Phytate as a phosphorus nutrient and anti-iron nutrient for phytoplankton: insights from diatom Phaeodactylum tricornutum

Jiashun Li¹, Kaidian Zhang¹, Xin Lin¹, Ling Li¹, Senjie Lin^1,2,3*

¹ State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, Fujian, China

² Laboratory of Marine Biology and Biotechnology, Qingdao National Laboratory of Marine Science and Technology, Qingdao 266000, Shandong, China

³ Department of Marine Sciences, University of Connecticut, Groton, CT 06340, USA

*Correspondence: senjie.lin@uconn.edu

Phytoplankton have evolved a capability to acquire phosphorus (P)-nutrient from dissolved organic phosphorus (DOP) since the preferred form, dissolved inorganic phosphate (Pi), is often limited in parts of the ocean. Phytic acid (PA) is abundantly synthesized in plants and rich in excreta of animals, potentially enriching the DOP pool in coastal oceans. However, whether and how PA may be used by phytoplankton are poorly understood. Here, we investigated PA utilization and underlying metabolic pathways in the diatom model Phaeodactylum tricornutum. With PA as the sole P source, P. tricornutum growth rate and cell yield were significantly higher than that under the P-deprived condition but markedly lower than that under the Pi-replete condition. The replacement of phytate for DIP caused changes in multiple metabolic pathways, indicative of direct participation of PA in the phytoplankter’s metabolic pathways. Strikingly, PA-grown P. tricornutum exhibited iron-stress physiological and transcriptomic signals. These results suggest that PA is bioavailable to P. tricornutum but may chelate iron rendering it unavailable, revealing potential two-faceted impacts of a DOP on phytoplankton nutrition.

Keywords: Phaeodactylum tricornutum; phosphorus utilization mechanism; dissolved organic phosphorus; nutrient utilization; phytic acid