Implication of the VirD4 Coupling Protein of the Lvh Type 4 Secretion System in Virulence Phenotypes of Legionella pneumophila

Abstract

The genome of the Philadelphia-1 strain of Legionella pneumophila, the causative organism of Legionnaires' disease, encodes two virulence-associated type 4 secretion systems (T4SSs), the Dot/Icm type 4B (T4BSS) and the Lvh type 4A (T4ASS). Broth stationary-phase cultures of most dot/icm mutants are defective in entry and evasion of phagosome acidification. However, those virulence defects can be reversed by incubating broth cultures of dot/icm mutants in water, termed water stress (WS). WS reversal requires the lvh T4ASS locus, suggesting an interaction between the two T4SSs in producing Legionella virulence phenotypes. In the current work, the loss of WS reversal in a dotA ⌬lvh mutant of strain JR32 was shown to be attributable to loss of the lvh virD4 gene, encoding the putative coupling protein of the T4ASS. Transformation of a dotA ⌬lvh mutant with virD4 also reversed entry and phagosome acidification defects in broth cultures. In addition, broth cultures of ⌬lvh and ⌬virD4 mutants, which were dot/icm ؉ , showed 5-fold and >6-fold increases in translocation of the Dot/Icm translocation substrates, proteins RalF and SidD, respectively. These data demonstrate that the Lvh T4ASS functions in both broth stationary-phase cultures conventionally used for infection and cultures exposed to WS treatment. Our studies in a dotA ⌬lvh mutant and in a dot/icm ؉ background establish that VirD4 and the Lvh T4ASS contribute to virulence phenotypes and are consistent with independent functioning of Dot/Icm and Lvh T4SSs or functional substitution of the Lvh VirD4 protein for a component(s) of the Dot/Icm T4BSS.

Genome Sequencing Links Persistent Outbreak of Legionellosis in Sydney (New South Wales, Australia) to an Emerging Clone of Legionella pneumophila Sequence Type 211

“…Unique T4ASS have been found in previous outbreak isolates (17), including from a recent outbreak in western Canada, which is unique in its dry cold conditions that were initially thought to be too harsh for the survival of L. pneumophila (19). The element described in this study contained genes homologous to the Lvh region of other L. pneumophila strains, and genes from this region are thought to assist in intracellular replication (28,29). T4ASS-Sydney was found in only one copy, adjacent to another T4ASS with high homology to that described in L. pneumophila strain Philadelphia (30).…”

The pleiotropic Legionella transcription factor LvbR links the Lqs and c‐di‐GMP regulatory networks to control biofilm architecture and virulence

“…B). This suggests that LvbR and especially LqsR are transcriptional activators for the lvh region, which is involved in virulence (Bandyopadhyay et al ., ). Furthermore, the transcription of flagellum components was dependent on LvbR and LqsR.…”

Functional Type 1 Secretion System Involved in Legionella pneumophila Virulence

“…In L. pneumophila, two secretion systems have been clearly identified (T4ASS Icm/Dot and T2SS Lsp), and their role in the virulence of this bacterium has been extensively studied over the years. Recently, the possibility that the T4BSS Lvh VirD4 protein complements the defect in virulence of a T4ASS-invalidated ⌬dotA mutant was reported (11,37). Genome sequencing data also predicted the existence of a putative autotransporter (T5aSS) in strain Paris (38).…”

“…Bacterial protein secretion systems have been extensively studied, and to date, seven of them have been identified within two categories: those that address their substrates to the extracellular environment, such as type I secretion systems (T1SSs), T2SSs, T5SSs, and T7SSs, and those whose substrates are injected through the host membrane into its cytoplasm, such as T3SSs, T4SSs, and T5SSs (6). In L. pneumophila, a T2SS and a T4SS were identified several years ago (7)(8)(9) and their implication in the virulence of this bacterium has been extensively studied (10,11). T4SS Dot/Icm has been particularly well investigated, as it is responsible for the translocation of more than 275 effector proteins into the cytoplasm of infected cells (12,13).…”