Characterization of Rosculus vilicus sp. nov., a rhizarian amoeba interacting with Mycobacterium avium subsp. paratuberculosis

Free-living amoebae are described as potential reservoirs for pathogenic bacteria in the environment. It has been hypothesized that this might be the case for Mycobacterium avium subsp. paratuberculosis, the bacterium responsible for paratuberculosis. In a previous work, we isolated an amoeba from a water sample in the environment of infected cattle and showed that this amoeba was associated with Mycobacterium avium subsp. paratuberculosis. While a partial 18S rRNA gene has allowed us to suggest that this amoeba was Rosculus-like, at that time we were not able to sub-cultivate it. In the present study, we succeeded in cultivating this strain at 20-25°C. This amoeba is among the smallest (5-7 μm) described. The sequencing of the whole genome allowed us to extract the full 18S rRNA gene and propose this strain as a new species of the Rosculus genus, i.e., R. vilicus. Of note, the mitochondrial genome is particularly large (184,954 bp). Finally, we showed that this amoeba was able to phagocyte Mycobacterium avium subsp. paratuberculosis and that the bacterium was still observed within amoebae after at least 3 days. In conclusion, we characterized a new environmental amoeba species at the cellular and genome level that was able to interact with Mycobacterium avium subsp. paratuberculosis. As a result, R. vilicus is a potential candidate as environmental reservoir for Mycobacterium avium subsp. paratuberculosis but further experiments are needed to test this hypothesis.

Presence of Non-Tuberculous Mycobacteria Including Mycobacterium avium subsp. paratuberculosis Associated with Environmental Amoebae

One of the obstacles to eradicating paratuberculosis or Johne's Disease (JD) seems to be the persistence of Mycobacterium avium subsp. paratuberculosis (Map) in the environment due to its ability to survive alone or vectorized. It has been shown that Map is widely distributed in soils and water. Previously, we isolated amoebae associated with Map strains in the environment of bovines from an infected herd. This work aims to verify our working hypothesis, which suggests that amoebae may play a role in the transmission of JD. In this study, we sampled water in the vicinity of herds infected with Map or Mycobacterium bovis (M. bovis) and searched for amoebae and mycobacteria. Live amoebae were recovered from all samples. Among these amoebae, four isolates associated with the presence of mycobacteria were identified and characterized. Map and other mycobacterial species were detected by qPCR and, in some cases, by culture. This study suggests that amoebae and Map may be found in the same environment and might represent a risk of exposure of animals to pathogenic mycobacteria. These data open up new perspectives on the control measures to be put in place to prevent contamination by Map.

Here, there and everywhere: Ecology and biology of the Dependentiae phylum

Our view of bacterial diversity has been dramatically impacted by cultivation-independent approaches such as metagenomics and 16S rRNA gene sequencing. Consequently, most bacterial phyla known to date are only documented by the presence of DNA sequences in databases and lack cultivated representatives. This bacterial majority that is yet-to-be cultivated, is forming the 'Microbial Dark Matter', (MDM) a consortium, whose ecology and biology remain largely unexplored. The Candidatus Dependentiae stands as one of many phyla within this MDM, found worldwide in various environments. Genomic evidence suggests ancestral, unusual adaptations of all Ca. Dependentiae to a host dependent lifestyle. In line with this, protists appear to be important for Ca. Dependentiae biology, as revealed by few recent studies, which enabled their growth in laboratory through host cultivation. However, the Ca. Dependentiae still remain to this day a poorly documented phylum. The present review aims to summarize the current knowledge accumulated on this often found, but rarely highlighted, bacterial phylum.

Proteomic analysis of Acanthamoeba castellanii response to Legionella pneumophila infection

Legionella pneumophila is an opportunistic pathogen responsible for Legionnaires' disease or Legionellosis. This bacterium is found in the environment interacting with free-living amoebae such as Acanthamoeba castellanii. Until now, proteomic analyses have been done in amoebae infected with L. pneumophila but focused on the Legionella-containing vacuole. In this study, we propose a global proteomic analysis of the A. castellanii proteome following infection with L. pneumophila wild-type (WT) or with an isogenic ΔdotA mutant strain, which is unable to replicate intracellularly. We found that infection with L. pneumophila WT leads to reduced levels of A. castellanii proteins associated with lipid homeostasis/metabolism, GTPase regulation, and kinase. The levels of organelle-associated proteins were also decreased during infection. Legionellapneumophila WT infection leads to increased levels of proteins associated with polyubiquitination, folding or degradation, and antioxidant activities. This study reinforces our knowledge of this too little explored but so fundamental interaction between L. pneumophila and A. castellanii, to understand how the bacterium could resist amoeba digestion.

Identifying group-specific primers for environmental Heterolobosa by high-throughput sequencing

Diversity of Heterolobosea (Excavata) in environments is poorly understood despite their ecological occurrence and health‐associated risk, partly because this group tends to be under‐covered by most universal eukaryotic primers used for sequencing. To overcome the limits of the traditional morpho‐taxonomy‐based biomonitoring, we constructed a primer database listing existing and newly designed specific primer pairs that have been evaluated for Heterolobosea 18S rRNA sequencing. In silico taxonomy performance against the current SILVA SSU database allowed the selection of primer pairs that were next evaluated on reference culture amoebal strains. Two primer pairs were retained for monitoring the diversity of Heterolobosea in freshwater environments, using high‐throughput sequencing. Results showed that one of the newly designed primer pairs allowed species‐level identification of most heterolobosean sequences. Such primer pair could enable informative, cultivation‐free assays for characterizing heterolobosean populations in various environments.

Delayed cytokinesis generates multinuclearity and potential advantages in the amoeba Acanthamoeba castellanii Neff strain

Multinuclearity is a widespread phenomenon across the living world, yet how it is achieved, and the potential related advantages, are not systematically understood. In this study, we investigate multinuclearity in amoebae. We observe that non-adherent amoebae are giant multinucleate cells compared to adherent ones. The cells solve their multinuclearity by a stretchy cytokinesis process with cytosolic bridge formation when adherence resumes. After initial adhesion to a new substrate, the progeny of the multinucleate cells is more numerous than the sibling cells generated from uninucleate amoebae. Hence, multinucleate amoebae show an advantage for population growth when the number of cells is quantified over time. Multiple nuclei per cell are observed in different amoeba species, and the lack of adhesion induces multinuclearity in diverse protists such as Acanthamoeba castellanii, Vermamoeba vermiformis, Naegleria gruberi and Hartmannella rhysodes. In this study, we observe that agitation induces a cytokinesis delay, which promotes multinuclearity. Hence, we propose the hypothesis that multinuclearity represents a physiological adaptation under non-adherent conditions that can lead to biologically relevant advantages.

Spatio-temporal survey of opportunistic premise plumbing pathogens in the Paris drinking water distribution system

Opportunistic premise plumbing pathogens present in drinking water are linked to a significant number of infections for health compromised patients. However, their monitoring is not required in current water potability standards and they have been poorly studied in a full-scale network. In this study, we quantified, by qPCR, three opportunistic pathogens, Mycobacterium spp., Legionella pneumophila, Pseudomonas aeruginosa throughout the Paris drinking water network over a one-year sampling campaign. While Mycobacteria spp. seemed ubiquitous whatever the distribution system and the time of the year, the occurrence of L. pneumophila and P. aeruginosa showed seasonal variations. Unlike L. pneumophila and P. aeruginosa, the concentration (copies number/L) of Mycobacterium spp. varied between sampling sites. The variation in microbial numbers did not demonstrate any correlations with temperature, pH, chlorine, conductivity, orthophosphate or nitrate levels. In conclusion, Mycobacterium spp. are common inhabitants of the Paris network while L. pneumophila and P. aeruginosa presence fluctuate over space and time. Such qPCR approach would help to better understand the behaviour of opportunistic premise plumbing pathogens.

Free-living amoebae and squatters in the wild: ecological and molecular features

Free-living amoebae are protists frequently found in water and soils. They feed on other microorganisms, mainly bacteria, and digest them through phagocytosis. It is accepted that these amoebae play an important role in the microbial ecology of these environments. There is a renewed interest for the free-living amoebae since the discovery of pathogenic bacteria that can resist phagocytosis and of giant viruses, underlying that amoebae might play a role in the evolution of other microorganisms, including several human pathogens. Recent advances, using molecular methods, allow to bring together new information about free-living amoebae. This review aims to provide a comprehensive overview of the newly gathered insights into (1) the free-living amoeba diversity, assessed with molecular tools, (2) the gene functions described to decipher the biology of the amoebae and (3) their interactions with other microorganisms in the environment.

Microbiome of drinking water: A full-scale spatio-temporal study to monitor water quality in the Paris distribution system

The microbiological water quality of drinking water distribution system (DWDS) is of primary importance for human health. High-throughput sequencing has gained more and more attention in the last decade to describe this microbial diversity in water networks. However, there are few studies describing this approach on large drinking water distribution systems and for extended periods of time. To fill this gap and observe the potential subtle variation in microbiota of a water network through time and space, we aimed to apply high-throughput sequencing of the 16S rRNA gene approach to characterize bacterial communities of the Paris' DWDS over a one-year period. In this study, the Paris network, composed of four different DWDSs, was sampled at 31 sites, each month for one year. The sampling campaign was one of the largest described so far (n = 368) and the importance of key spatio-temporal and physico-chemical parameters was investigated. Overall, 1321 taxa were identified within the Paris network, although only fifteen of them were found in high relative abundance (>1%) in all samples. Two genera, Phreatobacter and Hyphomicrobium were dominant. The whole bacterial diversity was not significantly affected between the four DWDSs (spatial parameter) and by physico-chemical parameters. However, the bacterial diversity was slightly modified over the one-year period (temporal parameter) as we were able to observe DWDS microbiome perturbations, presumably linked to a preceding flood event. Comparison of high-throughput sequencing of the 16S rRNA gene amplicons vs. cultivation-based techniques showed that only 1.8% of bacterial diversity was recovered through cultivation. High throughput sequencing has made it possible to monitor DWDS more accurately than conventional methods by describing the whole diversity and detecting slight fluctuations in bacterial communities. This method would be further used to supervise drinking water networks, to follow any perturbations due to internals events (such as treatments) or external events (such as flooding).

Targeted Metagenomics of Microbial Diversity in Free-Living Amoebae and Water Samples

The presence of Legionella spp. in natural and man-made water systems is a great public health concern and heavily depends on the presence of free-living amoebae. Taking advantage of the development and affordability of next-generation sequencing technology, we present here a method to characterize the whole bacterial community directly from water samples, as well as from isolated free-living amoebae.

Environmental Mycobacterium avium subsp. paratuberculosis Hosted by Free-Living Amoebae

Mycobacterium avium subsp. paratuberculosis is responsible for paratuberculosis in animals. This disease, leading to an inflammation of the gastrointestinal tract, has a high impact on animal health and an important economic burden. The environmental life cycle of M. avium subsp. paratuberculosis is poorly understood and several studies suggest that free-living amoebae (FLA) might be a potential environmental host. FLA are protozoa found in water and soil that are described as reservoirs of pathogenic and non-pathogenic bacteria in the environment. Indeed, bacteria able to survive within these amoebae would survive phagocytosis from immune cells. In this study, we assessed the in vitro interactions between several strains of M. avium subsp. paratuberculosis and Acanthamoeba castellanii. The results indicate that the bacteria were able to grow within the amoeba and that they can survive for several days within their host. To explore the presence of M. avium subsp. paratuberculosis in environmental amoebae, we sampled water from farms positive for paratuberculosis. A M. avium subsp. paratuberculosis strain was detected within an environmental amoeba identified as related to the poorly described Rosculus genus. The bacterial strain was genotyped, showing that it was similar to previous infectious strains isolated from cattle. In conclusion, we described that various M. avium subsp. paratuberculosis strains were able to grow within amoebae and that these bacteria could be found on farm within amoebae isolated from the cattle environment. It validates that infected amoebae might be a reservoir and vector for the transmission of M. avium subsp. paratuberculosis.

Legionella pneumophila decreases velocity of Acanthamoeba castellanii

Acanthamoeba castellanii is a free-living amoeba commonly found in aquatic environment. It feeds on bacteria even if some bacteria resist amoebal digestion. Thus, A. castellanii is described as a Trojan horse able to harbor pathogenic bacteria. L. pneumophila is one of the amoeba-resisting bacteria able to avoid host degradation by phagocytosis and to multiply inside the amoeba. When infecting its host, L. pneumophila injects hundreds of effectors via a type IV secretion system that change physiology of the amoeba to its profit. In this study, we assess mobility of A. castellanii upon infection with L. pneumophila. Electron-microscopy analysis of amoebae revealed a reduction of acanthopodia on cells infected with L. pneumophila. Analysis of velocity showed that migration of A. castellanii infected with L. pneumophila was significantly impaired compare to uninfected cells. Taken together, infection with L. pneumophila could prevent formation of cytoplasmic extensions such as acanthopodia with consequences on the shape, adherence and mobility of A. castellanii.

Environmental factors shaping cultured free-living amoebae and their associated bacterial community within drinking water network

Free-living amoebae (FLA) constitute an important part of eukaryotic populations colonising drinking water networks. However, little is known about the factors influencing their ecology in such environments. Because of their status as reservoir of potentially pathogenic bacteria, understanding environmental factors impacting FLA populations and their associated bacterial community is crucial. Through sampling of a large drinking water network, the diversity of cultivable FLA and their bacterial community were investigated by an amplicon sequencing approach, and their correlation with physicochemical parameters was studied. While FLA ubiquitously colonised the water network all year long, significant changes in population composition were observed. These changes were partially explained by several environmental parameters, namely water origin, temperature, pH and chlorine concentration. The characterisation of FLA associated bacterial community reflected a diverse but rather stable consortium composed of nearly 1400 OTUs. The definition of a core community highlighted the predominance of only few genera, majorly dominated by Pseudomonas and Stenotrophomonas. Co-occurrence analysis also showed significant patterns of FLA-bacteria association, and allowed uncovering potentially new FLA - bacteria interactions. From our knowledge, this study is the first that combines a large sampling scheme with high-throughput identification of FLA together with associated bacteria, along with their influencing environmental parameters. Our results demonstrate the importance of physicochemical parameters in the ecology of FLA and their bacterial community in water networks.

Characterization of biofilm formation in natural water subjected to low-frequency electromagnetic fields

Electromagnetic field (EMF) treatment has proven to be effective against mineral scaling in water systems. Therefore, it should be assessed for the treatment of other deposits such as biofilms. In this study, a commercial device producing low-frequency EMF (1-10 kHz) was applied to a reactor fed with natural water for 45 days. The treatment promoted the concentration of microorganisms in suspension and limited the amount of sessile microorganisms in the biofilm, as determined by the measurement of total DNA, qPCR and microscopy. The structure of the bacterial community was assessed by t-RFLP and pyrosequencing analysis. The results showed that EMF treatment affected both planktonic and sessile community composition. EMFs were responsible for a shift in classes of Proteobacteria during development of the biofilm. It may be speculated that the EMF treatment affected particle solubility and/or microorganism hydration. This study indicated that EMFs modulated biofilm formation in natural water.

Shedding light on microbial dark matter: a TM6 bacterium as natural endosymbiont of a free-living amoeba

The TM6 phylum belongs to the so-called microbial dark matter that gathers uncultivated bacteria detected only via DNA sequencing. Recently, the genome sequence of a TM6 bacterium (TM6SC1) has led to suggest that this bacterium would adopt an endosymbiotic life. In the present paper, free-living amoebae bearing a TM6 strain were isolated from a water network. The amoebae were identified as Vermamoeba vermiformis and the presence of a TM6 strain was detected by polymerase chain reaction and microscopy. The partial sequence of its 16S rRNA gene showed this strain to be closely related to the sequenced TM6SC1 strain. These bacteria displayed a pyriform shape and were found within V. vermiformis. Therefore, these bacteria were named Vermiphilus pyriformis. Interactions studies showed that V. pyriformis was highly infectious and that its relation with V. vermiformis was specific and highly stable. Finally, it was found that V. pyriformis inhibited the encystment of V. vermiformis. Overall, this study describes for the first time an endosymbiotic relationship between a TM6 bacterium and a free-living amoeba in the environment. It suggests that other bacteria of the TM6 phylum might also be endosymbiotic bacteria and may be found in other free-living amoebae or other organisms.

Sensitivity of Vermamoeba (Hartmannella) vermiformis cysts to conventional disinfectants and protease

Vermamoeba vermiformis is a free-living amoeba (FLA) widely distributed in the environment, known to colonize hot water networks and to be the reservoir of pathogenic bacteria such as Legionella pneumophila. FLA are partly resistant to biocides, especially in their cyst form. The control of V. vermiformis in hot water networks represents an important health issue, but there are very few data on their resistance to disinfection treatments. The sensitivity of cysts of two strains of V. vermiformis to three disinfectants frequently used in hot water networks (chlorine, heat shock, peracetic acid (PAA) mixed with hydrogen peroxide (H2O2)) was investigated. In vitro, several concentrations of biocides, temperatures and exposure times according to the French regulation were tested. Cysts were fully inactivated by the following conditions: 15 mg/L of chlorine for 10 min; 60 °C for 30 min; and 0.5 g/L equivalent H2O2 of PAA mixed with H2O2 for 30 min. For the first time, the strong efficacy of subtilisin (0.625 U/mL for 24 h), a protease, to inactivate the V. vermiformis cysts has been demonstrated. It suggests that novel approaches may be efficient for disinfection processes. Finally, V. vermifomis cysts were sensitive to all the tested treatments and appeared to be more sensitive than Acanthamoeba cysts.

First evidence of amoebae-mycobacteria association in drinking water network

Free-living amoebae are protozoa ubiquitously found in water systems. They mainly feed on bacteria by phagocytosis, but some bacterial species are able to resist or even escape this lethal process. Among these amoeba resistant bacteria are numerous members of the genus Mycobacterium. Nontuberculous Mycobacteria (NTM) are opportunistic pathogens that share the same ecological niches as amoebae. While several studies have demonstrated the ability of these bacteria to colonise and persist within drinking water networks, there is also strong suspicion that mycobacteria could use amoebae as a vehicle for protection and even replication. We investigated here the presence of NTM and FLA on a drinking water network during an all year round sampling campaign. We observed that 87.6% of recovered amoebal cultures carried high numbers of NTM. Identification of these amoeba and mycobacteria strains indicated that the main genera found in drinking water networks, that is, Acanthamoeba, Vermamoeba, Echinamoeba, and Protacanthamoeba are able to carry and likely to allow replication of several environmental and potentially pathogenic mycobacteria including M. llatzerense and M. chelonae. Direct Sanger sequencing as well as pyrosequencing of environmental isolates demonstrated the frequent association of mycobacteria and FLA, as they are part of the most represented genera composing amoebae's microbiome. This is the first time that an association between FLA and NTM is observed in water networks, highlighting the importance of FLA in the ecology of NTM.

IroT/mavN, a new iron-regulated gene involved in Legionella pneumophila virulence against amoebae and macrophages

Legionella pneumophila is a pathogenic bacterium commonly found in water. Eventually, it could be transmitted to humans via inhalation of contaminated aerosols. Iron is known as a key requirement for the growth of L. pneumophila in the environment and within its hosts. Many studies were performed to understand iron utilization by L. pneumophila but no global approaches were conducted. In this study, transcriptomic analyses were performed, comparing gene expression in L. pneumophila in standard versus iron restricted conditions. Among the regulated genes, a newly described one, lpp_2867, was highly induced in iron-restricted conditions. Mutants lacking this gene in L. pneumophila were not affected in siderophore synthesis or utilization. On the contrary, they were defective for growth on iron-depleted solid media and for ferrous iron uptake. A sequence analysis predicts that Lpp_2867 is a membrane protein, suggesting that it is involved in ferrous iron transport. We thus named it IroT, for iron transporter. Infection assays showed that the mutants are highly impaired in intracellular growth within their environmental host Acanthamoeba castellanii and human macrophages. Taken together, our results show that IroT is involved, directly or indirectly, in ferrous iron transport and is a key virulence factor for L. pneumophila.

Encystment of Vermamoeba (Hartmannella) vermiformis: Effects of environmental conditions and cell concentration

Vermamoeba vermiformis is a free-living amoeba (FLA) which is widely distributed in the environment. It is known to colonize water systems and to be a reservoir of pathogenic bacteria, such as Legionella pneumophila. For these reasons the control of V. vermiformis represents an important health issue. However, FLA may be resistant to disinfection treatments due to the process of encystment. Thereby, it is important to better understand factors influencing this process. In this aim, we investigated the effect of temperature, pH, osmotic pressure and cell concentration on the encystment of two V. vermiformis strains. Encystment was quite fast, with a 100% encystment rate being observed after 9h of incubation. For the two strains, an optimal encystment was obtained at 25 and 37°C. Concerning pH and osmotic pressure, there were different effects on the encystment according to the tested strains. For the reference strain (ATCC 50237), the patterns of encystment were similar for pH comprised between 5 and 9 and for KCl concentrations ranging from 0.05 to 0.2 mol L(-1). For the environmental strain (172A) an optimal encystment was obtained for basic pH (8 and 9) and for a concentration in KCl of 0.1 mol L(-1). The results also clearly demonstrated that the encystment rate increased with cell concentration, suggesting that there is an inter-amoebal communication. The present study establish for the first time environmental conditions favoring encystment and would lay the foundations to better control the encystment of V. vermiformis.

Microbiome of free-living amoebae isolated from drinking water

Free-living amoebae (FLA) are protozoa that can be found in water networks where they prey on bacteria within biofilms. Most bacteria are digested rapidly by phagocytosis, however some are able to survive within amoebae and some are even able to multiply, as it is the case for Legionella pneumophila. These resisting bacteria are a potential health problem as they could also resist to macrophage phagocytosis. Several publications already reported intra-amoebal bacteria but the methods of identification did not allow metagenomic analysis and are partly based on co-culture with one selected amoebal strain. The aim of our study was to conduct a rRNA-targeted metagenomic analysis on amoebae and intra-amoebal bacteria found in drinking water network, to provide the first FLA microbiome in environmental strains. Three sites of a water network were sampled during four months. Culturable FLA were isolated and total DNA was prepared, allowing purification of both amoebal and bacterial DNA. Metagenomic studies were then conducted through 18S or 16S amplicons sequencing. Hartmannella was by far the most represented genus of FLA. Regarding intra-amoebal bacteria, 54 genera were identified, among which 21 were newly described intra-amoebal bacteria, underlying the power of our approach. There were high differences in bacterial diversity between the three sites. Several genera were highly represented and/or found at least in two sites, underlying that these bacteria could be able to multiply within FLA. Our method is therefore useful to identify FLA microbiome and could be applied to other networks to have a more comprehensive view of intra-amoebal diversity.

Sensitivity of free-living amoeba trophozoites and cysts to water disinfectants

Free-living amoebae are naturally present in water. These protozoa could be pathogenic and could also shelter pathogenic bacteria. Thus, they are described as a potential hazard for health. Also, free-living amoebae have been described to be resistant to biocides, especially under their cyst resistant form. There are several studies on amoeba treatments but none of them compare sensitivity of trophozoites and cysts from different genus to various water disinfectants. In our study, we tested chlorine, monochloramine and chlorine dioxide on both cysts and trophozoites from three strains, belonging to the three main genera of free-living amoebae. The results show that, comparing cysts to trophozoites inactivation, only the Acanthamoeba cysts were highly more resistant to treatment than trophozoites. Comparison of the disinfectant efficiency led to conclude that chlorine dioxide was the most efficient treatment in our conditions and was particularly efficient against cysts. In conclusion, our results would help to adapt water treatments in order to target free-living amoebae in water networks.

Natural biofilm formation with Legionella pneumophila

Biofilm formation could be studied in various conditions. Most of the studies with Legionella pneumophila used monospecies biofilm in culture media. In some cases, it is important to study bacteria in conditions more close to environmental conditions. In this paper, we describe protocols to produce natural biofilms from river water that were spiked with L. pneumophila.

Detection of free-living amoebae by using multiplex quantitative PCR

Free-living amoebae (FLA) are protozoa found worldwide in soil and aquatic environments, which are able to colonize man-made water networks. Some FLA have the potential to be pathogenic and others might harbour pathogenic bacteria. Indeed, FLA feed on bacteria, but some bacteria could resist phagocytosis and either survive in FLA or even multiply within FLA. These bacteria are collectively named amoeba resistant bacteria (ARB). The best characterized example is Legionella pneumophila, for which FLA is the main reservoir in the environment. Not only could FLA be a reservoir that protects ARB, some bacteria might become more resistant to treatment and be more virulent. Thus, it is of medical significance to quantify FLA populations in soil, water or the environment. The main limitation for the quantification of FLA is that classical culture is not efficient and reliable for many genera and 'strains'. Thus, several PCR-based quantification methods have been published for various FLA. However, thus far, no method has been published to simultaneously quantify the main FLA genera in the same PCR reaction. In this study, we developed a multiplex qPCR method to detect both Amoebozoan (i.e. Acanthamoeba, Hartmannella and Echinamoeba) and Vahlkampfiidae (i.e. Vahlkampfia and Naegleria) using 18S ribosomal RNA as the target gene. This method was shown to be specific, reliable and sensitive, could be used for the quantification of FLA and is likely to be useful to anticipate risks due to FLA or pathogenic bacteria, such as L. pneumophila.

Legionella pneumophila transcriptional response to chlorine treatment

Legionella pneumophila is a ubiquitous environmental microorganism found in freshwater that can cause an acute form of pneumonia known as Legionnaires' disease. Despite widespread use of chlorine to ensure drinking water quality and awareness that L. pneumophila may escape these treatments, little is known about its effects on L. pneumophila. The aim of this study was to investigate the L. pneumophila transcriptional response induced by chlorine treatment. Transcriptome analysis, using DNA arrays, showed that a sublethal dose of chlorine induces a differential expression of 391 genes involved in stress response, virulence, general metabolism, information pathways and transport. Many of the stress response genes were significantly upregulated, whereas a significant number of virulence genes were repressed. In particular, exposure of L. pneumophila to chlorine induced the expression of cellular antioxidant proteins, stress proteins and transcriptional regulators. In addition, glutathione S-transferase specific activity was enhanced following chlorine treatment. Our results clearly indicate that chlorine induces expression of proteins involved in cellular defence mechanisms against oxidative stress that might be involved in adaptation or resistance to chlorine treatment.

Anti-Legionella activity of staphylococcal hemolytic peptides

A collection of various Staphylococci was screened for their anti-Legionella activity. Nine of the tested strains were found to secrete anti-Legionella compounds. The culture supernatants of the strains, described in the literature to produce hemolytic peptides, were successfully submitted to a two step purification process. All the purified compounds, except one, corresponded to previously described hemolytic peptides and were not known for their anti-Legionella activity. By comparison of the minimal inhibitory concentrations, minimal permeabilization concentrations, decrease in the number of cultivable bacteria, hemolytic activity and selectivity, the purified peptides could be separated in two groups. First group, with warnericin RK as a leader, corresponds to the more hemolytic and bactericidal peptides. The peptides of the second group, represented by the PSMα from Staphylococcus epidermidis, appeared bacteriostatic and poorly hemolytic.

Efficiency of water disinfectants against Legionella pneumophila and Acanthamoeba

Free-living amoebae might be pathogenic by themselves and be a reservoir for bacterial pathogens, such as Legionella pneumophila. Not only could amoebae protect intra-cellular Legionella but Legionella grown within amoebae could undergo physiological modifications and become more resistant and more virulent. Therefore, it is important to study the efficiency of treatments on amoebae and Legionella grown within these amoebae to improve their application and to limit their impact on the environment. With this aim, we compared various water disinfectants against trophozoites of three Acanthamoeba strains and L. pneumophila alone or in co-culture. Three oxidizing disinfectants (chlorine, monochloramine, and chlorine dioxide) were assessed. All the samples were treated with disinfectants for 1 h and the disinfectant concentration was followed to calculate disinfectant exposure (Ct). We noticed that there were significant differences of susceptibility among the Acanthamoeba strains. However no difference was observed between infected and non-infected amoebae. Also, the comparison between the three disinfectants indicates that monochloramine was efficient at the same level towards free or co-cultured L. pneumophila while chlorine and chlorine dioxide were less efficient on co-cultured L. pneumophila. It suggests that these disinfectants should have different modes of action. Finally, our results provide for the first time disinfectant exposure values for Acanthamoeba treatments that might be used as references for disinfection of water systems.

Fatty acid composition modulates sensitivity of Legionella pneumophila to warnericin RK, an antimicrobial peptide

Warnericin RK is an antimicrobial peptide, produced by a Staphyloccocus warneri strain, described to be specifically active against Legionella, the pathogenic bacteria responsible for Legionnaires' disease. Warnericin RK is an amphiphilic alpha-helical peptide, which possesses a detergent-like mode of action. Two others peptides, δ-hemolysin I and II, produced by the same S. warneri strain, are highly similar to S. aureus δ-hemolysin and also display anti-Legionella activity. It has been recently reported that S. aureus δ-hemolysin activity on vesicles is likewise related to phospholipid acyl-chain structure, such as chain length and saturation. As staphylococcal δ-hemolysins were highly similar, we thus hypothesized that fatty acid composition of Legionella's membrane might influence the sensitivity of the bacteria to warnericin RK. Relationship between sensitivity to the peptide and fatty acid composition was then followed in various conditions. Cells in stationary phase, which were already described as less resistant than cells in exponential phase, displayed higher amounts of branched-chain fatty acids (BCFA) and short chain fatty acids. An adapted strain, able to grow at a concentration 33 fold higher than minimal inhibitory concentration of the wild type (i.e. 1μM), was isolated after repeated transfers of L. pneumophila in the presence of increased concentrations of warnericin RK. The amount of BCFA was significantly higher in the adapted strain than in the wild type strain. Also, a transcriptomic analysis of the wild type and adapted strains showed that two genes involved in fatty acid biosynthesis were repressed in the adapted strain. These genes encode enzymes involved in desaturation and elongation of fatty acids respectively. Their repression was in agreement with the decrease of unsaturated fatty acids and fatty acid chain length in the adapted strain. Conclusively, our results indicate that the increase of BCFA and the decrease of fatty acid chain length in membrane were correlated with the increase in resistance to warnericin RK. Therefore, fatty acid profile seems to play a critical role in the sensitivity of L. pneumophila to warnericin RK.

Detergent-like activity and alpha-helical structure of warnericin RK, an anti-Legionella peptide

Warnericin RK is the first antimicrobial peptide known to be active against Legionella pneumophila, a pathogen bacterium that is responsible for severe pneumonia. Strikingly, this peptide displays a very narrow range of antimicrobial activity, almost limited to the Legionella genus, and a hemolytic activity. A similar activity has been described for delta-lysin, a well-known hemolytic peptide of Staphylococci that has not been described as antimicrobial. In this study we aimed to understand the mode of action of warnericin RK and to explain its particular target specificity. We found that warnericin RK permeabilizes artificial membranes in a voltage-independent manner. Osmotic protection experiments on erythrocytes showed that warnericin RK does not form well-defined pores, suggesting a detergent-like mode of action, as previously described for delta-lysin at high concentrations. Warnericin RK also permeabilized Legionella cells, and these cells displayed a high sensitivity to detergents. Depending on the detergent used, Legionella was from 10- to 1000-fold more sensitive than the other bacteria tested. Finally, the structure of warnericin RK was investigated by means of circular dichroism and NMR spectroscopy. The peptide adopted an amphiphilic alpha-helical structure, consistent with the proposed mode of action. We conclude that the specificity of warnericin RK toward Legionella results from both the detergent-like mode of action of the peptide and the high sensitivity of these bacteria to detergents.

delta-hemolysin, an update on a membrane-interacting peptide

delta-hemolysin is a hemolytic peptide produced by Staphylococcus, and it has been studied for nearly 50 years. Therefore, it has become a model in the study of peptides interacting with membranes. In this review, we report some recent findings and compare them with previous works. delta-hemolysin is a 26 amino acid peptide, somewhat hydrophobic and presenting a zero net charge. Study of its structure has shown that delta-hemolysin is alpha-helical and amphipathic, such as many antimicrobial peptides (e.g. magainin and melittin). However, delta-hemolysin had not displayed any reported antimicrobial activity until a recent publication showed its high potency against Legionella. Its mode of action is based on direct interaction with target membranes. In accordance with its concentration, delta-hemolysin may slightly perturb a membrane or lead to cell lysis. Peptide charge plays an important role in its interaction with membranes, as is shown in the study of peptide variants. Some positively charged variants become highly hemolytic and even active against Escherichia coli and Staphylococcus aureus. Finally, it has recently been demonstrated that peptide preferentially binds to lipid-disordered domains. It has been postulated that as a result, enrichment in lipid-ordered domains might increase peptide concentration in lipid-disordered domains and thereby improve its activity.

Characterization of anti-Legionella activity of warnericin RK and delta-lysin I from Staphylococcus warneri

Legionella pneumophila, the causative agent of Legionnaires' disease, is a waterborne bacteria. It can multiply in man-made water systems and infect people who inhale contaminated droplets. We have previously reported a Staphylococcus warneri strain that display an anti-Legionella activity. In this work, we characterized three anti-Legionella peptides that are produced by S. warneri. One peptide, warnericin RK, is original, while the two others are delta-lysin I and delta-lysin II, whose genes were previously described. Due to high sequence similarity of the two delta-lysins, further characterization was performed only on delta-lysin I. Warnericin RK and delta-lysin I displayed the same antibacterial spectrum, which is almost restricted to the Legionella genus. Also, both peptides have a hemolytic activity. These results led to the hypothesis that warnericin RK and delta-lysin I share a similar mode of action, and that Legionella should have a specific feature that may explain the high specificity of these antibacterial peptides.

Long-term survival of Legionella pneumophila associated with Acanthamoeba castellanii vesicles

Legionella pneumophila, the causative agent of Legionnaires' disease, is ubiquitously found in aquatic environments, associated with free living amoebae. Trophozoite forms of the genus Acanthamoeba have been shown to support the intracellular growth of Legionella while it has been proposed that cyst forms are related to survival in harsh environments. This underlines that amoebae are of primary importance in Legionella spreading. In this study, we followed the survival of L. pneumophila Lens over 6 months in a poor medium, with or without Acanthamoeba castellanii. The results demonstrated that L. pneumophila Lens could survive for at least 6 months in association with A. castellanii and that cultivable bacteria are to be found within expelled vesicles rather than within cysts. Our findings suggest that vesicles might be further studied in order to elucidate their production and their role in the environmental spreading of Legionella.

The continuing story of class IIa bacteriocins

Many bacteria produce antimicrobial peptides, which are also referred to as peptide bacteriocins. The class IIa bacteriocins, often designated pediocin-like bacteriocins, constitute the most dominant group of antimicrobial peptides produced by lactic acid bacteria. The bacteriocins that belong to this class are structurally related and kill target cells by membrane permeabilization. Despite their structural similarity, class IIa bacteriocins display different target cell specificities. In the search for new antibiotic substances, the class IIa bacteriocins have been identified as promising new candidates and have thus received much attention. They kill some pathogenic bacteria (e.g., Listeria) with high efficiency, and they constitute a good model system for structure-function analyses of antimicrobial peptides in general. This review focuses on class IIa bacteriocins, especially on their structure, function, mode of action, biosynthesis, bacteriocin immunity, and current food applications. The genetics and biosynthesis of class IIa bacteriocins are well understood. The bacteriocins are ribosomally synthesized with an N-terminal leader sequence, which is cleaved off upon secretion. After externalization, the class IIa bacteriocins attach to potential target cells and, through electrostatic and hydrophobic interactions, subsequently permeabilize the cell membrane of sensitive cells. Recent observations suggest that a chiral interaction and possibly the presence of a mannose permease protein on the target cell surface are required for a bacteria to be sensitive to class IIa bacteriocins. There is also substantial evidence that the C-terminal half penetrates into the target cell membrane, and it plays an important role in determining the target cell specificity of these bacteriocins. Immunity proteins protect the bacteriocin producer from the bacteriocin it secretes. The three-dimensional structures of two class IIa immunity proteins have been determined, and it has been shown that the C-terminal halves of these cytosolic four-helix bundle proteins specify which class IIa bacteriocin they protect against.

Isolation and characterization of aStaphylococcus warneristrain producing an anti-Legionellapeptide

Legionella pneumophila is a pathogenic bacterium found in freshwater environments that is responsible for pneumonia. People become infected through inhalation of contaminated droplets from water devices, such as cooling towers and showers. It is important to find new treatments that decrease the development of Legionella. We found a Staphylococcus warneri strain that inhibits Legionella growth. This activity is due to a molecule secreted by S. warneri. This molecule displayed a high heat-stability and its activity was lost after protease treatments, suggesting that it might be a bacteriocin. Its purification led us to conclude that this anti-Legionella molecule is an highly hydrophobic peptide. It has an original and very specific spectrum of activity, directed only toward the Legionella genus. This is the first description of an antibacterial peptide active against Legionella.

Development of a real-time PCR assay for quantification of Acanthamoeba trophozoites and cysts

Free-living amoebae have been found to be a reservoir for various pathogenic bacteria in aquatic environments. For example, the Acanthamoeba genus renders possible the intracellular multiplication of Legionella pneumophila, which is responsible for legionellosis. It consequently matters to quantify Acanthamoeba cells and thereby enhance our assessment of the risk of contamination. The classical microbiological method of quantification relies on amoebae growth and most probable number calculation. We have developed a real-time PCR assay based on a TaqMan probe that hybridizes onto 18S rDNA. This probe is specific to the Acanthamoeba genus. The assay was successful with both the trophozoite and the cyst forms of Acanthamoeba. Highly sensitive, it proved to permit detection of fewer than 10 cells, even those that are not easily cultivable, such as the cyst forms.

Involvement of the mpo operon in resistance to class IIa bacteriocins in Listeria monocytogenes

High resistance to class IIa bacteriocins in Listeria monocytogenes has been clearly linked to lack of expression of the mptACD operon, encoding the EIIt Man mannose PTS permease. Also, intermediate resistance has been associated with membrane phospholipid modifications in the spontaneous mutants L. monocytogenes B73-V1 and B73-V2. We constructed a new mutant of L. monocytogenes that was interrupted in mpoA, and which also exhibited an intermediate resistance phenotype. The mpoABCD operon putatively encodes a PTS permease of the mannose family similar to that encoded by the mpt operon. In silico analysis indicated that mpo transcription might be dependent on sigma54. Our study demonstrated that the three intermediate resistant mutants have a slight decrease in mptACD expression, showing that the level of sensitivity is correlated to the level of mpt expression. We show a cross-regulation between mpo and mpt. In particular, the mpo mutant has a defect in mpt expression that possibly could explain its intermediate resistance phenotype.

Cell-surface alterations in class IIa bacteriocin-resistant Listeria monocytogenes strains

Strains of the food-borne pathogenListeria monocytogenes, showing either intermediate or high-level resistance to class IIa bacteriocins, were investigated to determine characteristics that correlated with their sensitivity levels. Two intermediate and one highly resistant spontaneous mutant ofL. monocytogenesB73, a highly resistant mutant ofL. monocytogenes412, and a highly resistant, defined (mptA) mutant ofL. monocytogenesEGDe were compared with their respective wild-type strains in order to investigate the contribution of different factors to resistance. Decreased mannose-specific phosphotransferase system gene expression (mptA, EIIABMancomponent) was implicated in all levels of resistance, confirming previous studies by the authors' group. However, a clear correlation betweend-alanine content in teichoic acid (TA), in particular the alanine : phosphorus ratio, and a more positive cell surface, as determined by cytochromecbinding, were found for the highly resistant strains. Furthermore, two of the three highly resistant strains showed a significant increase in sensitivity towardsd-cycloserine (DCS). However, real-time PCR of thedltA(d-alanine esterification), anddalandddlAgenes (peptidoglycan biosynthesis) showed no change in transcriptional levels. The link between DCS sensitivity and increasedd-alanine esterification of TA may be that DCS competes with alanine for transport via the alanine transporter. A possible tendency towards increased lysinylation of membrane phospholipid in the highly resistant strains was also found. A previous study reported that cell membranes of all the resistant strains, including the intermediate resistant strains, contained more unsaturated phosphatidylglycerol, which is an indication of a more fluid cell membrane. The results of that study correlate with the possible lysinylation, decreasedmptAexpression,d-alanine esterification of TA and more positive cell surface charge found in this study for resistant strains. The authors' findings strongly indicate that all these factors could contribute to class IIa bacteriocin resistance and that the combination and contribution of each of these factors determine the level of bacteriocin resistance.

Expression of mptC of Listeria monocytogenes induces sensitivity to class IIa bacteriocins in Lactococcus lactis

Sensitivity to class IIa bacteriocins from lactic acid bacteria was recently associated with the mannose phosphotransferase system (PTS) permease, , in Listeria monocytogenes. To assess the involvement of this protein complex in class IIa bacteriocin activity, the mptACD operon, encoding , was heterologously expressed in an insensitive species, namely Lactococcus lactis, using the NICE double plasmid system. Upon induction of the cloned operon, the recombinant Lc. lactis became sensitive to leucocin A. Pediocin PA-1 and enterocin A also showed inhibitory activity against Lc. lactis cultures expressing mptACD. Furthermore, the role of the three genes of the mptACD operon was investigated. Derivative plasmids containing various combinations of these three genes were made from the parental mptACD plasmid by divergent PCR. The results showed that expression of mptC alone is sufficient to confer sensitivity to class IIa bacteriocins in Lc. lactis.

Global analysis of gene expression in an rpoN mutant of Listeria monocytogenes

The role of the alternative sigma(54) factor, encoded by the rpoN gene, was investigated in Listeria monocytogenes by comparing the global gene expression of the wild-type EGDe strain and an rpoN mutant. Gene expression, using whole-genome macroarrays, and protein content, using two-dimensional gel electrophoresis, were analysed. Seventy-seven genes and nine proteins, whose expression was modulated in the rpoN mutant as compared to the wild-type strain, were identified. Most of the modifications were related to carbohydrate metabolism and in particular to pyruvate metabolism. However, under the conditions studied, only the mptACD operon was shown to be directly controlled by sigma(54). Therefore, the remaining modifications seem to be due to indirect effects. In parallel, an in silico analysis suggests that sigma(54) may directly control the expression of four different phosphotransferase system (PTS) operons, including mptACD. PTS activity is known to have a direct effect on the pyruvate pool and on catabolite regulation. These results suggest that sigma(54) is mainly involved in the control of carbohydrate metabolism in L. monocytogenes via direct regulation of PTS activity, alteration of the pyruvate pool and modulation of carbon catabolite regulation.

Characterization of a unique σ54–dependent PTS operon of the lactose family in Listeria monocytogenes

The sigma(54) subunit of the RNA polymerase directs the expression of specific operons in association with cognate activators. Three different activators have been detected in the Listeria monocytogenes genome on the basis of the high conservation of a specific domain. Among them, the LacR activator, of the LevR family, was found just upstream from a newly described sigma(54)-dependent operon, lpo, which presents a classical -24/-12 consensus promoter. The lpo operon encodes proteins similar to subunits of a PTS permease (EII) of the lactose family, namely LpoA (IIA) and LpoB (IIB). It also encodes a third putative protein, LpoO, with an unknown function but sharing high similarity with proteins also encoded within PTS operons from other bacteria and bearing a RGD motif. The expression of lpo was clearly dependent on LacR and sigma(54), and was induced by cellobiose, chitobiose and lactose. It underlies that the lpo operon likely encodes proteins involved in the utilization of these sugars by L. monocytogenes.

High-level resistance to class IIa bacteriocins is associated with one general mechanism in Listeria monocytogenes

Class IIa bacteriocins may be used as natural food preservatives, yet resistance development in the target organisms is still poorly understood. In this study, the understanding of class IIa resistance development in Listeria monocytogenes is extended, linking the seemingly diverging results previously reported. Eight resistant mutants having a high resistance level (at least a 10(3)-fold increase in MIC), originating from five wild-type listerial strains, were independently isolated following exposure to four different class IIa bacteriocin-producing lactic acid bacteria (including pediocin PA-1 and leucocin A producers). Two of the mutants were isolated from food model systems (a saveloy-type sausage at 10 degrees C, and salmon juice at 5 degrees C). Northern blot analysis showed that the eight mutants all had increased expression of EII(Bgl) and a phospho-beta-glucosidase homologue, both originating from putative beta-glucoside-specific phosphoenolpyruvate-dependent phosphotransferase systems (PTSs). However, disruption of these genes in a resistant mutant did not confer pediocin sensitivity. Comparative two-dimensional gel analysis of proteins isolated from mutant and wild-type strains showed that one spot was consistently missing in the gels from mutant strains. This spot corresponded to the MptA subunit of the mannose-specific PTS, found only in the gels of wild-type strains. The mptACD operon was recently shown to be regulated by the sigma(54) transcription factor in conjunction with the activator ManR. Class IIa bacteriocin-resistant mutants having defined mutations in mpt or manR also exhibited the two diverging PTS expression changes. It is suggested here that high-level class IIa resistance in L. monocytogenes and at least some other Gram-positive bacteria is developed by one prevalent mechanism, irrespective of wild-type strain, class IIa bacteriocin, or the tested environmental conditions. The changes in expression of the beta-glucoside-specific and the mannose-specific PTS are both influenced by this mechanism. The current understanding of the actual cause of class IIa resistance is discussed.

Mode of action of modified and unmodified bacteriocins from Gram-positive bacteria

The antibiotic activity of bacteriocins from Gram-positive bacteria, whether they are modified (class I bacteriocins, lantibiotics) or unmodified (class II), is based on interaction with the bacterial membrane. However, recent work has demonstrated that for many bacteriocins, generalised membrane disruption models as elaborated for amphiphilic peptides (e.g. tyriodal pore or carpet model) cannot adequately describe the bactericidal action. Rather, specific targets seem to be involved in pore formation and other activities. For the nisin and epidermin family of lantibiotics, the membrane-bound cell wall precursor lipid II has recently been identified as target. The duramycin family of lantibiotics binds specifically to phosphoethanolamine which results in inhibition of phospholipase A2 and various other cellular functions. Most of the class II bacteriocins dissipate the proton motive force (PMF) of the target cell, via pore formation. The subclass IIa bacteriocin activity likely depends on a mannose permease of the phosphotransferase system (PTS) as specific target. The subclass IIb bacteriocins (two-component) also induce dissipation of the PMF by forming cation- or anion-specific pores; specific targets have not yet been identified. Finally, the subclass IIc comprises miscellaneous peptides with various modes of action such as membrane permeabilization, specific inhibition of septum formation and pheromone activity.

A sigma(54)-dependent PTS permease of the mannose family is responsible for sensitivity of Listeria monocytogenes to mesentericin Y105

Sensitivity of Listeria monocytogenes to the bacteriocin mesentericin Y105 was previously shown to be dependent on the sigma(54) subunit of the RNA polymerase. This points towards expression of particular sigma(54)-dependent genes. The present study describes first, ManR, a new sigma(54)-associated activator, and second, Ell(t)(Man), a new sigma(54)-dependent PTS permease of the mannose family, both involved in sensitivity to mesentericin Y105, since interruption of their corresponding genes led to resistance of L. monocytogenes EGDe. Ell(t)(Man) is likely composed of three subunits encoded by the mpt operon (mptA, mptC and mptD genes). Interruption of either the proximal (mptA) or distal (mptD) gene led to resistance, supporting results obtained in Enterococcus faecalis. Accordingly, such PTS permeases of the mannose family should be involved in sensitivity of different target strains to mesentericin Y105. In L. monocytogenes, expression of the mpt operon is shown to be controlled by sigma(54) and ManR and to be induced by both glucose and mannose. The latter result indicates that these sugars are transported by the Ell(t)(Man) permease. Moreover, these sugars correlatively induce sensitivity of L. monocytogenes to mesentericin Y105, strongly favouring the primary role of Ell(t)(Man). MptD, a membrane subunit of Ell(t)(Man), presents an additional domain compared to most IID(Man) subunits described in data banks. An in-frame deletion of this domain in mptD led to resistance of L. monocytogenes, showing its connection with sensitivity and suggesting that it could be directly involved in the recognition of the target cell by mesentericin Y105. Taken together, the results of this work demonstrate that Ell(t)(Man) is prominent in sensitivity to mesentericin Y105 and could be a receptor for subclass IIa bacteriocins.

Analysis of sigma(54)-dependent genes in Enterococcus faecalis: a mannose PTS permease (EII(Man)) is involved in sensitivity to a bacteriocin, mesentericin Y105

The sigma(54) RNA polymerase subunit has a prominent role in susceptibility of Listeria monocytogenes and Enterococcus faecalis to mesentericin Y105, a class IIa bacteriocin. Consequently, sigma(54)-dependent genes as well as specific activators also required for expression of these genes were sought. Five putative sigma(54)-associated activators were detected in the genome of E. faecalis V583, and all but one could activate the transcription of permease genes belonging to sugar phosphotransferase systems (PTSs). Interestingly, these activators display a helicase signature not yet reported in this activator family, which could explain the ATP-dependent mechanism of DNA unwinding preceding the start of transcription. To find which activator is linked to susceptibility of E. faecalis to mesentericin Y105, their respective genes were subsequently interrupted. Among them, only mptR gene interruption led to a resistance phenotype. Immediately downstream from mptR, a putative sigma(54)-dependent operon was found to encode a mannose PTS permease, namely EII(t)(Man). Moreover, in liquid culture, glucose and mannose induced the sensitivity of E. faecalis to mesentericin Y105. Since sugars have previously been reported to induce PTS permease expression, it appears that EII(t)(Man) expression, presumably induced in the presence of glucose and mannose, leads to an enhanced sensitivity of E. faecalis to the bacteriocin. Additional information was gained from knockouts within the permease operon. Interruption of the distal mptD gene, which encodes the IID subunit of EII(t)(Man), strikingly led to resistance to mesentericin Y105. Moreover, MptD appears to be a peculiar membrane subunit, bearing an additional domain compared to most known IID subunits. According to these results, EII(t)(Man) is clearly involved in susceptibility to mesentericin Y105 and could even be its receptor at the E. faecalis surface. Finally, it is hypothesized that MptD could be responsible for the targeting specificity, via an interaction between its additional domain and mesentericin Y105.

The rpoN gene of Enterococcus faecalis directs sensitivity to subclass IIa bacteriocins

The final sigma 54 factor has been previously described to be involved in Listeria monocytogenes sensitivity to mesentericin Y105, a subclass IIa bacteriocin. Here, we identified the rpoN gene, encoding final sigma 54, of Enterococcus faecalis JH2-2 and showed that its interruption leads to E. faecalis resistance to different subclass IIa bacteriocins. Moreover, this rpoN mutant remained sensitive to nisin, a class I bacteriocin, suggesting that final sigma 54 is especially involved in sensitivity to subclass IIa bacteriocins.