Many marine sponges, hereafter termed high-microbial-abundance (HMA) sponges, harbor large and complex microbial consortia, including bacteria and archaea, within their mesohyl matrices. To investigate vertical microbial transmission as a strategy to maintain these complex associations, an extensive phylogenetic analysis was carried out with the 16S rRNA gene sequences of reproductive (n ‫؍‬ 136) and adult (n ‫؍‬ 88) material from five different Caribbean species, as well as all published 16S rRNA gene sequences from sponge offspring (n ‫؍‬ 116). The overall microbial diversity, including members of at least 13 bacterial phyla and one archaeal phylum, in sponge reproductive stages is high. In total, 28 vertical-transmission clusters, defined as clusters of phylotypes that are found both in adult sponges and their offspring, were identified. They are distributed among at least 10 bacterial phyla and one archaeal phylum, demonstrating that the complex adult microbial community is collectively transmitted through reproductive stages. Indications of host-species specificity and cospeciation were not observed. Mechanistic insights were provided using a combined electron microscopy and fluorescence in situ hybridization analysis, and an indirect mechanism of vertical transmission via nurse cells is proposed for the oviparous sponge Ectyoplasia ferox. Based on these phylogenetic and mechanistic results, we suggest the following symbiont transmission model: entire microbial consortia are vertically transmitted in sponges. While vertical transmission is clearly present, additional environmental transfer between adult individuals of the same and even different species might obscure possible signals of cospeciation. We propose that associations of HMA sponges with highly sponge-specific microbial communities are maintained by this combination of vertical and horizontal symbiont transmission.Sponges (phylum Porifera) are evolutionarily ancient Metazoa whose origin dates back about 600 million years to the Precambrian (26). With 7,000 formally described species and an estimated 15,000 extant species, sponges are among the most diverse marine invertebrate groups and are important components of all aquatic habitats, including freshwater environments, tropical reefs, and even the deep sea (19). Despite an enormous range of shapes, colors, and sizes, all sponges possess a relatively simple body plan which is adapted to a filter-feeding lifestyle (4). Large volumes of seawater are pumped through canals embedded in an extracellular matrix (55), termed the mesohyl, and microorganisms and small unicellular eukaryotes are taken up from the seawater with high efficiency, leaving the expelled water essentially sterile (37, 54).Numerous sponges live in permanent and close associations with microorganisms, and many of them host phylogenetically diverse populations of microbes (15,17,49). These microorganisms are located mainly extracellularly in the sponge mesohyl in high concentrations, contributing up to 40% of the sponge's biomass and...

Extraintestinal pathogenic and intestinal pathogenic (diarrheagenic) Escherichia coli differ phylogenetically and by virulence profiles. Classic theory teaches simple linear descent in this species, where non-pathogens acquire virulence traits and emerge as pathogens. However, diarrheagenic Shiga toxin-producing E. coli (STEC) O2:H6 not only possess and express virulence factors associated with diarrheagenic and uropathogenic E. coli but also cause diarrhea and urinary tract infections. These organisms are phylogenetically positioned between members of an intestinal pathogenic group (STEC) and extraintestinal pathogenic E. coli. STEC O2:H6 is, therefore, a ‘heteropathogen,’ and the first such hybrid virulent E. coli identified. The phylogeny of these E. coli and the repertoire of virulence traits they possess compel consideration of an alternate view of pathogen emergence, whereby one pathogroup of E. coli undergoes phased metamorphosis into another. By understanding the evolutionary mechanisms of bacterial pathogens, rational strategies for counteracting their detrimental effects on humans can be developed.Subject Categories Microbiology, Virology & Host Pathogen Interaction

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c Enterohemorrhagic Escherichia coli (EHEC), a subgroup of Shiga toxin (Stx)-producing E. coli (STEC), is a leading cause of diarrhea and hemolytic-uremic syndrome (HUS) in humans. However, urinary tract infections (UTIs) caused by this microorganism but not associated with diarrhea have occasionally been reported. We geno-and phenotypically characterized three EHEC isolates obtained from the urine of hospitalized patients suffering from UTIs. These isolates carried typical EHEC virulence markers and belonged to HUS-associated E. coli (HUSEC) clones, but they lacked virulence markers typical of uropathogenic E. coli. One isolate exhibited a localized adherence (LA)-like pattern on T24 urinary bladder epithelial cells. Since the glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) are well-known receptors for Stx but also for P fimbriae, a major virulence factor of extraintestinal pathogenic E. coli (ExPEC), the expression of Gb3Cer and Gb4Cer by T24 cells and in murine urinary bladder tissue was examined by thin-layer chromatography and mass spectrometry. We provide data indicating that Stxs released by the EHEC isolates bind to Gb3Cer and Gb4Cer isolated from T24 cells, which were susceptible to Stx. All three EHEC isolates expressed stx genes upon growth in urine. Two strains were able to cause UTI in a murine infection model and could not be outcompeted in urine in vitro by typical uropathogenic E. coli isolates. Our results indicate that despite the lack of ExPEC virulence markers, EHEC variants may exhibit in certain suitable hosts, e.g., in hospital patients, a uropathogenic potential. The contribution of EHEC virulence factors to uropathogenesis remains to be further investigated. Escherichia coli is one of the most versatile microorganisms that rapidly colonizes the gastrointestinal tract of newborns (1). Although E. coli usually represents an important commensal of the normal intestinal microbiota, other variants that are able to cause infections exist (1, 2). On the basis of their virulence properties and the site of infection, these bacteria are classified as intestinal pathogenic E. coli (IPEC), which are associated with diarrhea, and extraintestinal pathogenic E. coli (ExPEC), which cause infections beyond the intestinal tract (3). Enterohemorrhagic E. coli (EHEC) belongs to the IPEC group of bacteria and represents one of the main causative agents of diarrhea, hemorrhagic colitis (HC), and hemolytic-uremic syndrome (HUS) in humans (4). The characteristic main EHEC virulence markers include the locus of enterocyte effacement (LEE) pathogenicity island and Shiga toxin (Stx)-encoding bacteriophages. Additionally, other toxins, including the cytolethal distending toxin (CDT), EHEC hemolysin (Hly), serine protease EspP, subtilase cytotoxin, cyclomodulin Cif, and different siderophore systems, as well as adhesins can also contribute to EHEC pathogenesis (5). These EHEC virulence factors are absent from archetypal ExPEC strains.Similarly, the main ExPEC virulence fa...