000K utf8 1100 $c2022 1500 eng 2050 urn:nbn:de:gbv:8:3-2022-00559-6 2051 10.3389/fmicb.2022.869666 3000 Bathia, Jay Rajesh 3010 Bosch, Thomas 3010 Fraune, Sebastian 3010 Lachnit, Tim 3010 Rosenstiel, Philip 3010 Schröder, Katja 4000 Symbiotic Algae of Hydra viridissima Play a Key Role in Maintaining Homeostatic Bacterial Colonization [Bathia, Jay Rajesh] 4209 The freshwater polyp Hydra viridissima (H. viridissima) harbors endosymbiotic Chlorella algae in addition to a species-specific microbiome. The molecular basis of the symbiosis between Hydra and Chlorella has been characterized to be metabolic in nature. Here, we studied the interaction between the extracellularly located microbiota and the algal photobiont, which resides in Hydra's endodermal epithelium, with main focus on Legionella bacterium. We aimed at evaluating the influence of the symbiotic algae on microbial colonization and in shaping the host microbiome. We report that the microbiome composition of symbiotic and aposymbiotic (algae free) H. viridissima is significantly different and dominated by Legionella spp. Hvir in aposymbiotic animals. Co-cultivation of these animals resulted in horizontal transmission of Legionella spp. Hvir bacteria from aposymbiotic to symbiotic animals. Acquisition of this bacterium increased the release of algae into ambient water. From there, algae could subsequently be taken up again by the aposymbiotic animals. The presence of algal symbionts had negative impact on Legionella spp. Hvir and resulted in a decrease of the relative abundance of this bacterium. Prolonged co-cultivation ultimately resulted in the disappearance of the Legionella spp. Hvir bacterium from the Hydra tissue. Our observations suggest an important role of the photobiont in controlling an invasive species in a metacommunity and, thereby, shaping the microbiome. 4950 https://doi.org/10.3389/fmicb.2022.869666$xR$3Volltext$534 4950 https://nbn-resolving.org/urn:nbn:de:gbv:8:3-2022-00559-6$xR$3Volltext$534 4961 https://macau.uni-kiel.de/receive/macau_mods_00002976 5051 610 5550 Co-cultivation 5550 horizontal transmission 5550 Microbiome 5550 Symbiosis 5550 Tripartite Interactions