Rôles du chimiotactisme et de la mobilité flagellaire dans la fitness des Xanthomonas

Xanthomonads are responsible for plant diseases such as black rot of Brassicaceae caused by X. campestris pv. campestris (Xcc). During the early stages of the infection, pathogenic bacteria such as Xcc must detect favorable sites and ingress into host plant tissues to colonize and multiply in the apoplast or the xylem vessels. Chemotaxis is the mechanism used by bacteria to detect attractants and repellents and adapt in consequence its direction. The aim of this work is to understand the roles of chemotaxis and flagellar motility in the fitness of xanthomonads. We showed that flagellar motility is not a general feature of xanthomonads. About 5 % of tested strains lost this ability without major impact on their fitness in planta. A chemotaxis sensor, named Hsb1, probably acquired by horizontal transfer shows a group of alleles that are specific of X. campestris. In Xcc ATCC 33913, a mutation in hsb1 resulted in a decreased penetration of this strain in the host plant tissues combined with an increase penetration in the non-host plant tissues. Hsb1 sense a signal from wounds of cabbage leaves. In vitro, a glucosinolate, the sinigrin, and an amino acid, the L-phenylalanine are detected by Hsb1 but are not metabolized. Further work is needed to identify the signal detected by the sensor and to design control methods based on confusion.Les bactéries du genre xanthomonas sont responsables de nombreuses maladies des plantes, telles que la nervation noire des brassicacées causée par x. campestris pv. campestris (xcc). Lors des phases précoces du processus infectieux, ces bactéries doivent identifier des sites favorables à leur pénétration dans les tissus et les atteindre afin de s'internaliser dans les tissus végétaux et s’y multiplier. Le chimiotactisme est le mécanisme par lequel les bactéries détectent des signaux et se dirigent vers des attractants ou s’éloignent de signaux répulsifs. L’objectif de ce travail est de comprendre les rôles du chimiotactisme et de la mobilité flagellaire dans la fitness des xanthomonas. Nous avons montré que la mobilité flagellaire n’est pas une caractéristique partagée par tous les xanthomonas mais qu’environ 5% des souches perdent cette capacité sans altération majeure de leur fitness in planta. Un senseur du chimiotactisme, dénommé hsb1, probablement acquis par transfert horizontal, présente un groupe d’allèles spécifique à x. campestris. Une mutation de hsb1 dans la souche xcc atcc 33913 entraine une diminution de l’internalisation de cette souche dans les tissus de plantes hôtes combinée à une augmentation de l’internalisation dans les tissus des plantes non-hôtes. Hsb1 perçoit un signal émis par les blessures des feuilles de chou. Un glucosinolate, la sinigrine, et un acide aminé, la l-phénylalanine, sont détectés in vitro par ce senseur, mais ne sont pas métabolisés. Des travaux complémentaires seront nécessaires pour identifier le signal détecté par ce senseur et envisager la conception de méthodes de lutte basées sur la confusion d’informations

Genome sequencing of Xanthomonas axonopodis pv. phaseoli CFBP4834-R reveals that flagellar motility is not a general feature of xanthomonads.

Xanthomonads are plant-associated bacteria that establish neutral, commensal or pathogenic relationships with plants. The list of common characteristics shared by all members of the genus Xanthomonas is now well established based on the entire genome sequences that are currently available and that represent various species, numerous pathovars of X. axonopodis (sensu Vauterin et al., 2000), X. oryzae and X. campestris, and many strains within some pathovars. These ?-proteobacteria are motile by a single polar flagellum. Motility is an important feature involved in biofilm formation, plant colonization and hence considered as a pathogenicity factor. X. axonopodis pv. phaseoli var. fuscans (Xapf) is one of the causal agents of common bacterial blight of bean and 4834-R is a highly aggressive strain of this pathogen that was isolated from a seed-borne epidemic in France in 1998. We obtained a high quality assembled sequence of the genome of this strain with 454-Solexa and 2X Sanger sequencing. Housekeeping functions are conserved in this genome that shares core characteristics with genomes of other xanthomonads: the six secretion systems which have been described so far in Gram negative bacteria are all present, as well as their ubiquitous substrates or effectors and a rather usual number of mobile elements. Elements devoted to the adaptation to the environment constitute an important part of the genome with a chemotaxis island and dispersed MCPs, numerous two-component systems, and numerous TonB dependent transporters. Furthermore, numerous multidrug efflux systems and functions dedicated to biofilm formation that confer resistance to stresses are also present. An intriguing feature revealed by genome analysis is a long deletion of 35 genes (33 kbp) involved in flagellar biosynthesis. This deletion is replaced by an insertion sequence called ISXapf2. Genes such as flgB to flgL and fliC to fleQ which are involved in the flagellar structure (rod, P- and L-ring, hook, cap and filament) are absent in the genome of strain 4834-R that is not motile. Primers were designed to detect this deletion by PCR in a collection of more than 300 strains representing different species and pathovars of Xanthomonas, and less than 5% of the tested xanthomonads strains were found nonmotile because of a deletion in the flagellum gene cluster. We observed that half of the Xapf strains isolated from the same epidemic than strain 4834-R was non-motile and that this ratio was conserved in the strains colonizing the next bean seed generation. Isolation of such variants in a natural epidemic reveals that either flagellar motility is not a key function for fitness or that some complementation occurs within the bacterial population. (Résumé d'auteur

Genome sequence of Xanthomonas fuscans subsp. fuscans strain 4834-R reveals that flagellar motility is not a general feature of xanthomonads

Abstract\ud \ud \ud \ud Background\ud Xanthomonads are plant-associated bacteria responsible for diseases on economically important crops. Xanthomonas fuscans subsp. fuscans (Xff) is one of the causal agents of common bacterial blight of bean. In this study, the complete genome sequence of strain Xff 4834-R was determined and compared to other Xanthomonas genome sequences.\ud \ud \ud \ud Results\ud Comparative genomics analyses revealed core characteristics shared between Xff 4834-R and other xanthomonads including chemotaxis elements, two-component systems, TonB-dependent transporters, secretion systems (from T1SS to T6SS) and multiple effectors. For instance a repertoire of 29 Type 3 Effectors (T3Es) with two Transcription Activator-Like Effectors was predicted. Mobile elements were associated with major modifications in the genome structure and gene content in comparison to other Xanthomonas genomes. Notably, a deletion of 33 kbp affects flagellum biosynthesis in Xff 4834-R. The presence of a complete flagellar cluster was assessed in a collection of more than 300 strains representing different species and pathovars of Xanthomonas. Five percent of the tested strains presented a deletion in the flagellar cluster and were non-motile. Moreover, half of the Xff strains isolated from the same epidemic than 4834-R was non-motile and this ratio was conserved in the strains colonizing the next bean seed generations.\ud \ud \ud \ud Conclusions\ud This work describes the first genome of a Xanthomonas strain pathogenic on bean and reports the existence of non-motile xanthomonads belonging to different species and pathovars. Isolation of such Xff variants from a natural epidemic may suggest that flagellar motility is not a key function for in planta fitness.AI is funded by a PhD grant from INRA-SPE and region Pays de la Loire, France. EG was funded by a PhD grant from the French Ministry of National Education and Research and French Guyana. SC, EG, MA, EL and LDN are funded by the LABEX TULIP (ANR-10-LABX-41), LSG is funded by ANR-2010-GENM-013 Xanthomix

Roles of chemotaxis and flagellar motility in fitness of xanthomonads

Les bactéries du genre xanthomonas sont responsables de nombreuses maladies des plantes, telles que la nervation noire des brassicacées causée par x. campestris pv. campestris (xcc). Lors des phases précoces du processus infectieux, ces bactéries doivent identifier des sites favorables à leur pénétration dans les tissus et les atteindre afin de s'internaliser dans les tissus végétaux et s’y multiplier. Le chimiotactisme est le mécanisme par lequel les bactéries détectent des signaux et se dirigent vers des attractants ou s’éloignent de signaux répulsifs. L’objectif de ce travail est de comprendre les rôles du chimiotactisme et de la mobilité flagellaire dans la fitness des xanthomonas. Nous avons montré que la mobilité flagellaire n’est pas une caractéristique partagée par tous les xanthomonas mais qu’environ 5% des souches perdent cette capacité sans altération majeure de leur fitness in planta. Un senseur du chimiotactisme, dénommé hsb1, probablement acquis par transfert horizontal, présente un groupe d’allèles spécifique à x. campestris. Une mutation de hsb1 dans la souche xcc atcc 33913 entraine une diminution de l’internalisation de cette souche dans les tissus de plantes hôtes combinée à une augmentation de l’internalisation dans les tissus des plantes non-hôtes. Hsb1 perçoit un signal émis par les blessures des feuilles de chou. Un glucosinolate, la sinigrine, et un acide aminé, la l-phénylalanine, sont détectés in vitro par ce senseur, mais ne sont pas métabolisés. Des travaux complémentaires seront nécessaires pour identifier le signal détecté par ce senseur et envisager la conception de méthodes de lutte basées sur la confusion d’informations.Xanthomonads are responsible for plant diseases such as black rot of Brassicaceae caused by X. campestris pv. campestris (Xcc). During the early stages of the infection, pathogenic bacteria such as Xcc must detect favorable sites and ingress into host plant tissues to colonize and multiply in the apoplast or the xylem vessels. Chemotaxis is the mechanism used by bacteria to detect attractants and repellents and adapt in consequence its direction. The aim of this work is to understand the roles of chemotaxis and flagellar motility in the fitness of xanthomonads. We showed that flagellar motility is not a general feature of xanthomonads. About 5 % of tested strains lost this ability without major impact on their fitness in planta. A chemotaxis sensor, named Hsb1, probably acquired by horizontal transfer shows a group of alleles that are specific of X. campestris. In Xcc ATCC 33913, a mutation in hsb1 resulted in a decreased penetration of this strain in the host plant tissues combined with an increase penetration in the non-host plant tissues. Hsb1 sense a signal from wounds of cabbage leaves. In vitro, a glucosinolate, the sinigrin, and an amino acid, the L-phenylalanine are detected by Hsb1 but are not metabolized. Further work is needed to identify the signal detected by the sensor and to design control methods based on confusion

Genome sequence of Xanthomonas fuscans subsp. fuscans strain 4834-R reveals that flagellar motility is not a general feature of xanthomonads

Abstract Background Xanthomonads are plant-associated bacteria responsible for diseases on economically important crops. Xanthomonas fuscans subsp. fuscans (Xff) is one of the causal agents of common bacterial blight of bean. In this study, the complete genome sequence of strain Xff 4834-R was determined and compared to other Xanthomonas genome sequences. Results Comparative genomics analyses revealed core characteristics shared between Xff 4834-R and other xanthomonads including chemotaxis elements, two-component systems, TonB-dependent transporters, secretion systems (from T1SS to T6SS) and multiple effectors. For instance a repertoire of 29 Type 3 Effectors (T3Es) with two Transcription Activator-Like Effectors was predicted. Mobile elements were associated with major modifications in the genome structure and gene content in comparison to other Xanthomonas genomes. Notably, a deletion of 33 kbp affects flagellum biosynthesis in Xff 4834-R. The presence of a complete flagellar cluster was assessed in a collection of more than 300 strains representing different species and pathovars of Xanthomonas. Five percent of the tested strains presented a deletion in the flagellar cluster and were non-motile. Moreover, half of the Xff strains isolated from the same epidemic than 4834-R was non-motile and this ratio was conserved in the strains colonizing the next bean seed generations. Conclusions This work describes the first genome of a Xanthomonas strain pathogenic on bean and reports the existence of non-motile xanthomonads belonging to different species and pathovars. Isolation of such Xff variants from a natural epidemic may suggest that flagellar motility is not a key function for in planta fitness

SuperB Progress Reports -- Physics

SuperB is a high luminosity e+e- collider that will be able to indirectly probe new physics at energy scales far beyond the reach of any man made accelerator planned or in existence. Just as detailed understanding of the Standard Model of particle physics was developed from stringent constraints imposed by flavour changing processes between quarks, the detailed structure of any new physics is severely constrained by flavour processes. In order to elucidate this structure it is necessary to perform a number of complementary studies of a set of golden channels. With these measurements in hand, the pattern of deviations from the Standard Model behavior can be used as a test of the structure of new physics. If new physics is found at the LHC, then the many golden measurements from SuperB will help decode the subtle nature of the new physics. However if no new particles are found at the LHC, SuperB will be able to search for new physics at energy scales up to 10-100 TeV. In either scenario, flavour physics measurements that can be made at SuperB play a pivotal role in understanding the nature of physics beyond the Standard Model. Examples for using the interplay between measurements to discriminate New Physics models are discussed in this document. SuperB is a Super Flavour Factory, in addition to studying large samples of B_{u,d,s}, D and tau decays, SuperB has a broad physics programme that includes spectroscopy both in terms of the Standard Model and exotica, and precision measurements of sin^2theta_W. In addition to performing CP violation measurements at the Y(4S) and phi(3770), SuperB will test CPT in these systems, and lepton universality in a number of different processes. The multitude of rare decay measurements possible at SuperB can be used to constrain scenarios of physics beyond the Standard Model

SuperB Progress Reports - Physics

SuperB is a high luminosity e+e- collider that will be able to indirectly probe new physics at energy scales far beyond the reach of any man made accelerator planned or in existence. Just as detailed understanding of the Standard Model of particle physics was developed from stringent constraints imposed by flavour changing processes between quarks, the detailed structure of any new physics is severely constrained by flavour processes. In order to elucidate this structure it is necessary to perform a number of complementary studies of a set of golden channels. With these measurements in hand, the pattern of deviations from the Standard Model behavior can be used as a test of the structure of new physics. If new physics is found at the LHC, then the many golden measurements from SuperB will help decode the subtle nature of the new physics. However if no new particles are found at the LHC, SuperB will be able to search for new physics at energy scales up to 10-100 TeV. In either scenario, flavour physics measurements that can be made at SuperB play a pivotal role in understanding the nature of physics beyond the Standard Model. Examples for using the interplay between measurements to discriminate New Physics models are discussed in this document. SuperB is a Super Flavour Factory, in addition to studying large samples of B_{u,d,s}, D and tau decays, SuperB has a broad physics programme that includes spectroscopy both in terms of t he Standard Model and exotica, and precision measurements of sin^2theta_W. In addition to performing CP violation measurements at the Y(4S) and phi(3770), SuperB will test CPT in these systems, and lepton universality in a number of different processes. The multitude of rare decay measurements possible at SuperB can be used to constrain scenarios of physics beyond the Standard Model. ..