Transcriptomic and physiological analyses of the dinoflagellate Karenia mikimotoi reveal non‐alkaline phosphatase‐based molecular machinery of ATP utilisation

Summary The ability to utilize dissolved organic phosphorus (DOP) is important for phytoplankton to survive the scarcity of dissolved inorganic phosphorus (DIP), and alkaline phosphatase (AP) has been the major research focus as a facilitating mechanism. Here we employed a unique molecular ecological approach and conducted a broader search for underpinning molecular mechanisms of adenosine triphosphate (ATP) utilization. Cultures of the dinoflagellate Karenia mikimotoi were set up in L1 medium (+P), DIP-depleted L1 medium (-P), and ATP-replacing-DIP medium (ATP). Differential gene expression was profiled for ATP and +P cultures using suppression subtractive hybridization (SSH) followed by 454 pyrosequencing, and RT-qPCR methods. We found that ATP supported a similar growth rate and cell yield as L1 medium and observed DIP release from ATP into the medium, suggesting that K. mikimotoi cells were expressing extracellular hydrolases to hydrolyze ATP. However, our SSH, qPCR and enzymatic activity assays indicated that 5'-nucleotidase (5NT), rather than AP, was responsible for ATP hydrolysis. Further gene expression analyses uncovered that intercellular purine metabolism was significantly changed following the utilization of ATP. Our findings reveal a multi-faceted machinery regulating ATP utilization and P metabolism in K. mikimotoi, and underscore AP activity is not the exclusive indicator of DOP utilization. This article is protected by copyright. All rights reserved.