Evolution Of Host-pathogen Interactions Research Articles

Characterization of a potential Escherichia coli virulence factor identified in a screen using the social amoeba phagocyte, Dictyostelium discoideum

Abstract Escherichia coli are a typical component of mammalian gut microbiota; however, a number of pathogenic strains remain a health challenge for developing countries. To identify novel bacterial virulence factors, we used the social amoeba, Dictyostelium discoideum, which preys upon soil bacteria, including E. coli, as a model for mammalian phagocytic cells. Using random mutagenesis, screening for mutant E. coli strains resistant to killing upon phagocytosis, and genomic sequencing of these resistant strains, we identified mutations in several potential genes of interest, including an E. coli gene of unknown function, yfaT. Preliminary results suggest that D. discoideum Erk signaling is reduced in response to yfaT-deficient E. coli. Furthermore, mammalian TLR4 signaling in response to yfaT-deficient E. coli also appears attenuated. Our current studies focus on characterizing differences in growth patterns for wild-type and yfaT-deficient E. coli using Biolog screenings, as well as analyzing potential differences in LPS structure in these strains. These studies are aimed at identification and characterization of novel mechanisms that may be involved in bacterial virulence. In addition, given that the development of mechanisms to resist D. discoideum predation may have contributed to the selection and maintenance of bacterial virulence factors, such as yfaT, against mammalian hosts, these studies may provide insight on the evolution of host-pathogen interactions.

MIGREW: database on molecular identification of genes for resistance in wheat

Population structure of fungal infections in wheat differs between wheat varieties and environments. Taking into account evolution of host-pathogen interactions, genetic diversity of both wheat and fungus must be a monitored. In order to catalogue information to support need of wheat pathologists and breeders, who use conventional methods and Molecular Assisted Selection (MAS) techniques, we have developed the Molecular Identification of Genes for Resistance in Wheat (MIGREW) database. The main goal of this database is to support wheat breeding efforts to develop immunity to rusts and powdery mildew. MIGREW is also focused on effectiveness of wheat resistance genes in different regions of Russia to provide users relevant information on the rapidly changing population structure of pathogens.

Identification of Virulence and Virulence Regulatory Factors in Escherichia coli using Dictyostelium discoideum as a Model Phagocyte

Abstract Escherichia coli is normally found as part of the human gut microbiota, however there exist a number of diarrheagenic strains. Identification and disruption of the virulence factors that promote infection could lead to a reduction in infection period of these E. coli strains and potentially of other species with similar means of virulence. To identify E. coli strains with altered virulence, we used Dictyostelium discoideum, a social amoeba that phagocytizes bacteria for nutritional purposes. Using random mutagenesis, we created mutant stocks of E. coli, each. These stocks were subjected to several rounds of phagocytosis by D. discoideum, enriching the culture and selecting for mutants resistant to intracellular killing. Resistant mutants were isolated and we found that some of the resistant strains showed increased survival when compared to the wild-type strain. Once isolated, the full genomes of our resistant mutant strains were sequenced using Illumina’s next generation MiSeq technology. While analyzing the sequencing data from these mutant strains, we found several potential genes of interest, including genes related to flagella, oxidoreductases, and acid resistance. We have begun to characterize genes of interest through various qualitative and quantitative assays using individual gene knockout strains. These studies should allow for identification of novel factors associated with regulation of virulence in E. coli. In addition, given that the development of mechanisms to resist D. discoideum predation may have contributed to the selection and maintenance of bacterial virulence factors against mammalian hosts, these studies may provide insight on the evolution of host-pathogen interactions.

Development of Dictyostelium discoideum as a model to identify evolutionarily-conserved virulence factors in Escherichia coli

Abstract Escherichia coli are a typical component of mammalian gut microbiota; however, a number of pathogenic strains remain a health concern for developing countries. Identification and disruption of virulence factors that promote infection could lead to reduction in infection. To identify novel bacterial virulence factors, we are using the soil amoeba, Dictyostelium discoideum, which preys upon bacteria, including E. coli, in the soil, as a model for mammalian phagocytic cells. Using random mutagenesis, we have created mutant stocks of MG1655 E. coli. These stocks were fed to D. discoideum, enriching the culture and selecting for mutants that were resistant to killing upon phagocytosis. After several rounds of selection, resistant mutant strains were isolated, and we found that some strains showed up to 100-fold increase in survival over a 2 h period. Once isolated, the genomes of the resistant mutant strains were sequenced and the sequences compared to that of the initial WT strain using Illumina’s MiSeq technology. While analyzing the sequences from these mutant strains, we found mutations in several potential genes of interest and are working to characterize their roles in the cell. We are testing E. coli strains reconstituted with specific mutations to identify particular mutations that are associated with phagocytosis-resistant phenotypes. These studies are aimed at identifying particular bacterial genes that may be involved in regulation of virulence. In addition, given that the development of mechanisms to resist D. discoideum predation may have contributed to the selection and maintenance of bacterial virulence factors against mammalian hosts, these studies may provide insight on the evolution of host-pathogen interactions.

Horizontal transfer and the evolution of host-pathogen interactions.

Horizontal gene transfer has been long known in viruses and prokaryotes, but its importance in eukaryotes has been only acknowledged recently. Close contact between organisms, as it occurs between pathogens and their hosts, facilitates the occurrence of DNA transfer events. Once inserted in a foreign genome, DNA sequences have sometimes been coopted by pathogens to improve their survival or infectivity, or by hosts to protect themselves against the harm of pathogens. Hence, horizontal transfer constitutes a source of novel sequences that can be adopted to change the host-pathogen interactions. Therefore, horizontal transfer can have an important impact on the coevolution of pathogens and their hosts.