Temperature-dependent expression of flagella in Legionella

Ott, Manfred; Messner, Paul; Heesemann, J.; Marre, R.; Hacker, Jörg

doi:10.1099/00221287-137-8-1955

Cited by 59 publications

(48 citation statements)

References 30 publications

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“…A role for environmental temperature in natural L. pneumophila infections has been previously suggested by the fact that they arise after exposure to aerosols from domestic water systems (3,4,22), where the optimal growth temperature of the inoculating dose is unclear. Our data combined with the observation that other genes involved in motility and host cell adherence are expressed optimally at lower temperatures (32,41) suggest that growth of L. pneumophila under these conditions may be relevant to natural infections. Alternatively, these genes may play a role only during infections of environmental hosts, aquatic protozoa.…”

Section: Discussionmentioning

confidence: 83%

“…Our finding that temperature plays a role in the ability of L. pneumophila to infect host cells is consistent with previous observations that temperature regulates the expression of a type IV pilus in L. pneumophila that also plays a role in adherence (27,41). Furthermore, temperature has been shown to play an important role in the regulation of flagellum expression (23,32), and motility has been implicated in the ability of L. pneumophila to infect host cells (12). Three other loci have been identified that play a role in entry by L. pneumophila, but the effects of temperature on their regulation have not been examined (10).…”

Section: Discussionmentioning

confidence: 99%

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Identification of a Gene That Affects the Efficiency of Host Cell Infection by Legionella pneumophila in a Temperature-Dependent Fashion

et al. 2003

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The ability to infect host cells is critical for the survival and replication of intracellular pathogens in humans. We previously found that many genes involved in the ability of Legionella pneumophila to infect macrophages are not expressed efficiently under standard laboratory growth conditions. We have developed an approach using expression of L. pneumophila genes from an exogenous constitutive promoter on a low-copynumber vector that allows identification of genes involved in host cell infection. Through the use of this strategy, we found that expression of a gene, lvhB2, enhances the efficiency of L. pneumophila infection of mammalian cells. The putative protein encoded by lvhB2 has similarity to structural pilin subunits of type IV secretion systems. We confirmed that this gene plays a role in host cell infection by the construction of an in-frame deletion in the L. pneumophila lvhB2 gene and complementation of this mutant with the wild-type gene. The lvhB2 mutant does not display a very obvious defect in interactions with host cells when the bacteria are grown at 37°C, but it has an approximately 100-fold effect on entry and intracellular replication when grown at 30°C. These data suggest that lvhB2 plays an important role in the efficiency of host cell infection by L. pneumophila grown at lower temperatures.Legionella pneumophila, the causative agent of Legionnaires' disease, replicates primarily intracellularly within monocytes during infections in humans and animals (11, 48). Thus, the ability to productively infect monocytic cells is critical to pathogenesis by L. pneumophila. Entry into monocytes can occur via an unusual mechanism termed "coiling phagocytosis," where a filipodium wraps asymmetrically around the bacterium (8,25,33). Conventional phagocytic events are also observed with L. pneumophila (7,25,33); however, coiling phagocytosis correlates with intracellular survival and virulence (7). Although this type of phagocytosis has also been observed in spirochetes, the mechanism by which coiling occurs is not understood (5,34,35,42). In order to better understand the mechanism(s) used by L. pneumophila to productively infect host cells, we set out to identify the bacterial components involved.Since bacteria are efficient organisms, they express only the genes needed to survive and replicate under specific growth conditions (13,28,29). We have recently shown that the frequency of coiling phagocytosis in monocytes increases after intracellular growth in amoebae, suggesting that the genes involved are downregulated on standard laboratory media (7,8). This information has been used to identify L. pneumophila entry loci through overexpression in wild-type bacteria (10). These studies resulted in the identification of three loci, enh1, enh2, and enh3, that play a role in entry by L. pneumophila into host cells. The rtxA and enhC genes, present in the enh1 and enh2 loci, respectively, have been shown to play a role in entry but when mutated only reduce uptake by approximately 50% (10). Despite this rela...

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Section: Discussionmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Identification of a Gene That Affects the Efficiency of Host Cell Infection by Legionella pneumophila in a Temperature-Dependent Fashion

et al. 2003

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“…It also expresses type IV pili, although no form of motility has ever been linked to this organelle in Legionella (70,71,97,113). Flagella and pili are expressed by L. pneumophila grown at 25 to 37°C (71,88,105). Thus, as a first step to understanding the molecular basis for our results, we constructed derivatives of strain 130b that contained a mutation in the gene (flaA) encoding the flagellin subunit (52) ( Table 1).…”

Section: Resultsmentioning

confidence: 99%

Surface Translocation byLegionella pneumophila: a Form of Sliding Motility That Is Dependent upon Type II Protein Secretion

2009

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Legionella pneumophila exhibits surface translocation when it is grown on a buffered charcoal yeast extract (BCYE) containing 0.5 to 1.0% agar. After 7 to 22 days of incubation, spreading legionellae appear in an amorphous, lobed pattern that is most manifest at 25 to 30°C. All nine L. pneumophila strains examined displayed the phenotype. Surface translocation was also exhibited by some, but not all, other Legionella species examined. L. pneumophila mutants that were lacking flagella and/or type IV pili behaved as the wild type did when plated on low-percentage agar, indicating that the surface translocation is not swarming or twitching motility. A translucent film was visible atop the BCYE agar, advancing ahead of the spreading legionellae. Based on its abilities to disperse water droplets and to promote the spreading of heterologous bacteria, the film appeared to manipulate surface tension and, as such, acted like a surfactant. Indeed, a sample obtained from the film rapidly dispersed when it was spotted onto a plastic surface. L. pneumophila type II secretion (Lsp) mutants, but not their complemented derivatives, were defective for both surface translocation and film production. In contrast, mutants defective for type IV secretion exhibited normal surface translocation. When lsp mutants were spotted onto film produced by the wild type, they were able to spread, suggesting that type II secretion promotes the elaboration of the Legionella surfactant. Together, these data indicate that L. pneumophila exhibits a form of surface translocation that is most akin to "sliding motility" and uniquely dependent upon type II secretion.The genus Legionella was established in 1977, following the isolation of Legionella pneumophila from patients with a form of pneumonia now known as Legionnaires' disease (33). Today, L. pneumophila is recognized as a common cause of both community-acquired and nosocomial pneumonia (84). Legionellosis occurs sporadically and in large outbreaks, with the largest outbreak occurring as recently as 2003 and encompassing 800 suspected and 449 confirmed cases (43). L. pneumophila is especially pathogenic for the elderly and the immunocompromised, large and growing segments of the population (39, 84), and recent studies have been highlighting the growing significance of travel-associated Legionnaires' disease (107). L. pneumophila is a gram-negative, gammaproteobacterium that is widespread in natural and manufactured water systems (22,39,93). Infection occurs after the inhalation of Legionellacontaminated water droplets originating from a wide variety of aerosol-generating devices (39). Alarmingly, outbreaks can occur following the airborne spread of L. pneumophila over distances of Ͼ10 km from cooling towers or scrubbers (86). Within its aquatic habitats, L. pneumophila survives over a wide temperature range and grows on surfaces, in biofilms, and as an intracellular parasite of protozoa (9,39,110). Within the mammalian lung, the organism has the ability to attach to and invade macrophages and epit...

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“…Motility-defective bacteria of some species have been reported to be affected in virulence because of aberrations in host cell adherence, invasion mechanisms, or other unknown factors (10,14,35,36). Previous studies utilizing insertional mutagenesis have linked the expression of flagella by L. pneumophila and the ability of this pathogen to infect A. castellanii, H. vermiformis, and human U937 cells (6,38).…”

Section: Discussionmentioning

confidence: 99%

“…Previous reports suggest that the expression of flagella is temperature regulated, since it is repressed at temperatures higher than 37°C (36). Recently, we demonstrated that the expression of the flaA gene is regulated at the transcriptional level (24) by the alternative 28 factor (FliA) and probably by FlaR, a regulator of the LysR family (25).…”

mentioning

confidence: 99%

Flagellum of Legionella pneumophila Positively Affects the Early Phase of Infection of Eukaryotic Host Cells

et al. 2001

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Legionella pneumophila, the etiologic agent of Legionnaires' disease, contains a single, monopolar flagellum which is composed of one major subunit, the FlaA protein. To evaluate the role of the flagellum in the pathogenesis and ecology of Legionella, the flaA gene of L. pneumophila Corby was mutagenized by introduction of a kanamycin resistance cassette. Immunoblots with antiflagellin-specific polyclonal antiserum, electron microscopy, and motility assays confirmed that the specific flagellar mutant L. pneumophila Corby KH3 was nonflagellated. The redelivery of the intact flaA gene into the chromosome (L. pneumophila Corby CD10) completely restored flagellation and motility. Coculture studies showed that the invasion efficiency of the flaA mutant was moderately reduced in amoebae and severely reduced in HL-60 cells. In contrast, adhesion and the intracellular rate of replication remained unaffected. Taking these results together, we have demonstrated that the flagellum of L. pneumophila positively affects the establishment of infection by facilitating the encounter of the host cell as well as by enhancing the invasion capacity.Legionella pneumophila, the etiologic agent of Legionnaires' disease, is a ubiquitous microorganism inhabiting natural and man-made freshwater biotopes (5). In these environments, the gram-negative, rod-shaped bacteria survive as intracellular pathogens of protozoan organisms such as Acanthamoeba castellanii, Hartmannella vermiformis, and Naegleria spp. (15). Upon transmission to individuals via L. pneumophila-containing aerosols generated by showerheads and air-conditioning systems, the bacteria invade and multiply within alveolar macrophages (1, 2, 7) and nonphagocytic cells (17). The infection which mainly affects immunocompromised patients results in a life-threatening atypical pneumonia (7).Detailed ultrastructural and molecular studies of the intracellular fate of the bacterium revealed that human macrophages and protozoan cells infected with L. pneumophila exhibit remarkable similarities concerning the establishment of a replicative phagosome (3,16,22,42,45). However, significant differences were observed during early stages of infection (21). Uptake by Hartmannella is accomplished by a microfilamentindependent mechanism that is sensitive to methylamine, which is an inhibitor of receptor-mediated endocytosis (28). So far, one receptor of Hartmanella vermiformis, a Gal/GalNAc lectin, could be identified (46). Attachment of L. pneumophila to this lectin results in tyrosine dephosphorylation of multiple host cell proteins. However, depending on the type of amoeba, different receptors might be involved (22). In contrast, the uptake by human macrophages occurs following binding of complement receptors CR1 and CR3 via microfilament-dependent phagocytosis (26). In addition to this cytochalasin D-sensitive mechanism, complement-independent mechanisms for uptake by nonphagocytic cells have been described (39).The influence of bacterial motility on infection processes or on survival of legio...

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Temperature-dependent expression of flagella in Legionella

Cited by 59 publications

References 30 publications

Identification of a Gene That Affects the Efficiency of Host Cell Infection by Legionella pneumophila in a Temperature-Dependent Fashion

Identification of a Gene That Affects the Efficiency of Host Cell Infection by Legionella pneumophila in a Temperature-Dependent Fashion

Surface Translocation byLegionella pneumophila: a Form of Sliding Motility That Is Dependent upon Type II Protein Secretion

Flagellum of Legionella pneumophila Positively Affects the Early Phase of Infection of Eukaryotic Host Cells

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