RESUMO
Members of the genus Xenorhabdus are entomopathogenic bacteria that associate with nematodes. The nematode-bacteria pair infects and kills insects, with both partners contributing to insect pathogenesis and the bacteria providing nutrition to the nematode from available insect-derived nutrients. The nematode provides the bacteria with protection from predators, access to nutrients, and a mechanism of dispersal. Members of the bacterial genus Photorhabdus also associate with nematodes to kill insects, and both genera of bacteria provide similar services to their different nematode hosts through unique physiological and metabolic mechanisms. We posited that these differences would be reflected in their respective genomes. To test this, we sequenced to completion the genomes of Xenorhabdus nematophila ATCC 19061 and Xenorhabdus bovienii SS-2004. As expected, both Xenorhabdus genomes encode many anti-insecticidal compounds, commensurate with their entomopathogenic lifestyle. Despite the similarities in lifestyle between Xenorhabdus and Photorhabdus bacteria, a comparative analysis of the Xenorhabdus, Photorhabdus luminescens, and P. asymbiotica genomes suggests genomic divergence. These findings indicate that evolutionary changes shaped by symbiotic interactions can follow different routes to achieve similar end points.
Assuntos
Variação Genética , Genoma Bacteriano/genética , Photorhabdus/genética , Xenorhabdus/genética , Animais , Cromossomos Bacterianos/genética , DNA Bacteriano/química , DNA Bacteriano/genética , Enterobacteriaceae/classificação , Enterobacteriaceae/genética , Enterobacteriaceae/fisiologia , Genômica/métodos , Interações Hospedeiro-Parasita , Interações Hospedeiro-Patógeno , Insetos/microbiologia , Insetos/parasitologia , Dados de Sequência Molecular , Nematoides/microbiologia , Nematoides/fisiologia , Photorhabdus/classificação , Photorhabdus/fisiologia , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Especificidade da Espécie , Simbiose , Xenorhabdus/classificação , Xenorhabdus/fisiologiaRESUMO
Virulence of the insect pathogen Xenorhabdus nematophila is attributed in part to its ability to suppress immunity. For example, X. nematophila suppresses transcripts encoding several antimicrobial proteins, even in the presence of Salmonella enterica, an inducer of these transcripts. We show here that virulence and immune suppression phenotypes can be lost in a subpopulation of X. nematophila. Cells that have undergone 'virulence modulation' (vmo) have attenuated virulence and fail to suppress antimicrobial transcript levels, haemocyte aggregation and nodulation in Manduca sexta insects. When plated on certain media, vmo cells have a higher proportion of translucent (versus opaque) colonies compared with non-vmo cells. Like vmo strains, translucent colony isolates are defective in virulence and immune suppression. The X. nematophila genome encodes two 'opacity' genes with similarity to the Ail/PagC/Rck family of outer membrane proteins involved in adherence, invasion and serum resistance. Quantitative polymerase chain reaction analysis shows that RNA levels of one of these opacity genes, opaB, are higher in opaque relative to translucent colonies. We propose that in X. nematophila opaB may be one of several factors involved in immune suppression during infection, and expression of these factors can be co-ordinately eliminated in a subpopulation, possibly through a phase variation mechanism.
Assuntos
Manduca/imunologia , Xenorhabdus/patogenicidade , Animais , Northern Blotting , Hemócitos/citologia , Hemócitos/imunologia , Hemócitos/microbiologia , Larva/imunologia , Larva/microbiologia , Manduca/microbiologia , Virulência/genética , Fatores de Virulência/genética , Fatores de Virulência/fisiologia , Xenorhabdus/genéticaRESUMO
This study determined the phylogenetic groups and virulence factors of 37 Escherichia coli isolates producing types of CTX-M compared with those of 19 isolates producing different types of extended-spectrum beta-lactamases (ESBLs) in a well-defined North American population. Most CTX-M-14 producers (97%) were from phylogenic group D; 67% of the CTX-M-15 producers were from group B2. A single CTX-M-14-producing strain belonged to clonal group A. There were significant prevalence differences for individual virulence factors among CTX-M producers and nonproducers; however, aggregate virulence factor scores were similar. CTX-M producers more commonly caused repeat urinary tract infections. Our results indicate that CTX-M type predicts phylogenetic background, and the virulence potential of ESBL-producing E. coli isolates is a complex issue, requiring further study and ongoing surveillance.
Assuntos
Escherichia coli/patogenicidade , Fatores de Virulência/análise , beta-Lactamases/biossíntese , Escherichia coli/classificação , Escherichia coli/enzimologia , Humanos , FilogeniaRESUMO
An insertion between iscA and hscB of the Xenorhabdus nematophila iscRSUA-hscBA-fdx locus, predicted to encode Fe-S assembly machinery, prevented colonization of Steinernema carpocapsae nematodes. The insertion disrupted cotranscription of iscA and hscB, but did not reduce hscBA expression, suggesting that X. nematophila requires coordinated expression of the isc-hsc-fdx locus for colonization.
