Legionella pneumophila (Lpn) is a ubiquitous Gram-negative bacterium in aquatic systems and an opportunistic intracellular pathogen in immunocompromised humans causing a severe pneumonia known as Legionnaires’ disease. Using a mouse model, we investigated molecular and cellular players in the innate immune response to infection with Lpn. We observed robust levels of inflammatory cytokines in the serum upon intranasal or i.v. infection with live, virulent Lpn, but not with inactivated or avirulent bacteria lacking the Icm/Dot type IV secretion system. Interestingly, Lpn-induced serum cytokines were readily detectable regardless of the capacity of Icm/Dot-proficient Lpn to replicate in host cells and the Lpn permissiveness of the host mice. We found NK cell-derived IFN-γ to be the key cytokine in the resolution of Lpn infection, whereas type I IFNs did not appear to play a major role in our model. Accordingly, NK cell-depleted or IFN-II-R-deficient mice carried severely increased bacterial burdens or failed to control Lpn infection, respectively. Besides the dependence of inflammatory cytokine induction on Lpn virulence, we also demonstrate a strict requirement of MyD88 for this process, suggesting the involvement of TLRs in the recognition of Lpn. However, screening of several TLR-deficient hosts did not reveal a master TLR responsible for the sensing of an Lpn infection, but provided evidence for either redundancy of individual TLRs in Lpn recognition or TLR-independent induction of inflammatory responses.

Legionella pneumophila is a bacterial parasite of freshwater amoebae which also grows in alveolar macrophages and thus causes the potentially fatal pneumonia Legionnaires' disease. Intracellular growth within amoebae and macrophages is mechanistically similar and requires the Icm/Dot type IV secretion system. This paper reports the development of an assay, the amoebae plate test (APT), to analyse growth of L. pneumophila wild-type and icm/dot mutant strains spotted on agar plates in the presence of Acanthamoeba castellanii. In the APT, wild-type L. pneumophila formed robust colonies even at high dilutions, icmT, -R, -P or dotB mutants failed to grow, and icmS or -G mutants were partially growth defective. The icmS or icmG mutant strains were used to screen an L. pneumophila chromosomal library for genes that suppress the growth defect in the presence of the amoebae. An icmS suppressor plasmid was isolated that harboured the icmS and flanking icm genes, indicating that this plasmid complements the intracellular growth defect of the mutant. In contrast, different icmG suppressor plasmids rendered the icmG mutant more cytotoxic for A. castellanii without enhancing intracellular multiplication in amoebae or RAW264.7 macrophages. Deletion of individual genes in the suppressor plasmids inserts identified lcs (Legionella cytotoxic suppressor) -A, -B, -C and -D as being required for enhanced cytotoxicity of an icmG mutant strain. The corresponding proteins show sequence similarity to hydrolases, NlpD-related metalloproteases, lipid A disaccharide synthases and ABC transporters, respectively. Overexpression of LcsC, a putative paralogue of the lipid A disaccharide synthase LpxB, increased cytotoxicity of an icmG mutant but not that of other icm/dot or rpoS mutant strains against A. castellanii. Based on sequence comparison and chromosomal location, lcsB and lcsC probably encode enzymes involved in cell wall maintenance and peptidoglycan metabolism. The APT established here may prove useful to identify other bacterial factors relevant for interactions with amoeba hosts.

Legionella pneumophila is an opportunistic pathogen that in the environment colonizes biofilms and replicates within amoebae. The bacteria employ the intracellular multiplication/defective organelle trafficking (Icm/Dot) type IV secretion system to grow intracellularly in a specific vacuole. Using Acanthamoeba castellanii as a host cell, we have previously identified lcsC (Legionella cytotoxic suppressor), a paralogue of the lipid A disaccharide synthase lpxB, as a cytotoxic factor of L. pneumophila. A bioinformatic analysis of the genome revealed that L. pneumophila is unique in harbouring two paralogues of lpxB and two and three paralogues of the lipid A biosynthesis acyltransferases lpxA and lpxD, respectively. LcsC (lpxB1) forms a transcriptional unit with gnnA, encoding a putative UDP-GlcNAc oxidase in the biosynthetic pathway leading to 3-aminoglucosamine analogues of lipid A. LpxB2 clusters with lpxD2, lpxA2 and lpxL paralogues, encoding secondary acyltransferases. LcsC/lpxB1 and lpxB2 were found to partially complement the growth defect of an Escherichia coli lpxB conditional mutant strain, indicating that both corresponding enzymes possess lipid A disaccharide synthase activity. The two L. pneumophila lpxB paralogues are not functionally equivalent, since expression of lcsC/lpxB1 but not lpxB2 in an L. pneumophila icmG mutant is cytotoxic for A. castellanii, and LPS purified from the two strains triggers CD14-dependent tumour necrosis factor (TNF)a production by macrophages with a different potency. The lpxB and lpxA paralogues are expressed under various growth conditions, including broth, biofilms and in A. castellanii. While the flagellar gene flaA is mainly expressed in late stationary phase, the lpxB and lpxA paralogues are preferentially expressed in the exponential and early stationary phases. Upon exposure to hypotonic stress and nutrient deprivation, lpxA1, and to a lesser extent lcsC/lpxB1, is upregulated. The differential regulation of lpxB or lpxA paralogues in response to changing environmental conditions might allow L. pneumophila to adapt its lipid A structure.Abbreviations: ACES, N-(2-acetamido)-2-aminoethanesulfonic acid; ACP, acyl carrier protein; Icm/Dot, intracellular multiplication/defective organelle trafficking; GlcN, 2-amino-2,3-dideoxy-a-D-glucopyranose (glucosamine); GlcN3N, 2,3-diamino-2,3-dideoxy-a-D-glucopyranose; GlcNAc, ; 2-acetamido-2,3-dideoxy-a-D-glucopyranose (N-acetylglucosamine); GlcNAc3N, 2-acetamido-3-amino-2,3-dideoxy-a-D-glucopyranose; Kdo, 3-deoxy-D-manno-oct-2-ulosonic acid; lcs, Legionella cytotoxic suppressor; PI, propidium iodide; TNF, tumour necrosis factor. 3These authors contributed equally to this work.Supplementary tables listing bacterial strains and plasmids, oligonucleotides used in this study, paralogues of LpxA-C in different bacteria and genomic arrangements of selected lipid A biosynthesis genes in three L. pneumophila strains, and a supplementary figure showing cotranscription of lcsC/lpxB1 and gnnA, are available with the online version of this...

An on-line high-pressure liquid chromatography (HPLC) system capable of measuring amino acids and carbohydrates was used to study metabolism in mammalian cell culture systems. The HPLC method utilized anion-exchange chromatography followed by integrated pulsed amperometric detection. The method is capable of measuring 19 amino acids plus glucose with a complete method time of 65 min. In actual cell cultures, the method was shown to be useful for monitoring 17 amino acids plus glucose. The two amino acids that were not accurately monitored were arginine and lysine, possibly due to their elution near the void volume of the column. The HPLC system was used to study variability in metabolism across different cell culture processes, as well as the effect of glucose and glutamine limitation on a single cell culture process. Chemometric analysis was used to draw statistically meaningful conclusions from the highly correlated, multivariate data set that resulted from these experiments. Using chemometrics, variation between processes was linked to differences in uptake rates of seven amino acids. Similarly, lactate concentration, cell density, and aspartate uptake rate were linked to glucose and glutamine limitation. The effect of nutrient limitation on glutamate, alanine, and ammonium was also considered.

An on-line high-pressure liquid chromatography (HPLC) system capable of measuring amino acids and carbohydrates was used to study metabolism in mammalian cell culture systems. The HPLC method utilized anion-exchange chromatography followed by integrated pulsed amperometric detection. The method is capable of measuring 19 amino acids plus glucose with a complete method time of 65 min. In actual cell cultures, the method was shown to be useful for monitoring 17 amino acids plus glucose. The two amino acids that were not accurately monitored were arginine and lysine, possibly due to their elution near the void volume of the column. The HPLC system was used to study variability in metabolism across different cell culture processes, as well as the effect of glucose and glutamine limitation on a single cell culture process. Chemometric analysis was used to draw statistically meaningful conclusions from the highly correlated, multivariate data set that resulted from these experiments. Using chemometrics, variation between processes was linked to differences in uptake rates of seven amino acids. Similarly, lactate concentration, cell density, and aspartate uptake rate were linked to glucose and glutamine limitation. The effect of nutrient limitation on glutamate, alanine, and ammonium was also considered.