RESUMEN
Yersinia pestis, which causes bubonic plague, forms biofilms in fleas, its insect vectors, as a means to enhance transmission. Biofilm development is positively regulated by hmsT, encoding a diguanylate cyclase that synthesizes the bacterial second messenger cyclic-di-GMP. Biofilm development is negatively regulated by the Rcs phosphorelay signal transduction system. In this study, we show that Rcs-negative regulation is accomplished by repressing transcription of hmsT.
Asunto(s)
Proteínas Bacterianas/metabolismo , Biopelículas/crecimiento & desarrollo , Regulación Bacteriana de la Expresión Génica/fisiología , Yersinia pestis/fisiología , Animales , Proteínas Bacterianas/genética , Caenorhabditis elegans/microbiología , Regulación Enzimológica de la Expresión Génica/fisiología , Regiones Promotoras Genéticas , Unión Proteica , Transducción de Señal , Transcripción Genética , Yersinia pestis/genéticaRESUMEN
Yersinia pestis, the agent of bubonic plague, evolved from the enteric pathogen Yersinia pseudotuberculosis within the past 20,000 years. Because ancestor and descendant both exist, it is possible to infer steps in molecular evolution by direct experimental approaches. The Y. pestis life cycle includes establishment of a biofilm within its vector, the flea. Although Y. pseudotuberculosis makes biofilms in other environments, it fails to do so in the insect. We show that rcsA, a negative regulator of biofilms that is functional in Y. pseudotuberculosis, is a pseudogene in Y. pestis. Replacement of the pseudogene with the functional Y. pseudotuberculosis rcsA allele strongly represses biofilm formation and essentially abolishes flea biofilms. The conversion of rcsA to a pseudogene during Y. pestis evolution, therefore, was a case of negative selection rather than neutral genetic drift.
Asunto(s)
Evolución Molecular , Seudogenes/genética , Selección Genética , Yersinia pestis/genética , Sustitución de Aminoácidos , Animales , Proteínas Bacterianas/genética , Biopelículas/crecimiento & desarrollo , Caenorhabditis elegans/microbiología , Recuento de Colonia Microbiana , Modelos Biológicos , Mutación/genética , Fenotipo , Transducción de Señal , Siphonaptera/microbiología , Yersinia pestis/citología , Yersinia pestis/crecimiento & desarrolloRESUMEN
Bubonic plague, one of history's deadliest infections, is transmitted by fleas infected with Yersinia pestis. The bacteria can starve fleas by blocking their digestive tracts, which stimulates the insects to bite repeatedly and thereby infect new hosts. Direct examination of infected fleas, aided by in vitro studies and experiments with the nematode Caenorhabditis elegans, have established that Y. pestis forms a biofilm in the insect. The extracellular matrix of the biofilm seems to contain a homopolymer of N-acetyl-d-glucosamine, which is a constituent of many bacterial biofilms. A regulatory mechanism involved in Y. pestis biofilm formation, cyclic-di-GMP signaling, is also widespread in bacteria; yet only Y. pestis forms biofilms in fleas. Here, the historical background of bubonic plague is briefly described and recent studies investigating the mechanisms by which these unique and deadly biofilms are formed are discussed.
Asunto(s)
Biopelículas/crecimiento & desarrollo , Sistema Digestivo/microbiología , Siphonaptera/microbiología , Yersinia pestis/crecimiento & desarrollo , Animales , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Caenorhabditis elegans/microbiología , Interacciones Huésped-Patógeno , Humanos , Microscopía Electrónica de Transmisión , Peste/microbiología , Peste/transmisión , Polisacáridos Bacterianos/química , Polisacáridos Bacterianos/metabolismo , Siphonaptera/ultraestructura , Yersinia pestis/genética , Yersinia pestis/ultraestructuraRESUMEN
A few Yersinia pseudotuberculosis strains form biofilms on the head of the nematode Caenorhabditis elegans, but numerous others do not. We show that a widely used Y. pseudotuberculosis strain, YPIII, is biofilm positive because of a mutation in phoP, which encodes the response regulator of a two-component system. For two wild-type Y. pseudotuberculosis that do not make biofilms on C. elegans, deletion of phoP was sufficient to produce robust biofilms. In Yersinia pestis, a phoP mutant made more extensive biofilms in vitro than did the wild type. Expression of HmsT, a diguanylate cyclase that positively regulates biofilms, is diminished in Y. pseudotuberculosis strains with functional PhoP.
Asunto(s)
Proteínas Bacterianas/farmacología , Biopelículas/efectos de los fármacos , Biopelículas/crecimiento & desarrollo , Regulación Bacteriana de la Expresión Génica , Yersinia pestis/efectos de los fármacos , Yersinia pseudotuberculosis/efectos de los fármacos , Animales , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Caenorhabditis elegans/microbiología , Proteínas de Escherichia coli , Liasas de Fósforo-Oxígeno/genética , Liasas de Fósforo-Oxígeno/metabolismo , Transducción de Señal , Yersinia pestis/enzimología , Yersinia pestis/genética , Yersinia pestis/crecimiento & desarrollo , Yersinia pseudotuberculosis/enzimología , Yersinia pseudotuberculosis/genética , Yersinia pseudotuberculosis/crecimiento & desarrolloRESUMEN
The detailed composition and structure of the Caenorhabditis elegans surface are unknown. Previous genetic studies used antibody or lectin binding to identify srf genes that play roles in surface determination. Infection by Microbacterium nematophilum identified bus (bacterially unswollen) genes that also affect surface characteristics. We report that biofilms produced by Yersinia pestis and Y. pseudotuberculosis, which bind the C. elegans surface predominantly on the head, can be used to identify additional surface-determining genes. A screen for C. elegans mutants with a biofilm absent on the head (Bah) phenotype identified three novel genes: bah-1, bah-2, and bah-3. The bah-1 and bah-2 mutants have slightly fragile cuticles but are neither Srf nor Bus, suggesting that they are specific for surface components involved in biofilm attachment. A bah-3 mutant has normal cuticle integrity, but shows a stage-specific Srf phenotype. The screen produced alleles of five known surface genes: srf-2, srf-3, bus-4, bus-12, and bus-17. For the X-linked bus-17, a paternal effect was observed in biofilm assays.
Asunto(s)
Adhesión Bacteriana/fisiología , Biopelículas , Caenorhabditis elegans/microbiología , Mutación/genética , Yersinia/fisiología , Animales , Caenorhabditis elegans/aislamiento & purificación , Proteínas de Caenorhabditis elegans/metabolismo , Epidermis/metabolismo , Locomoción , FenotipoRESUMEN
The bacterium Xenorhabdus nematophila is an insect pathogen and an obligate symbiont of the nematode Steinernema carpocapsae. X. nematophila makes a biofilm that adheres to the head of the model nematode Caenorhabditis elegans, a capability X. nematophila shares with the biofilms made by Yersinia pestis and Yersinia pseudotuberculosis. As in Yersinia spp., the X. nematophila biofilm requires a 4-gene operon, hmsHFRS. Also like its Yersinia counterparts, the X. nematophila biofilm is bound by the lectin wheat germ agglutinin, suggesting that beta-linked N-acetyl-D-glucosamine or N-acetylneuraminic acid is a component of the extracellular matrix. C. elegans mutants with aberrant surfaces that do not permit Yersinia biofilm attachment also are resistant to X. nematophila biofilms. An X. nematophila hmsH mutant that failed to make biofilms on C. elegans had no detectable defect in symbiotic association with S. carpocapsae, nor was virulence reduced against the insect Manduca sexta.
Asunto(s)
Adhesión Bacteriana , Biopelículas/crecimiento & desarrollo , Caenorhabditis elegans/microbiología , Operón , Xenorhabdus/crecimiento & desarrollo , Animales , Secuencia de Bases , Genes Bacterianos , Prueba de Complementación Genética , Manduca/microbiología , Datos de Secuencia Molecular , Mutación , Filogenia , Virulencia , Aglutininas del Germen de Trigo/metabolismo , Xenorhabdus/genética , Xenorhabdus/metabolismo , Xenorhabdus/patogenicidadRESUMEN
BACKGROUND: In sequencing the genomes of two Xenorhabdus species, we encountered a large number of sequence repeats and assembly anomalies that stalled finishing efforts. This included a stretch of about 12 Kb that is over 99.9% identical between the plasmid and chromosome of X. nematophila. RESULTS: Whole genome restriction maps of the sequenced strains were produced through optical mapping technology. These maps allowed rapid resolution of sequence assembly problems, permitted closing of the genome, and allowed correction of a large inversion in a genome assembly that we had considered finished. CONCLUSION: Our experience suggests that routine use of optical mapping in bacterial genome sequence finishing is warranted. When combined with data produced through 454 sequencing, an optical map can rapidly and inexpensively generate an ordered and oriented set of contigs to produce a nearly complete genome sequence assembly.
Asunto(s)
Genoma Bacteriano , Mapeo Restrictivo , Análisis de Secuencia de ADN/métodos , Xenorhabdus/genética , Cromosomas Bacterianos , Simulación por Computador , Mapeo Contig , Elementos Transponibles de ADN , ADN Bacteriano/genética , Procesamiento de Imagen Asistido por Computador , Plásmidos , ARN RibosómicoRESUMEN
The surface of the nematode Caenorhabditis elegans is poorly understood but critical for its interactions with the environment and with pathogens. We show here that six genes (bus-2, bus-4, and bus-12, together with the previously cloned srf-3, bus-8, and bus-17) encode proteins predicted to act in surface glycosylation, thereby affecting disease susceptibility, locomotory competence, and sexual recognition. Mutations in all six genes cause resistance to the bacterial pathogen Microbacterium nematophilum, and most of these mutations also affect bacterial adhesion and biofilm formation by Yersinia species, demonstrating that both infection and biofilm formation depend on interaction with complex surface carbohydrates. A new bacterial interaction, involving locomotory inhibition by a strain of Bacillus pumilus, reveals diversity in the surface properties of these mutants. Another biological property--contact recognition of hermaphrodites by males during mating--was also found to be impaired in mutants of all six genes. An important common feature is that all are expressed most strongly in seam cells, rather than in the main hypodermal syncytium, indicating that seam cells play the major role in secreting surface coat and consequently in determining environmental interactions. To test for possible redundancies in gene action, the 15 double mutants for this set of genes were constructed and examined, but no synthetic phenotypes were observed. Comparison of the six genes shows that each has distinctive properties, suggesting that they do not act in a linear pathway.
Asunto(s)
Adhesión Bacteriana , Proteínas de Caenorhabditis elegans/genética , Caenorhabditis elegans/citología , Caenorhabditis elegans/genética , Regulación de la Expresión Génica , Secuencia de Aminoácidos , Animales , Bacillus/fisiología , Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/microbiología , Proteínas de Caenorhabditis elegans/química , Proteínas de Caenorhabditis elegans/metabolismo , Femenino , Glicosilación , Organismos Hermafroditas/citología , Organismos Hermafroditas/genética , Organismos Hermafroditas/metabolismo , Organismos Hermafroditas/fisiología , Locomoción , Masculino , Datos de Secuencia Molecular , Mutación , Fenotipo , Conducta Sexual Animal , Propiedades de SuperficieRESUMEN
Yersinia pestis forms a biofilm in the foregut of its flea vector that promotes transmission by flea bite. As in many bacteria, biofilm formation in Y. pestis is controlled by intracellular levels of the bacterial second messenger c-di-GMP. Two Y. pestis diguanylate cyclase (DGC) enzymes, encoded by hmsT and y3730, and one phosphodiesterase (PDE), encoded by hmsP, have been shown to control biofilm production in vitro via their opposing c-di-GMP synthesis and degradation activities, respectively. In this study, we provide further evidence that hmsT, hmsP, and y3730 are the only three genes involved in c-di-GMP metabolism in Y. pestis and evaluated the two DGCs for their comparative roles in biofilm formation in vitro and in the flea vector. As with HmsT, the DGC activity of Y3730 depended on a catalytic GGDEF domain, but the relative contribution of the two enzymes to the biofilm phenotype was influenced strongly by the environmental niche. Deletion of y3730 had a very minor effect on in vitro biofilm formation, but resulted in greatly reduced biofilm formation in the flea. In contrast, the predominant effect of hmsT was on in vitro biofilm formation. DGC activity was also required for the Hms-independent autoaggregation phenotype of Y. pestis, but was not required for virulence in a mouse model of bubonic plague. Our results confirm that only one PDE (HmsP) and two DGCs (HmsT and Y3730) control c-di-GMP levels in Y. pestis, indicate that hmsT and y3730 are regulated post-transcriptionally to differentially control biofilm formation in vitro and in the flea vector, and identify a second c-di-GMP-regulated phenotype in Y. pestis.
Asunto(s)
Proteínas Bacterianas/metabolismo , Biopelículas , GMP Cíclico/análogos & derivados , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Liasas de Fósforo-Oxígeno/química , Liasas de Fósforo-Oxígeno/metabolismo , Yersinia pestis/química , Animales , GMP Cíclico/química , Modelos Animales de Enfermedad , Ratones , Mutación , Fenotipo , Peste/metabolismo , Estructura Terciaria de Proteína , Siphonaptera , Virulencia/genéticaRESUMEN
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.
Asunto(s)
Variación Genética , Genoma Bacteriano/genética , Photorhabdus/genética , Xenorhabdus/genética , Animales , Cromosomas Bacterianos/genética , ADN Bacteriano/química , ADN Bacteriano/genética , Enterobacteriaceae/clasificación , Enterobacteriaceae/genética , Enterobacteriaceae/fisiología , Genómica/métodos , Interacciones Huésped-Parásitos , Interacciones Huésped-Patógeno , Insectos/microbiología , Insectos/parasitología , Datos de Secuencia Molecular , Nematodos/microbiología , Nematodos/fisiología , Photorhabdus/clasificación , Photorhabdus/fisiología , Filogenia , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADN , Especificidad de la Especie , Simbiosis , Xenorhabdus/clasificación , Xenorhabdus/fisiologíaRESUMEN
The cuticle of Caenorhabditis elegans, a complex, multi-layered extracellular matrix, is a major interface between the animal and its environment. Biofilms produced by the bacterial genus Yersinia attach to the cuticle of the worm, providing an assay for surface characteristics. A C. elegans gene required for biofilm attachment, bah-1, encodes a protein containing the domain of unknown function DUF23. The DUF23 domain is found in 61 predicted proteins in C. elegans, which can be divided into three distinct phylogenetic clades. bah-1 is expressed in seam cells, which are among the hypodermal cells that synthesize the cuticle, and is regulated by a TGF-beta signaling pathway.
Asunto(s)
Biopelículas , Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/química , Proteínas de Caenorhabditis elegans/genética , Cartilla de ADN , Técnica del Anticuerpo Fluorescente , Datos de Secuencia Molecular , Filogenia , Interferencia de ARN , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Transducción de Señal , Factor de Crecimiento Transformador beta/metabolismoRESUMEN
Bubonic plague is transmitted by fleas whose feeding is blocked by a Yersinia pestis biofilm in the digestive tract. Y. pestis also block feeding of Caenorhabditis elegans by forming a biofilm on the nematode head, making the nematode an experimentally tractable surrogate for fleas to study plague transmission. Arabinose 5-phosphate isomerase (API), encoded by Y. pestis yrbH, catalyses the conversion of ribulose 5-phosphate into arabinose 5-phosphate (A5P), the first committed step in the 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) biosynthesis pathway. Here we show that Y. pestis YrbH is a multifunctional protein required for both Kdo biosynthesis and biofilm formation on C. elegans. The YrbH protein contains four functional components: biofilm-related region 1 (B1), a sugar isomerase domain (SIS), biofilm-related region 2 (B2) and a cystathionine beta-synthase domain pair (CBS). B1, SIS and B2 are all required for API function, but any of the three is sufficient for a biofilm-related function. The CBS domain appears to negatively regulate the biofilm-related function.
Asunto(s)
Isomerasas Aldosa-Cetosa/fisiología , Proteínas Bacterianas/fisiología , Biopelículas/crecimiento & desarrollo , Caenorhabditis elegans/microbiología , Azúcares Ácidos/metabolismo , Yersinia pestis/fisiología , Secuencia de Aminoácidos , Animales , Caenorhabditis elegans/crecimiento & desarrollo , Eliminación de Gen , Modelos Animales , Datos de Secuencia Molecular , Peste/transmisión , Estructura Terciaria de Proteína , Yersinia pestis/genéticaRESUMEN
A wide variety of bacterial pathogens, as well as several fungi, kill C. elegans or produce non-lethal disease symptoms. This allows the nematode to be used as a simple, tractable model host for infectious disease. Human pathogens that affect C. elegans include gram-negative bacteria of genera Burkholderia, Pseudomonas, Salmonella, Serratia and Yersinia; gram-positive bacteria Enterococcus, Staphylococcus and Streptococcus; and the fungus Cryptococcus neoformans. Microbes that are not pathogenic to mammals, such as the insect pathogen Bacillus thuringiensis and the nematode-specific Microbacterium nematophilum, are also studied with C. elegans. Many of the pathogens investigated colonize the C. elegans intestine, and pathology is usually quantified as decreased lifespan of the nematode. A few microbes adhere to the nematode cuticle, while others produce toxins that kill C. elegans without a requirement for whole, live pathogen cells to contact the worm. The rapid growth and short generation time of C. elegans permit extensive screens for mutant pathogens with diminished killing, and some of the factors identified in these screens have been shown to play roles in mammalian infections. Genetic screens for toxin-resistant C. elegans mutants have identified host pathways exploited by bacterial toxins.
Asunto(s)
Caenorhabditis elegans/microbiología , Animales , Fenómenos Fisiológicos Bacterianos , Modelos Animales de Enfermedad , Hongos/fisiología , Humanos , Intestinos/microbiologíaRESUMEN
Lipopolysaccharide (LPS) is the major outer membrane component of gram-negative bacteria. The minimal LPS structure for viability of Escherichia coli and Salmonella enterica serovar Typhimurium is lipid A glycosylated with 3-deoxy-D-manno-octulosonic acid (Kdo) residues. Here we show that another member of the Enterobacteriaceae, Yersinia pestis, can survive without Kdo in its LPS.
Asunto(s)
Toxinas Bacterianas/metabolismo , Lípido A/metabolismo , Lipopolisacáridos/química , Yersinia pestis/metabolismo , Toxinas Bacterianas/química , Lípido A/análisis , Lipopolisacáridos/metabolismo , Relación Estructura-Actividad , Yersinia pestis/química , Yersinia pestis/fisiologíaRESUMEN
Yersinia pestis, the cause of bubonic plague, blocks feeding by its vector, the flea. Recent evidence indicates that blockage is mediated by an in vivo biofilm. Y. pestis and the closely related Yersinia pseudotuberculosis also make biofilms on the cuticle of the nematode Caenorhabditis elegans, which block this laboratory animal's feeding. Random screening of Y. pseudotuberculosis transposon insertion mutants with a C. elegans biofilm assay identified gmhA as a gene required for normal biofilms. gmhA encodes phosphoheptose isomerase, an enzyme required for synthesis of heptose, a conserved component of lipopolysaccharide and lipooligosaccharide. A Y. pestis gmhA mutant was constructed and was severely defective for C. elegans biofilm formation and for flea blockage but only moderately defective in an in vitro biofilm assay. These results validate use of the C. elegans biofilm system to identify genes and pathways involved in Y. pestis flea blockage.
Asunto(s)
Biopelículas , Caenorhabditis elegans/microbiología , Genes Bacterianos/genética , Siphonaptera/microbiología , Yersinia pestis/genética , Yersinia pestis/fisiología , Animales , Proteínas Bacterianas/genética , Proteínas Bacterianas/fisiología , Carbohidrato Epimerasas/genética , Carbohidrato Epimerasas/metabolismo , Mutación , Antígenos O/biosíntesis , Antígenos O/fisiología , Siphonaptera/fisiología , Yersinia pestis/enzimología , Yersinia pseudotuberculosis/genética , Yersinia pseudotuberculosis/fisiologíaRESUMEN
Bubonic plague is transmitted by fleas whose feeding is blocked by a mass of Yersinia pestis in the digestive tract. Y. pestis and the closely related Y. pseudotuberculosis also block the feeding of Caenorhabditis elegans by forming a biofilm on the nematode head. C. elegans mutants with severe motility defects acquire almost no biofilm, indicating that normal animals accumulate the biofilm matrix as they move through a Yersinia lawn. Using the lectin wheat germ agglutinin as a probe, we show that the matrix on C. elegans contains carbohydrate produced by Yersinia. The carbohydrate is present in bacterial lawns prior to addition of nematodes, indicating that biofilm formation does not involve signaling between the two organisms. Furthermore, biofilm accumulation depends on continuous C. elegans exposure to a lawn of Yersinia bacteria.
Asunto(s)
Biopelículas/crecimiento & desarrollo , Caenorhabditis elegans/microbiología , Movimiento , Yersinia pestis/crecimiento & desarrollo , Yersinia pseudotuberculosis/crecimiento & desarrollo , Animales , Caenorhabditis elegans/genética , Caenorhabditis elegans/fisiología , Lectinas/química , Lectinas/metabolismo , Aglutininas del Germen de Trigo/metabolismoRESUMEN
Bubonic plague is transmitted to mammals, including humans, by the bites of fleas whose digestive tracts are blocked by a mass of the bacterium Yersinia pestis. In these fleas, the plague-causing bacteria are surrounded by an extracellular matrix of unknown composition, and the blockage depends on a group of bacterial genes known as the hmsHFRS operon. Here we show that Y. pestis creates an hmsHFRS-dependent extracellular biofilm to inhibit feeding by the nematode Caenorhabditis elegans. Our results suggest that feeding obstruction in fleas is a biofilm-mediated process and that biofilms may be a bacterial defence against predation by invertebrates.
Asunto(s)
Biopelículas/crecimiento & desarrollo , Caenorhabditis elegans/microbiología , Caenorhabditis elegans/fisiología , Ingestión de Alimentos , Peste/microbiología , Yersinia pestis/fisiología , Animales , Caenorhabditis elegans/genética , Caenorhabditis elegans/crecimiento & desarrollo , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Genes Bacterianos/genética , Genes de Helminto/genética , Interacciones Huésped-Parásitos , Intestinos/microbiología , Mutación/genética , Yersinia pestis/genética , Yersinia pestis/crecimiento & desarrolloRESUMEN
During the establishment of a bacterial infection, the surface molecules of the host organism are of particular importance, since they mediate the first contact with the pathogen. In Caenorhabditis elegans, mutations in the srf-3 locus confer resistance to infection by Microbacterium nematophilum, and they also prevent biofilm formation by Yersinia pseudotuberculosis, a close relative of the bubonic plague agent Yersinia pestis. We cloned srf-3 and found that it encodes a multitransmembrane hydrophobic protein resembling nucleotide sugar transporters of the Golgi apparatus membrane. srf-3 is exclusively expressed in secretory cells, consistent with its proposed function in cuticle/surface modification. We demonstrate that SRF-3 can function as a nucleotide sugar transporter in heterologous in vitro and in vivo systems. UDP-galactose and UDP-N-acetylglucosamine are substrates for SRF-3. We propose that the inability of Yersinia biofilms and M. nematophilum to adhere to the nematode cuticle is due to an altered glycoconjugate surface composition of the srf-3 mutant.