Life on Arginine for Mycoplasma hominis: Clues from Its Minimal Genome and Comparison with Other Human Urogenital Mycoplasmas

Mycoplasma hominis is an opportunistic human mycoplasma. Two other pathogenic human species, M. genitalium and Ureaplasma parvum, reside within the same natural niche as M. hominis: the urogenital tract. These three species have overlapping, but distinct, pathogenic roles. They have minimal genomes and, thus, reduced metabolic capabilities characterized by distinct energy-generating pathways. Analysis of the M. hominis PG21 genome sequence revealed that it is the second smallest genome among self-replicating free living organisms (665,445 bp, 537 coding sequences (CDSs)). Five clusters of genes were predicted to have undergone horizontal gene transfer (HGT) between M. hominis and the phylogenetically distant U. parvum species. We reconstructed M. hominis metabolic pathways from the predicted genes, with particular emphasis on energy-generating pathways. The Embden–Meyerhoff–Parnas pathway was incomplete, with a single enzyme absent. We identified the three proteins constituting the arginine dihydrolase pathway. This pathway was found essential to promote growth in vivo. The predicted presence of dimethylarginine dimethylaminohydrolase suggested that arginine catabolism is more complex than initially described. This enzyme may have been acquired by HGT from non-mollicute bacteria. Comparison of the three minimal mollicute genomes showed that 247 CDSs were common to all three genomes, whereas 220 CDSs were specific to M. hominis, 172 CDSs were specific to M. genitalium, and 280 CDSs were specific to U. parvum. Within these species-specific genes, two major sets of genes could be identified: one including genes involved in various energy-generating pathways, depending on the energy source used (glucose, urea, or arginine) and another involved in cytadherence and virulence. Therefore, a minimal mycoplasma cell, not including cytadherence and virulence-related genes, could be envisaged containing a core genome (247 genes), plus a set of genes required for providing energy. For M. hominis, this set would include 247+9 genes, resulting in a theoretical minimal genome of 256 genes

Interactions peptaïbols/plantes (étude de l'effet de l'alaméthicine, toxine ou éliciteur de réactions de défense, chez la plante modèle Arabidopsis thaliana)

Les peptaïbols sont des peptides hélicoïdaux amphipathiques d'origine fongique connus pour former des pores permettant le passage des ions dans les membranes plasmiques. Des travaux récents ont mis en évidence leurs propriétés élicitrices sur certains végétaux. Nous avons étudié l'effet du peptaïbol alaméthicine sur Arabidopsis thaliana. Ce peptide induit à concentration modérée des réponses physiologiques ayant des traits communs avec la réponse hypersensible végétale. A forte concentration, la molécule est toxique et induit rapidement un clivage caractéristique des ARN ribosomiques. Les propriétés de l'alaméthicine in planta sont vraisemblablement liées à son interaction avec la membrane plasmique, la présence d'acide a-aminoisobutyrique dans sa séquence et sa résistance aux protéases végétales. L'utilisation d'un analogue fluorescent de l'alaméthicine permet d'envisager l'existence d'une cible intracellulaire secondaire.Peptaibols are helicoidal amphipathic peptides produced by soil fungi. They form pores allowing the passage of ions through plasmic membranes. Recent work highlighted their elicitor properties in plants. We studied the effect of the peptaibol alamethicin on Arabidopsis thaliana. Moderate concentrations of alamethicin induce physiological effects belonging to the plant hypersensitive response. Higher concentrations are toxic and quickly induce a characteristic ribosomal RNA cleavage. The properties of alamethicin in plants are probably related to its interaction with the plasmic membrane, to the presence of a-aminoisobutyric acid in its sequence and to its resistance to plant proteases. The use of a fluorescent analogue of alamethicin might suggest the existence of a secondary intracellular target.COMPIEGNE-BU (601592101) / SudocSudocFranceF

Evaluation d’un moyen de bio-contrôle innovant vis-à-vis des bactérioses : les peptides antimicrobiens, de la recherche fondamentale à la pratique.

Les bactéries phytopathogènes représentent de redoutables ennemis pour différentes cultures telles queles cultures de kiwi, de melon, de noyer, ou encore de laitue avec des retombés d’importanceéconomique. La difficulté de gestion des maladies bactériennes provient du fait (i) de la complexité del’agent pathogène (capacité d’évolution, épidémiologie, …) et (ii) de l’absence de moyen de lutte curatif.Le principal produit utilisable en agriculture est le cuivre pour son activité uniquement préventive mais quine permet pas de venir à bout des fortes épidémies sévissant ces dernières années.Un moyen de protection développé depuis de nombreuses années dans le domaine médical notammentpour lutter contre l’apparition des résistances aux antibiotiques dans les hôpitaux, commence à faire sonapparition dans le domaine agricole : l’utilisation des peptides antimicrobiens (PAMs). D’origine naturelleou de synthèse, les PAMs, petites molécules de moins de 50 acides aminés, ont une activité bactéricide.L’objectif de ce projet était d’évaluer l’efficacité d’une gamme de PAMs vis-à-vis des bactériesphytopathogènes ainsi que leurs possibles applications en protection des plantes. La preuve de conceptest aujourd’hui faite : les PAMs évalués dans ce projet sont efficaces en conditions contrôlées sur unelarge gamme de souches bactériennes appartenant aux genres Pseudomonas et Xanthomonas.Cependant, il existe deux principaux freins au développement de ce type de produits dans le domaineagricole : (i) le coût de production de ces produits à la fois d’origine naturelle mais plus encore pour cellesynthétique, et (ii) le faible développement de produits concentrés en PAMs des professionnels del’agrochimiePhytopathogenic bacteria are severe enemies on various crops of economic importance such as kiwi,melon, walnut, or lettuce. The difficulty of managing bacterial diseases is due to 1) the complexity of thepathogens (evolutionary capacity, epidemiology, ...) and 2) the lack of curative control. The main productthat can be used in agriculture is copper, which has only a preventive activity and does not overcome thestrong epidemics that have been occurring in recent years.A means of protection has been developed for many years in the medical field and is beginning to appearin the agricultural field: the use of antimicrobial peptides (PAMs), small molecules of less than 50 aminoacids with bactericidal activity. Of natural or synthetic origin, PAMs are developed to fight against theemergence of antibiotic resistance in hospitals.The objective of this project was to evaluate the effectiveness of a range of PAMs against phytopathogenicbacteria and to evaluate their possible uses in plant protection. The proof of concept is now done: the PAMs evaluated in this project are effective under controlled conditions against a wide range of bacterialstrains belonging to the genera Pseudomonas and Xanthomonas.However, there are two main obstacles to the development of this type of products in the agricultural field:1) the production cost of these products, whether they are of natural origin or synthetic, and 2) the fewproducts concentrated in PAMs being developed by agrochemical companies

Caractérisation de l'interaction de l'ampullosporine A avec différents environnements membranaires (relation séquence-activité in planta de peptaïbols naturels ou synthétiques)

COMPIEGNE-BU (601592101) / SudocSudocFranceF

Comparison of Current Methods for Signal Peptide Prediction in Phytoplasmas

Although phytoplasma studies are still hampered by the lack of axenic cultivation methods, the availability of genome sequences allowed dramatic advances in the characterization of the virulence mechanisms deployed by phytoplasmas, and highlighted the detection of signal peptides as a crucial step to identify effectors secreted by phytoplasmas. However, various signal peptide prediction methods have been used to mine phytoplasma genomes, and no general evaluation of these methods is available so far for phytoplasma sequences. In this work, we compared the prediction performance of SignalP versions 3.0, 4.0, 4.1, 5.0 and Phobius on several sequence datasets originating from all deposited phytoplasma sequences. SignalP 4.1 with specific parameters showed the most exhaustive and consistent prediction ability. However, the configuration of SignalP 4.1 for increased sensitivity induced a much higher rate of false positives on transmembrane domains located at N-terminus. Moreover, sensitive signal peptide predictions could similarly be achieved by the transmembrane domain prediction ability of TMHMM and Phobius, due to the relatedness between signal peptides and transmembrane regions. Beyond the results presented herein, the datasets assembled in this study form a valuable benchmark to compare and evaluate signal peptide predictors in a field where experimental evidence of secretion is scarce. Additionally, this study illustrates the utility of comparative genomics to strengthen confidence in bioinformatic predictions

The Peptaibol Alamethicin induces an rRNA-Cleavage-Associated death in Arabidopsis thaliana

International audienceThe plant-metabolic response to amphipathic peptides produced by the soil fungi of the genus Trichoderma remains largely unknown. The present investigation was undertaken to examine the death process in alamethicin-treated Arabidopsis thaliana plantlets. The rapid death triggered by alamethicin (at 50 μM) was shown to be associated with protein-synthesis arrest and with specific cleavage of 18S and 25S ribosomal RNA. The use of an inhibitor of nitric oxide (NO) synthases and of an NO scavenger suggested that rRNA cleavage was suppressed by NO. Experiments conducted with a synthetic alamethicin analogue, in which all α-aminoisobutyric acid (Aib) residues have been replaced by leucine moieties, showed that the non-coded residues are essential for the ability of the peptaibol to induce rRNA cleavage in Arabidopsis. Our data indicate that further investigations on the mode of action of alamethicin in planta could be of great interest to study the death-signaling pathway associated with rRNA degradation in plants

Genetic diversity of strains of Spiroplasma citri isolated in southern Iran

Spiroplasma citri, the causal agent of citrus stubborn disease, is widely distributed in citrus groves and causes heavy losses to the citrus industry in southern Iran. In the present study the genetic diversity of S. citri strains isolated from various hosts and locations in the Fars Province in southern Iran was investigated. The bacterium was cultured from stubborn affected citrus trees, sesame and safflower plants, and leafhopper vector Circulifer haematoceps. Based on PCR-RFLP of the spiralin gene (spi), four groups could be clearly identified among Iranian S. citri isolates. Group 1 was prominent with 71.8% of isolates found in both citrus and non-citrus hosts. Members of groups 2 (18%), and 5 (5.1%) were identified only in citrus, and members of group 6 only in non-citrus hosts. Phylogenetic analyses based on spi gene sequence could not clearly discriminate isolates of groups 1 and 2. In most cases, RAPD-PCR allowed the differentiation of isolates in different clades based on location or host. However there was no correlation between classification based on RFLP of spi gene and RAPD-PCR of whole genome. Finally, the study was completed by the demonstration that Iranian isolates found only in non-citrus hosts (group 6) including insect vectors are capable of infecting key lime when experimentally transmitted to the plant via a dodder bridge

One step generation of single-core double emulsions from polymer-osmose-induced aqueous phase separation in polar oil droplets

Water-in-oil-in-water emulsions (W/O/W) are aqueous droplet(s) embedded within oil droplets dispersed in a continuous water phase. They are attracting interest due to their possible applications from cosmetic to food science since both hydrosoluble and liposoluble cargos can be encapsulated within. They are generally prepared using a one-step or a two-step method, phase inversion and also via spontaneous emulsification. Here, we describe a general and simple one-step method based on hydrophilic polymers dispersed in polar oils to generate osmose-induced diffusion of water into oil droplets, forming polymer-rich aqueous droplets inside the oil droplets. Polyethylene glycol, but also other hydrophilic polymers (branched polyethylene imine or polyvinyl pyrrolidone) were successfully dispersed in 1-octanol or other polar oils (oleic acid or tributyrin) to produce an O/W emulsion that spontaneously transformed into a W1/O/W2 emulsion, with the inner aqueous droplet (W1) only containing the hydrophilic polymer initially dispersed in oil. By combining single drop experiments, with macroscopic viscosity measurements, we demonstrated that the double emulsion resulted of water diffusion, which amplitude could be adjusted by the polymer concentration. The production of high internal phase emulsions was also achieved, together with a pH-induced transition from multiple to single core double emulsion. We expect this new method for producing double emulsions to find applications in domains of microencapsulation and materials chemistr