathway, which is required for the assembly of type IV
pill. Consequently, the locus was cloned and sequenced. Within this 4
-kb region were three genes that appeared to be organized in an operon
and encoded homologs of P. aeruginosa PilB, PilC, and PilD, proteins
essential for pilus production and type II protein secretion. Northern
blot analysis identified a transcript large enough to include all thr
ee genes and showed a substantial increase in expression of this opero
n when L. pneumophila was grown at 30 degrees C as opposed to 37 degre
es C. The latter observation was then correlated with an increase in p
iliation when bacteria were grown at the lower temperature. Southern h
ybridization analysis indicated that the pilB locus was conserved with
in L. pneumophila serogroups and other Legionella species. These data
represent the first isolation of type II secretory genes from an intra
cellular parasite and indicate that the legionellae express temperatur
e-regulated type IV pili.