Legionella pneumophila NudA Is a Nudix hydrolase and virulence factor

We studied the identity and function of the 528-bp gene immediately upstream of Legionella pneumophila F2310 ptsP (enzyme I(Ntr)). This gene, nudA, encoded for a Nudix hydrolase based on the inferred protein sequence. NudA had hydrolytic activity typical of other Nudix hydrolases, such as Escherichia coli YgdP, in that Ap(n)A's, in particular diadenosine pentaphosphate (Ap(5)A), were the preferred substrates. NudA hydrolyzed Ap(5)A to ATP plus ADP. Both ptsP and nudA were cotranscribed. Bacterial two-hybrid analysis showed no PtsP-NudA interactions. Gene nudA was present in 19 of 20 different L. pneumophila strains tested and in 5 of 10 different Legionella spp. other than L. pneumophila. An in-frame nudA mutation was made in L. pneumophila F2310 to determine the phenotype. The nudA mutant was an auxotroph that grew slowly in liquid and on solid media and had a smaller colony size than its parent. In addition, the mutant was more salt resistant than its parent and grew very poorly at 25 degrees C; all of these characteristics, as well as auxotrophy and slow-growth rate, were reversed by transcomplementation with nudA. The nudA mutant was outcompeted by about fourfold by the parent in competition studies in macrophages; transcomplementation almost completely restored this defect. Competition studies in guinea pigs with L. pneumophila pneumonia showed that the nudA mutant was outcompeted by its parent in both lung and spleen. NudA is of major importance for resisting stress in L. pneumophila and is a virulence factor.