TY - JOUR T1 - Metabolic co-dependence drives the evolutionary ancient <em>Hydra-Chlorella</em> symbiosis JF - bioRxiv DO - 10.1101/234757 SP - 234757 AU - Mayuko Hamada AU - Katja Schröder AU - Jay Bathia AU - Ulrich Kürn AU - Sebastian Fraune AU - Mariia Khalturina AU - Konstantin Khalturin AU - Chuya Shinzato AU - Nori Satoh AU - Thomas C.G. Bosch Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/01/15/234757.abstract N2 - 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. ER -