{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T01:24:24Z","timestamp":1790040264685,"version":"4.0.1"},"reference-count":99,"publisher":"Oxford University Press (OUP)","issue":"1","license":[{"start":{"date-parts":[[2026,4,30]],"date-time":"2026-04-30T00:00:00Z","timestamp":1777507200000},"content-version":"vor","delay-in-days":119,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100002428","name":"Austrian Science Fund","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100002428","id-type":"DOI","asserted-by":"publisher"}]},{"name":"FWF Cluster of Excellence COE7"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2026,1,14]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Symbiotic associations between microorganisms often involve eukaryotes partnering with microbes for nutrient exchange, protection, and resource acquisition. Bacterial lineages like the Chlamydiota have evolved entirely symbiotic lifestyles, exploiting their eukaryotic hosts for energy, diverse metabolites, and shelter. The study of environmental chlamydiae\u2014outside the well-studied vertebrate host range\u2014has revealed diverging interactions on the mutualism\u2013parasitism spectrum. This highlights their potentially important roles in host\u2013microbe interactions underscoring the relevance of obtaining isolates from diverse environments and hosts. Here, we describe an isolate of a chlamydial symbiont of the freshwater cnidarian Hydra. The symbiont could be isolated and stably maintained in insect cell lines and represents a member of the recently described family-level lineage Chlamydiae Clade III for which we propose the name Endochlamydiaceae. Fluorescence and electron microscopy reveal the symbiont morphology and its endodermal location. Comparative genomics shows the isolate, named Endochlamydia hydrae, encodes a conserved set of genes involved in host invasion, communication, and pathogenicity. Instead of displaying unique genomic adaptations to its animal host, E. hydrae shows signs consistent with ongoing genome reorganisation and streamlining, suggesting a more recent host shift. Screening for closely related 16S rRNA gene sequences in public environmental microbiomes also indicates a broader host range. Moreover, exploration of environmental Hydra oligactis populations revealed they might serve as host for a wider spectrum of chlamydial species. This study highlights the evolutionary success of chlamydiae and their genomic toolkit to infect a wide range of hosts and their ecological significance by interacting with diverse organisms.<\/jats:p>","DOI":"10.1093\/ismejo\/wrag104","type":"journal-article","created":{"date-parts":[[2026,4,28]],"date-time":"2026-04-28T11:53:06Z","timestamp":1777377186000},"source":"Crossref","is-referenced-by-count":2,"title":["Stable association of a chlamydial symbiont with the freshwater predator\n                    <i>hydra<\/i>\n                    suggests broad host potential"],"prefix":"10.1093","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-8356-8244","authenticated-orcid":false,"given":"Angelika","family":"Schwarzhans","sequence":"first","affiliation":[{"name":"Centre for Microbiology and Environmental Systems Science, University of Vienna , Djerassiplatz 1, Vienna 1030, Vienna ,","place":["Austria"]},{"name":"Doctoral School in Microbiology and Environmental Science, University of Vienna , Djerassiplatz 1, Vienna 1030, Vienna ,","place":["Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0707-1202","authenticated-orcid":false,"given":"Justine","family":"Boutry","sequence":"additional","affiliation":[{"name":"CREEC\/CANECEV (CREES), MIVEGEC, Unit\u00e9 Mixte de Recherches, IRD 224\u2013CNRS 5290\u2013Universit\u00e9 de Montpellier , 911 avenue Agropolis, 34394 Montpellier Cedex 05, H\u00e9rault ,","place":["France"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6908-6493","authenticated-orcid":false,"given":"J\u00e1cint","family":"T\u00f6k\u00f6lyi","sequence":"additional","affiliation":[{"name":"MTA-DE \u201cMomentum\u201d Ecology, Evolution & Developmental Biology Research Group, Dept. of Evolutionary Zoology, University of Debrecen , Egyetem t\u00e9r 1, Debrecen 4032, Hajd\u00fa-Bihar County ,","place":["Hungary"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6874-862X","authenticated-orcid":false,"given":"Norbert","family":"Cyran","sequence":"additional","affiliation":[{"name":"Faculty of Life Sciences, Core Facility for Cell Imaging and Ultrastructure Research, University of Vienna , Djerassiplatz 1, 1030 Vienna, Vienna ,","place":["Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7528-4429","authenticated-orcid":false,"given":"Martin","family":"Kunert","sequence":"additional","affiliation":[{"name":"Centre for Microbiology and Environmental Systems Science, University of Vienna , Djerassiplatz 1, Vienna 1030, Vienna ,","place":["Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8309-5855","authenticated-orcid":false,"given":"Matthias","family":"Horn","sequence":"additional","affiliation":[{"name":"Centre for Microbiology and Environmental Systems Science, University of Vienna , Djerassiplatz 1, Vienna 1030, Vienna ,","place":["Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4100-832X","authenticated-orcid":false,"given":"Astrid","family":"Collingro","sequence":"additional","affiliation":[{"name":"Centre for Microbiology and Environmental Systems Science, University of Vienna , Djerassiplatz 1, Vienna 1030, Vienna ,","place":["Austria"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2026,4,30]]},"reference":[{"key":"2026060219240749100_ref1","doi-asserted-by":"publisher","first-page":"40","DOI":"10.1038\/s41564-022-01284-9","article-title":"Gene gain facilitated endosymbiotic evolution of Chlamydiae","volume":"8","author":"Dharamshi","year":"2023","journal-title":"Nat 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