Arginine dependency is a therapeutically exploitable vulnerability in chronic myeloid leukaemic stem cells

To fuel accelerated proliferation, leukaemic cells undergo metabolic deregulation, which can result in specific nutrient dependencies. Here, we perform an amino acid drop-out screen and apply pre-clinical models of chronic phase chronic myeloid leukaemia (CML) to identify arginine as a nutrient essential for primary human CML cells. Analysis of the Microarray Innovations in Leukaemia (MILE) dataset uncovers reduced ASS1 levels in CML compared to most other leukaemia types. Stable isotope tracing reveals repressed activity of all urea cycle enzymes in patient-derived CML CD34+ cells, rendering them arginine auxotrophic. Thus, arginine deprivation completely blocks proliferation of CML CD34+ cells and induces significantly higher levels of apoptosis when compared to arginine-deprived cell lines. Similarly, primary CML cells, but not normal CD34+ samples, are particularly sensitive to treatment with the arginine-depleting enzyme, BCT-100, which induces apoptosis and reduces clonogenicity. Moreover, BCT-100 is highly efficacious in a patient-derived xenograft model, causing > 90% reduction in the number of human leukaemic stem cells (LSCs). These findings indicate arginine depletion to be a promising and novel strategy to eradicate therapy resistant LSCs.

Metabolic profiling stratifies colorectal cancer and reveals adenosylhomocysteinase as a therapeutic target

The genomic landscape of colorectal cancer (CRC) is shaped by inactivating mutations in tumour suppressors such as APC, and oncogenic mutations such as mutant KRAS. Here we used genetically engineered mouse models, and multimodal mass spectrometry-based metabolomics to study the impact of common genetic drivers of CRC on the metabolic landscape of the intestine. We show that untargeted metabolic profiling can be applied to stratify intestinal tissues according to underlying genetic alterations, and use mass spectrometry imaging to identify tumour, stromal and normal adjacent tissues. By identifying ions that drive variation between normal and transformed tissues, we found dysregulation of the methionine cycle to be a hallmark of APC-deficient CRC. Loss of Apc in the mouse intestine was found to be sufficient to drive expression of one of its enzymes, adenosylhomocysteinase (AHCY), which was also found to be transcriptionally upregulated in human CRC. Targeting of AHCY function impaired growth of APC-deficient organoids in vitro, and prevented the characteristic hyperproliferative/crypt progenitor phenotype driven by acute deletion of Apc in vivo, even in the context of mutant Kras. Finally, pharmacological inhibition of AHCY reduced intestinal tumour burden in ApcMin/+ mice indicating its potential as a metabolic drug target in CRC.

Absent expansion of AXIN2+ hepatocytes and altered physiology in Axin2CreERT2 mice challenges the role of pericentral hepatocytes in homeostatic liver regeneration

BACKGROUND & AIMS

Mouse models of lineage tracing have helped to describe the important subpopulations of hepatocytes responsible for liver regeneration. However, conflicting results have been obtained from different models. Herein, we aimed to reconcile these conflicting reports by repeating a key lineage-tracing study from pericentral hepatocytes and characterising this Axin2CreERT2 model in detail.

METHODS

We performed detailed characterisation of the labelled population in the Axin2CreERT2 model. We lineage traced this cell population, quantifying the labelled population over 1 year and performed in-depth phenotypic comparisons, including transcriptomics, metabolomics and analysis of proteins through immunohistochemistry, of Axin2CreERT2 mice to WT counterparts.

RESULTS

We found that after careful definition of a baseline population, there are marked differences in labelling between male and female mice. Upon induced lineage tracing there was no expansion of the labelled hepatocyte population in Axin2CreERT2 mice. We found substantial evidence of disrupted homeostasis in Axin2CreERT2 mice. Offspring are born with sub-Mendelian ratios and adult mice have perturbations of hepatic Wnt/β-catenin signalling and related metabolomic disturbance.

CONCLUSIONS

We find no evidence of predominant expansion of the pericentral hepatocyte population during liver homeostatic regeneration. Our data highlight the importance of detailed preclinical model characterisation and the pitfalls which may occur when comparing across sexes and backgrounds of mice and the effects of genetic insertion into native loci.

IMPACT AND IMPLICATIONS

Understanding the source of cells which regenerate the liver is crucial to harness their potential to regrow injured livers. Herein, we show that cells which were previously thought to repopulate the liver play only a limited role in physiological regeneration. Our data helps to reconcile differing conclusions drawn from results from a number of prior studies and highlights methodological challenges which are relevant to preclinical models more generally.

Hepatic glutamine synthetase controls N5-methylglutamine in homeostasis and cancer

Glutamine synthetase (GS) activity is conserved from prokaryotes to humans, where the ATP-dependent production of glutamine from glutamate and ammonia is essential for neurotransmission and ammonia detoxification. Here, we show that mammalian GS uses glutamate and methylamine to produce a methylated glutamine analog, N5-methylglutamine. Untargeted metabolomics revealed that liver-specific GS deletion and its pharmacological inhibition in mice suppress hepatic and circulating levels of N5-methylglutamine. This alternative activity of GS was confirmed in human recombinant enzyme and cells, where a pathogenic mutation in the active site (R324C) promoted the synthesis of N5-methylglutamine over glutamine. N5-methylglutamine is detected in the circulation, and its levels are sustained by the microbiome, as demonstrated by using germ-free mice. Finally, we show that urine levels of N5-methylglutamine correlate with tumor burden and GS expression in a β-catenin-driven model of liver cancer, highlighting the translational potential of this uncharacterized metabolite.

Cyclocreatine Suppresses Creatine Metabolism and Impairs Prostate Cancer Progression

Prostate cancer is the second most common cause of cancer mortality in men worldwide. Applying a novel genetically engineered mouse model (GEMM) of aggressive prostate cancer driven by deficiency of the tumor suppressors PTEN and Sprouty2 (SPRY2), we identified enhanced creatine metabolism as a central component of progressive disease. Creatine treatment was associated with enhanced cellular basal respiration in vitro and increased tumor cell proliferation in vivo. Stable isotope tracing revealed that intracellular levels of creatine in prostate cancer cells are predominantly dictated by exogenous availability rather than by de novo synthesis from arginine. Genetic silencing of creatine transporter SLC6A8 depleted intracellular creatine levels and reduced the colony-forming capacity of human prostate cancer cells. Accordingly, in vitro treatment of prostate cancer cells with cyclocreatine, a creatine analog, dramatically reduced intracellular levels of creatine and its derivatives phosphocreatine and creatinine and suppressed proliferation. Supplementation with cyclocreatine impaired cancer progression in the PTEN- and SPRY2-deficient prostate cancer GEMMs and in a xenograft liver metastasis model. Collectively, these results identify a metabolic vulnerability in prostate cancer and demonstrate a rational therapeutic strategy to exploit this vulnerability to impede tumor progression.

SIGNIFICANCE

Enhanced creatine uptake drives prostate cancer progression and confers a metabolic vulnerability to treatment with the creatine analog cyclocreatine.

The pathogenesis of mesothelioma is driven by a dysregulated translatome

Malignant mesothelioma (MpM) is an aggressive, invariably fatal tumour that is causally linked with asbestos exposure. The disease primarily results from loss of tumour suppressor gene function and there are no 'druggable' driver oncogenes associated with MpM. To identify opportunities for management of this disease we have carried out polysome profiling to define the MpM translatome. We show that in MpM there is a selective increase in the translation of mRNAs encoding proteins required for ribosome assembly and mitochondrial biogenesis. This results in an enhanced rate of mRNA translation, abnormal mitochondrial morphology and oxygen consumption, and a reprogramming of metabolic outputs. These alterations delimit the cellular capacity for protein biosynthesis, accelerate growth and drive disease progression. Importantly, we show that inhibition of mRNA translation, particularly through combined pharmacological targeting of mTORC1 and 2, reverses these changes and inhibits malignant cell growth in vitro and in ex-vivo tumour tissue from patients with end-stage disease. Critically, we show that these pharmacological interventions prolong survival in animal models of asbestos-induced mesothelioma, providing the basis for a targeted, viable therapeutic option for patients with this incurable disease.

MYC regulates fatty acid metabolism through a multigenic program in claudin-low triple negative breast cancer

Background

Recent studies have suggested that fatty acid oxidation (FAO) is a key metabolic pathway for the growth of triple negative breast cancers (TNBCs), particularly those that have high expression of MYC. However, the underlying mechanism by which MYC promotes FAO remains poorly understood.

Methods

We used a combination of metabolomics, transcriptomics, bioinformatics, and microscopy to elucidate a potential mechanism by which MYC regulates FAO in TNBC.

Results

We propose that MYC induces a multigenic program that involves changes in intracellular calcium signalling and fatty acid metabolism. We determined key roles for fatty acid transporters (CD36), lipases (LPL), and kinases (PDGFRB, CAMKK2, and AMPK) that each contribute to promoting FAO in human mammary epithelial cells that express oncogenic levels of MYC. Bioinformatic analysis further showed that this multigenic program is highly expressed and predicts poor survival in the claudin-low molecular subtype of TNBC, but not other subtypes of TNBCs, suggesting that efforts to target FAO in the clinic may best serve claudin-low TNBC patients.

Conclusion

We identified critical pieces of the FAO machinery that have the potential to be targeted for improved treatment of patients with TNBC, especially the claudin-low molecular subtype.

Improving the metabolic fidelity of cancer models with a physiological cell culture medium

Currently available cell culture media may not reproduce the in vivo metabolic environment of tumors. To demonstrate this, we compared the effects of a new physiological medium, Plasmax, with commercial media. We prove that the disproportionate nutrient composition of commercial media imposes metabolic artifacts on cancer cells. Their supraphysiological concentrations of pyruvate stabilize hypoxia-inducible factor 1α in normoxia, thereby inducing a pseudohypoxic transcriptional program. In addition, their arginine concentrations reverse the urea cycle reaction catalyzed by argininosuccinate lyase, an effect not observed in vivo, and prevented by Plasmax in vitro. The capacity of cancer cells to form colonies in commercial media was impaired by lipid peroxidation and ferroptosis and was rescued by selenium present in Plasmax. Last, an untargeted metabolic comparison revealed that breast cancer spheroids grown in Plasmax approximate the metabolic profile of mammary tumors better. In conclusion, a physiological medium improves the metabolic fidelity and biological relevance of in vitro cancer models.

Abstract 1441: MYC expression promotes lipid metabolism and metabolic plasticity in human mammary epithelial cells

MYC is one of the most commonly mutated and highly amplified oncogenes in human breast cancer. MYC amplifications occur most frequently in triple-negative breast cancers (TNBCs). TNBCs can be divided into two molecular subtypes: basal-like and claudin-low breast cancers. These cancers tend to be extremely aggressive and are strongly associated with disease recurrence, poor prognosis and high mortality. In particular, claudin-low tumors are classified by a loss of tight junctions and cell-to-cell contacts and an enrichment for genes associated with an epithelial-to-mesenchymal transition (EMT) and mammary stem cells (also known as tumor-initiating cells). Despite the high level of disease severity, there are no targeted therapies for claudin-low TNBCs. To address this unmet need, we utilized human mammary epithelial cells (HuMECs) that express oncogenic levels of MYC and a mutant MYC (T58A) to characterize the behavioral and metabolic changes that occur during the formation of MYC-driven breast cancers. We found that MYC regulates the expression of genes associated with cell stemness, EMT, lipid metabolism, and calcium (Ca2+) signaling and that the expression of this gene signature promotes cell growth, survival, migration, and metabolic plasticity. The gene signature of MYC-expressing HuMECs highly correlates with the gene signature of claudin-low breast cancers, therefore highlighting the relevance of our HuMEC model to human claudin-low breast cancer. We found the major drivers underlying the MYC-dependent changes in cell behavior to be stimulation of Ca2+ signaling and strong activation of lipid metabolism. Ca2+ signaling is stimulated through the MYC-dependent repression of Ca2+ efflux mechanisms; elevated cytosolic Ca2+ then consequently stimulates a Ca2+/calmodulin kinase kinase 2 (CAMKK2)/AMPK signaling axis that activates fatty acid scavenging and transport, as well as β-oxidation. Enhanced lipid metabolism thereby provides the necessary biomass (fatty acids) for phospholipid biosynthesis and energy (ATP) to support the metabolically demanding processes of cell growth, proliferation, and migration. In all, our findings provide a strong rationale for targeting lipid metabolism and the Ca2+/CAMKK2/AMPK signaling axis in MYC-driven, and potentially claudin-low, breast cancers.

Citation Format: Jessica C. Casciano, Adam Cohen-Nowak, Johan Vande Voorde, Qifeng Zhang, Susan Chalmers, Mairi Sandison, Ann Hedley, Tony McBryan, Thomas Beer, Hsin-Yao Tang, David W. Speicher, Peter Adams, Xiufeng Liu, Richard Schlegel, John McCarron, Michael J. Wakelam, Eyal Gottlieb, Zachary T. Schug. MYC expression promotes lipid metabolism and metabolic plasticity in human mammary epithelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1441.

Increased formate overflow is a hallmark of oxidative cancer

Formate overflow coupled to mitochondrial oxidative metabolism\ has been observed in cancer cell lines, but whether that takes place in the tumor microenvironment is not known. Here we report the observation of serine catabolism to formate in normal murine tissues, with a relative rate correlating with serine levels and the tissue oxidative state. Yet, serine catabolism to formate is increased in the transformed tissue of in vivo models of intestinal adenomas and mammary carcinomas. The increased serine catabolism to formate is associated with increased serum formate levels. Finally, we show that inhibition of formate production by genetic interference reduces cancer cell invasion and this phenotype can be rescued by exogenous formate. We conclude that increased formate overflow is a hallmark of oxidative cancers and that high formate levels promote invasion via a yet unknown mechanism.

Acetate Recapturing by Nuclear Acetyl-CoA Synthetase 2 Prevents Loss of Histone Acetylation during Oxygen and Serum Limitation

Acetyl-CoA is a key metabolic intermediate with an important role in transcriptional regulation. The nuclear-cytosolic acetyl-CoA synthetase 2 (ACSS2) was found to sustain the growth of hypoxic tumor cells. It generates acetyl-CoA from acetate, but exactly which pathways it supports is not fully understood. Here, quantitative analysis of acetate metabolism reveals that ACSS2 fulfills distinct functions depending on its cellular location. Exogenous acetate uptake is controlled by expression of both ACSS2 and the mitochondrial ACSS1, and ACSS2 supports lipogenesis. The mitochondrial and lipogenic demand for two-carbon acetyl units considerably exceeds the uptake of exogenous acetate, leaving it to only sparingly contribute to histone acetylation. Surprisingly, oxygen and serum limitation increase nuclear localization of ACSS2. We find that nuclear ACSS2 recaptures acetate released from histone deacetylation for recycling by histone acetyltransferases. Our work provides evidence for limited equilibration between nuclear and cytosolic acetyl-CoA and demonstrates that ACSS2 retains acetate to maintain histone acetylation.

The metabolic fate of acetate in cancer

Recent high-profile reports have reignited an interest in acetate metabolism in cancer. Acetyl-CoA synthetases that catalyse the conversion of acetate to acetyl-CoA have now been implicated in the growth of hepatocellular carcinoma, glioblastoma, breast cancer and prostate cancer. In this Review, we discuss how acetate functions as a nutritional source for tumours and as a regulator of cancer cell stress, and how preventing its (re)capture by cancer cells may provide an opportunity for therapeutic intervention.

The Nurture of Tumors Can Drive Their Metabolic Phenotype

Many commonly accepted principles in tumor metabolism rely on in vitro studies performed under conditions which cannot faithfully recapitulate tumor heterogeneity. Davidson et al. (2016), in this issue of Cell Metabolism, and Hensley et al. (2016) find that the in vivo environment dictates the metabolic phenotype of lung tumors in patients and mouse models.

Mycoplasma hyorhinis-encoded cytidine deaminase efficiently inactivates cytosine-based anticancer drugs

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Mycoplasmas may colonize tumor tissue in patients.

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Mycoplasma-encoded cytidine deaminase deaminates cytosine-based anticancer drugs.

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The activity of gemcitabine is compromised in mycoplasma-infected tumor cells.

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Gemcitabine activity can be restored by nucleosides or a PNP inhibitor.

Mycoplasmas may colonize tumor tissue in patients. The cytostatic activity of gemcitabine was dramatically decreased in Mycoplasma hyorhinis-infected tumor cell cultures compared with non-infected tumor cell cultures. This mycoplasma-driven drug deamination could be prevented by exogenous administration of the cytidine deaminase (CDA) inhibitor tetrahydrouridine, but also by the natural nucleosides or by a purine nucleoside phosphorylase inhibitor. The M. hyorhinis-encoded CDA_Hyor gene was cloned, expressed as a recombinant protein and purified. CDA_Hyor was found to be more catalytically active than its human equivalent and efficiently deaminates (inactivates) cytosine-based anticancer drugs. CDA_Hyor expression at the tumor site may result in selective drug inactivation and suboptimal therapeutic efficiency.

Mycoplasmas and cancer: focus on nucleoside metabolism

The standard of care for patients suffering cancer often includes treatment with nucleoside analogues (NAs). NAs are internalized by cell-specific nucleobase/nucleoside transporters and, after enzymatic activation (often one or more phosphorylation steps), interfere with cellular nucleo(s)(t)ide metabolism and DNA/RNA synthesis. Therefore, their efficacy is highly dependent on the expression and activity of nucleo(s)(t)ide-metabolizing enzymes, and alterations thereof (e.g. by down/upregulated expression or mutations) may change the susceptibility to NA-based therapy and/or confer drug resistance. Apart from host cell factors, several other variables including microbial presence may determine the metabolome (i.e. metabolite concentrations) of human tissues. Studying the diversity of microorganisms that are associated with the human body has already provided new insights in several diseases (e.g. diabetes and inflammatory bowel disease) and the metabolic exchange between tissues and their specific microbiota was found to affect the bioavailability and toxicity of certain anticancer drugs, including NAs. Several studies report a preferential colonization of tumor tissues with some mycoplasma species (mostly Mycoplasma hyorhinis). These prokaryotes are also a common source of cell culture contamination and alter the cytostatic activity of some NAs in vitro due to the expression of nucleoside-catabolizing enzymes. Mycoplasma infection may therefore bias experimental work with NAs, and their presence in the tumor microenvironment could be of significance when optimizing nucleoside-based cancer treatment.

Nucleoside-catabolizing enzymes in mycoplasma-infected tumor cell cultures compromise the cytostatic activity of the anticancer drug gemcitabine

The intracellular metabolism and cytostatic activity of the anticancer drug gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdC) was severely compromised in Mycoplasma hyorhinis-infected tumor cell cultures. Pronounced deamination of dFdC to its less cytostatic metabolite 2',2'-difluoro-2'-deoxyuridine was observed, both in cell extracts and spent culture medium (i.e. tumor cell-free but mycoplasma-containing) of mycoplasma-infected tumor cells. This indicates that the decreased antiproliferative activity of dFdC in such cells is attributed to a mycoplasma cytidine deaminase causing rapid drug catabolism. Indeed, the cytostatic activity of gemcitabine could be restored by the co-administration of tetrahydrouridine (a potent cytidine deaminase inhibitor). Additionally, mycoplasma-derived pyrimidine nucleoside phosphorylase (PyNP) activity indirectly potentiated deamination of dFdC: the natural pyrimidine nucleosides uridine, 2'-deoxyuridine and thymidine inhibited mycoplasma-associated dFdC deamination but were efficiently catabolized (removed) by mycoplasma PyNP. The markedly lower anabolism and related cytostatic activity of dFdC in mycoplasma-infected tumor cells was therefore also (partially) restored by a specific TP/PyNP inhibitor (TPI), or by exogenous thymidine. Consequently, no effect on the cytostatic activity of dFdC was observed in tumor cell cultures infected with a PyNP-deficient Mycoplasma pneumoniae strain. Because it has been reported that some commensal mycoplasma species (including M. hyorhinis) preferentially colonize tumor tissue in cancer patients, our findings suggest that the presence of mycoplasmas in the tumor microenvironment could be a limiting factor for the anticancer efficiency of dFdC-based chemotherapy. Accordingly, a significantly decreased antitumor effect of dFdC was observed in mice bearing M. hyorhinis-infected murine mammary FM3A tumors compared with uninfected tumors.

Mycoplasma hyorhinis-encoded purine nucleoside phosphorylase: kinetic properties and its effect on the cytostatic potential of purine-based anticancer drugs

A mycoplasma-encoded purine nucleoside phosphorylase (designated PNPHyor) has been cloned and characterized for the first time. Efficient phosphorolysis of natural 6-oxopurine and 6-aminopurine nucleosides was observed, with adenosine the preferred natural substrate (Km = 61 µM). Several cytostatic purine nucleoside analogs proved to be susceptible to PNPHyor-mediated phosphorolysis, and a markedly decreased or increased cytostatic activity was observed in Mycoplasma hyorhinis-infected human breast carcinoma MCF-7 cell cultures (MCF-7.Hyor), depending on the properties of the released purine base. We demonstrated an ∼10-fold loss of cytostatic activity of cladribine in MCF-7.Hyor cells and observed a rapid and complete phosphorolysis of this drug when it was exposed to the supernatant of mycoplasma-infected cells. This conversion (inactivation) could be prevented by a specific PNP inhibitor. These findings correlated well with the high efficiency of PNPHyor-catalyzed phosphorolysis of cladribine to its less toxic base 2-chloroadenine (Km = 80 µM). In contrast, the cytostatic activity of nucleoside analogs carrying a highly toxic purine base and being a substrate for PNPHyor, but not human PNP, was substantially increased in MCF-7.Hyor cells (∼130-fold for fludarabine and ∼45-fold for 6-methylpurine-2'-deoxyriboside). Elimination of the mycoplasma from the tumor cell cultures or selective inhibition of PNPHyor by a PNP inhibitor restored the cytostatic activity of the purine-based nucleoside drugs. Since several studies suggest a high and preferential colonization or association of tumor tissue in cancer patients with different prokaryotes (including mycoplasmas), the data presented here may be of relevance for the optimization of purine nucleoside-based anticancer drug treatment.

Role of human hypoxanthine guanine phosphoribosyltransferase in activation of the antiviral agent T-705 (favipiravir)

6-Fluoro-3-hydroxy-2-pyrazinecarboxamide (T-705) is a novel antiviral compound with broad activity against influenza virus and diverse RNA viruses. Its active metabolite, T-705-ribose-5'-triphosphate (T-705-RTP), is recognized by influenza virus RNA polymerase as a substrate competing with GTP, giving inhibition of viral RNA synthesis and lethal virus mutagenesis. Which enzymes perform the activation of T-705 is unknown. We here demonstrate that human hypoxanthine guanine phosphoribosyltransferase (HGPRT) converts T-705 into its ribose-5'-monophosphate (RMP) prior to formation of T-705-RTP. The anti-influenza virus activity of T-705 and T-1105 (3-hydroxy-2-pyrazinecarboxamide; the analog lacking the 6-fluoro atom) was lost in HGPRT-deficient Madin-Darby canine kidney cells. This HGPRT dependency was confirmed in human embryonic kidney 293T cells undergoing HGPRT-specific gene knockdown followed by influenza virus ribonucleoprotein reconstitution. Knockdown for adenine phosphoribosyltransferase (APRT) or nicotinamide phosphoribosyltransferase did not change the antiviral activity of T-705 and T-1105. Enzymatic assays showed that T-705 and T-1105 are poor substrates for human HGPRT having Km(app) values of 6.4 and 4.1 mM, respectively. Formation of the RMP metabolites by APRT was negligible, and so was the formation of the ribosylated metabolites by human purine nucleoside phosphorylase. Phosphoribosylation and antiviral activity of the 2-pyrazinecarboxamide derivatives was shown to require the presence of the 3-hydroxyl but not the 6-fluoro substituent. The crystal structure of T-705-RMP in complex with human HGPRT showed how this compound binds in the active site. Since conversion of T-705 by HGPRT appears to be inefficient, T-705-RMP prodrugs may be designed to increase the antiviral potency of this new antiviral agent.

Evidence for the presence of Legionella bacteriophages in environmental water samples

The existence and preliminary characterization of bacteriophages active against the Gram-negative human pathogen Legionella pneumophila, the causative agent of a very severe form of pneumonia, are reported. Four phages belonging to the family of the Myoviridae were isolated from various fresh water environments, and preliminary characterization showed that these crude preparations infect exclusively bacteria belonging to the genus Legionella. Standard phage amplification, purification, and characterization procedures were, however, not efficiently applicable making more research into these novel phages and their mechanism of infection necessary. The existence of Legionella bacteriophages is very promising for future applications such as the development of novel molecular tools, the design of new detection and typing methods, and the bioremediation of this environmental pathogen.