RT Journal Article SR Electronic T1 Metabolic co-dependence drives the evolutionary ancient Hydra-Chlorella symbiosis JF bioRxiv FD Cold Spring Harbor Laboratory SP 234757 DO 10.1101/234757 A1 Hamada, Mayuko A1 Schröder, Katja A1 Bathia, Jay A1 Kürn, Ulrich A1 Fraune, Sebastian A1 Khalturina, Mariia A1 Khalturin, Konstantin A1 Shinzato, Chuya A1 Satoh, Nori A1 Bosch, Thomas C.G. YR 2018 UL http://biorxiv.org/content/early/2018/01/15/234757.abstract AB Many multicellular organisms rely on symbiotic associations for support of metabolic activity, protection, or energy. Understanding the mechanisms involved in controlling such interactions remains a major challenge. In an unbiased approach we identified key players that control the symbiosis between Hydra viridissima and its photobiont Chlorella sp. A99. We discovered significant upregulation of Hydra genes encoding a phosphate transporter and glutamine synthetase suggesting regulated nutrition supply between host and symbionts. Interestingly, supplementing the medium with glutamine temporarily supports in vitro growth of the otherwise obligate symbiotic Chlorella, indicating loss of autonomy and dependence on the host. Genome sequencing of Chlorella A99 revealed a large number of amino acid transporters and a degenerated nitrate assimilation pathway, presumably as consequence of the adaptation to the host environment. Our observations portray ancient symbiotic interactions as a codependent partnership in which exchange of nutrients appears to be the primary driving force.