A two-component regulator induces the transmission phenotype of stationary-phase Legionella pneumophila

Pathogenic Legionella pneumophila evolved as a parasite of aquatic amoebae. To persist in the environment, the microbe must be proficient at both replication and transmission. In laboratory cultures, as nutrients become scarce a stringent response-like pathway coordinates exit from the exponential growth phase with induction of traits correlated with virulence, including motility. A screen for mutants that express the flagellin gene poorly identified five activators of virulence: LetA/LetS, a two-component regulator homologous to GacA/GacS of Pseudomonas and SirA/BarA of Salmonella ; the stationary-phase sigma factor RpoS; the flagellar sigma factor FliA; and a new locus, letE . Unlike wild type, post-exponential-phase letA and letS mutants were not motile, cytotoxic, sodium sensitive or proficient at infecting macrophages. L. pneumophila also required fliA to become motile, cytotoxic and to infect macrophages efficiently and letE to express sodium sensitivity and maximal motility and cytotoxicity. When induced to express RelA, all of the strains exited the exponential phase, but only wild type converted to the fully virulent form. In contrast, intracellular replication was independent of letA, letS, letE or fliA . Together, the data indicate that, as the nutrient supply wanes, ppGpp triggers a regulatory cascade mediated by LetA/ LetS, RpoS, FliA and letE that coordinates differentiation of replicating L. pneumophila to a transmissible form.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75531/1/j.1365-2958.2002.02884.x.pd

Variable genetic element typing: A quick method for epidemiological subtyping of Legionella pneumophila

A total of 57 isolates of Legionella pneumophila were randomly selected from the German National Legionella strain collection and typed by monoclonal antibody subgrouping, seven-gene locus sequence-based typing (SBT) scheme and a newly developed variable element typing (VET) system based on the presence or absence of ten variable genetic elements. These elements were detected while screening a genomic library of strain Corby, as well as being taken from published data for PAI-1 (pathogenicity island) from strain Philadelphia. Specific primers were designed and used in gel-based polymerase chain reaction (PCR) assays. PCR amplification of the mip gene served as a control. The end-point was the presence/absence of a PCR product on an ethidium bromide-strained gel. In the present study, the index of discrimination was somewhat lower than that of the SBT (0.87 versus 0.97). Nevertheless, the results obtained showed as a 'proof of principle' that this simple and quick typing assay might be useful for the epidemiological characterisation of L. pneumophila strains

A structural comparison of lipopolysaccharide biosynthesis loci of Legionella pneumophila serogroup 1 strains.

Contains fulltext : 125188.pdf (publisher's version ) (Open Access

Cloning and characterization of a gene (mspA) encoding the major sheath protein Treponema maltophilum ATCC51939(T)

The major sheath protein-encoding gene (mspA) of the oral spirochete Treponema maltophilum ATCC 51939(T) was cloned by screening a genomic library with an anti-outer membrane fraction antibody. The mspA gene encodes a precursor protein of 575 amino acids with a predicted molecular mass of 62.3 kDa, including a signal peptide of 19 amino acids. The native MspA formed a heat-modifiable, detergent- and trypsin-stable complex which is associated with the outer membrane. Hybridization with an mspA-specific probe showed no cross-reactivity with the msp gene from Treponema denticola

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

In Legionella pneumophila, the regulation of the flagellum and the expression of virulence traits are linked. FleQ, RpoN and FliA are the major regulators of the flagellar regulon. We demonstrated here that all three regulatory proteins mentioned (FleQ, RpoN and FliA) are necessary for full in vivo fitness of L. pneumophila strains Corby and Paris. In this study, we clarified the role of FleQ for fliA expression from the level of mRNA toward protein translation. FleQ enhanced fliA expression, but FleQ and RpoN were not necessary for basal expression. In addition, we identified the initiation site of fliA in L. pneumophila and found a putative σ(70) promoter element localized upstream. The initiation site was not influenced in the ΔfleQ or ΔrpoN mutant strain. We demonstrated that there is no significant difference in the regulation of fliA between strains Corby and Paris, but the FleQ-dependent induction of fliA transcription in the exponential phase is stronger in strain Paris than in strain Corby. In addition, we showed for the first time the presence of a straight hook at the pole of the non-flagellated ΔfliA and ΔfliD mutant strains by electron microscopy, indicating the presence of an intact basal body in these strains

Traits of tidal marsh plants determine survival and growth response to hydrodynamic forcing: implications for nature-based shoreline protection

Tidal marshes are increasingly valued for their nature-based shoreline protection function, as they reduce waves, currents and erosion. The effectiveness of this function depends on the ability of tidal marsh plants to grow and survive under pressure from waves and currents. However, how this varies with species-dependent plant traits is poorly understood. We performed a field transplantation experiment to quantify species-specific growth responses to different levels of hydrodynamic exposure and tidal inundation for 3 NW European marsh species: Schoenoplectus tabernaemontani, Bolboschoenus maritimus and Phragmites australis. In this order, these species showed increasing shoot stiffness, length and biomass, which are traits that increase hydrodynamic drag forces experienced by plants. Increased exposure to tidal inundation and hydrodynamics reduced the growth of all 3 species, but species with lower biomass and shorter, thinner and more flexible shoots could better cope with higher hydrodynamic exposure and tidal inundation. Furthermore, transplants of S. tabernaemontani (i.e. the species with the lowest shoot stiffness, length and biomass that survived under all tested conditions) developed smaller, thinner and more flexible shoots in response to higher hydrodynamic exposure and inundation. Hence our study indicates that similar inter- and intra-specific plant traits drive plant growth in response to hydrodynamics and inundation. This suggests that the spatial distribution of species typically observed in tidal marshes results not only from species-specific tolerance to tidal inundation gradients but also from hydrodynamic gradients. Allowing enough space for development of species zonation may be important to increase the efficiency of nature-based shoreline protection by tidal marshes