Salmonella virulence in animals depends on effectors injected by Type III Secretion Systems (T3SSs). In this report we demonstrate that Salmonella mutants that are unable to deliver effectors are also compromised in infection of Arabidopsis thaliana plants. Transcriptome analysis revealed that in contrast to wild type bacteria, T3SS mutants of Salmonella are compromised in suppressing highly conserved Arabidopsis genes that play a prominent role during Salmonella infection of animals. We also found that Salmonella originating from infected plants are equally virulent for human cells and mice. These results indicate a high degree of conservation in the defense and infection mechanism of animal and plant hosts during Salmonella infection.

Infections with Salmonella enterica belong to the most prominent causes of food poisoning and infected fruits and vegetables represent important vectors for salmonellosis. Recent evidence indicates that plants recognize S. enterica and raise defense responses. Nonetheless, the molecular mechanisms controlling the interaction of S. enterica with plants are still largely unclear. Here, we show that flagellin from S. enterica represents a prominent pathogen-associated molecular pattern (PAMP) in Arabidopsis thaliana, which induces PAMP-triggered immunity (PTI) via the recognition of the flg22 domain by the receptor kinase FLS2. The Arabidopsis fls2 mutant shows reduced though not abolished PTI activation, indicating that plants rely also on recognition of other S. enterica PAMPs. Interestingly, the S. enterica type III secretion system (T3SS) mutant prgH- induced stronger defense gene expression than wild-type bacteria in Arabidopsis, suggesting that T3SS effectors are involved in defense suppression. Furthermore, we observe that S. enterica strains show variation in the flg22 epitope, which results in proteins with reduced PTI-inducing activity. Altogether, these results show that S. enterica activates PTI in Arabidopsis and suggest that, in order to accomplish plant colonization, S. enterica evolved strategies to avoid or suppress PTI.

Degradation of the quorum-sensing (QS) signals known as N-acylhomoserine lactones (AHL) by soil bacteria may be useful as a beneficial trait for protecting crops, such as potato plants, against the worldwide pathogen Pectobacterium. In this work, analytical chemistry and microbial and molecular approaches were combined to explore and compare biostimulation of native and introduced AHL-degrading Rhodococcus erythropolis populations in the rhizosphere of potato plants cultivated in farm greenhouses under hydroponic conditions. We first identified gamma-heptalactone (GHL) as a novel biostimulating agent that efficiently promotes plant root colonization by AHL-degrading R. erythropolis population. We also characterized an AHLdegrading biocontrol R. erythropolis isolate, R138, which was introduced in the potato rhizosphere. Moreover, root colonization by AHL-degrading bacteria receiving different combinations of GHL and R138 treatments was compared by using a cultivationbased approach (percentage of AHL-degrading bacteria), pyrosequencing of PCR-amplified rrs loci (total bacterial community), and quantitative PCR (qPCR) of the qsdA gene, which encodes an AHL lactonase in R. erythropolis. Higher densities of the AHLdegrading R. erythropolis population in the rhizosphere were observed when GHL treatment was associated with biocontrol strain R138. Under this condition, the introduced R. erythropolis population displaced the native R. erythropolis population. Finally, chemical analyses revealed that GHL, gamma-caprolactone (GCL), and their by-products, gamma-hydroxyheptanoic acid and gamma-hydroxycaproic acid, rapidly disappeared from the rhizosphere and did not accumulate in plant tissues. This integrative study highlights biostimulation as a potential innovative approach for improving root colonization by beneficial bacteria. N-Acylhomoserine lactones are intercellular signals used by numerous alpha-, beta-, and gammaproteobacteria to regulate gene expression at the population and community levels (18,38). The mechanism connecting cell population to gene expression via AHLs is termed quorum sensing (QS) (17). Pectobacterium carotovorum is a causative agent of blackleg and soft rot diseases in several crops, including potato plants and tubers. Over the 2004-2009 period, quality refusals oscillated between 2 and 5% and 3 and 8% of the total seed tuber production in France and Netherlands, respectively; blackleg disease, which is caused by Pectobacterium and Dickeya, represented 10 to 30% and 60 to 80% of the causes of refusal in the same countries. In Pectobacterium, production of virulence factors such as pectinolytic and cellulolytic enzymes and harpins is positively controlled by AHLs (23, 29). In Pectobacterium carotovorum, inhibition of AHL synthesis or degradation of the AHLs produced results in the absence of the expression of the QS-regulated genes and consequently in a decrease of the virulence symptoms on potato plants (23,31).During the past decade, several approaches have been proposed to disrupt QS regulatio...

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New genomic sequence data were acquired for the Acipenser iridovirus-European (AcIV-E), a virus whose complete genome and classification still remain to be elucidated. Here, we obtained the first full-length Major capsid protein (MCP) gene sequence for AcIV-E, as well as two additional open reading frames (ORFs) adjacent to the MCP gene. BLAST searches of the first ORF (α) resulted in no match to any gene or protein in the public databases. The other ORF (β) was identified as a subunit of a replication factor C (RFC), known to function as a clamp loader in eukaryotes, archae and some viruses. The presence of similar RFC genes was confirmed in two distinct, yet related, viruses, the white sturgeon iridovirus and a European variant of Namao virus. The existence of an RFC gene in AcIV-E suggests a genome size larger than that of other classifiable members of the family Iridoviridae along with a mode of replication involving an interaction between a clamp loader and a proliferating nuclear cell antigen. Sequencing and comparison of the full-length RFC gene from various sturgeon samples infected with AcIV-E revealed two distinct clusters of sequences within one particular sample in which the coexistence of two lineages had previously been predicted based on analysis of the partial MCP gene sequence. These genetic data provide further evidence of the circulation of at least two concurrent AcIV-E lineages, sometimes co-infecting cultured European sturgeon.

-Sphaerothecum destruens has emerged as a serious parasite of fish. Its life cycle, as well as its association with Asian cyprinids, allows it to infect a wide range of hosts. The topmouth gudgeon (Pseudorasbora parva), an invasive species that has rapidly colonized Europe, has been shown to be a healthy carrier of the parasite. However, in France, the presence of S. destruens and its possible association with P. parva have not yet been demonstrated. Here, we screened topmouth gudgeon DNA for S. destruens using PCR amplification of an 18S rRNA gene fragment of the parasite. Sequencing and phylogenetic analysis confirmed the presence of S. destruens in the invasive fish species. Our results suggest that P. parva can be a potent vector of the parasite, and has the potential to become a major ecological and economic threat to the French fish population.Keywords: Sphaerothecum destruens / Pseudorasbora parva / invasive species / topmouth gudgeon / France Résumé -Première mise en évidence de l'association de Sphaerothecum destruens avec Pseudorasbora parva en France. Sphaerothecum destruens est apparu dans la littérature scientifique comme un redoutable parasite émergent de poissons. Son cycle de vie, ainsi que son association à un cyprinidé d'origine asiatique, lui permettent d'infecter un large spectre d'hôtes. En effet, le goujon asiatique (Pseudorasbora parva) s'est révélé être porteur sain de ce parasite dans plusieurs études et représente une des espèces invasives ayant colonisé le plus rapidement l'Europe et notamment la France. Bien que le statut de porteur sain ait été donné au goujon asiatique, à notre connaissance, aucune étude n'a été menée en France afin de démontrer cette association. Par conséquent, l'objectif de cette étude a été d'évaluer la présence de S. destruens dans ce pays et la possibilité de considérer Pseudorasbora parva comme un vecteur de la maladie. Ceci a été confirmé par amplification PCR d'un fragment du gène ARNr 18S du parasite, réalisée sur un extrait d'ADN obtenu à partir de plusieurs goujons. Un séquençage et une analyse phylogénétique ont par la suite confirmé qu'il s'agissait bien de S. destruens. Ces résultats permettent donc d'affirmer que l'espèce invasive P. parva pourrait présenter une grande menace aussi bien écologique qu'économique sur le territoire français.

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Salmonella are the causative agents of the majority of food-borne bacterial poisonings and are responsible for more than 100 million infections of humans annually. In contrast to typhoid and paratyphoid fever, salmonellosis is frequent in the developed world. This is largely contributed by changes in the nutritional behavior resulting in eating more fruits and raw vegetables. Recently, it was discovered that the colonization of plants by Salmonella is a highly organized process. These results indicate that plants form part of the natural life cycle of Salmonella and open up new strategies to understand and combat bacterial diseases.