Phosphate release due to excess alkaline phosphatase activity in <i>Trichodesmium erythraeum</i>

Abstract

Abstract:We investigated the dependence of alkaline phosphatase activity (APA) on temperature and light intensity in cultured strains of the diazotroph Trichodesmium erythraeum isolated from the Kuroshio Current in the East China Sea. In contrast to the low levels of APA observed under phosphorus (P)-replete conditions, cultures grown under Plimited conditions exhibited strong APA, and the levels steadily increased with increases in temperature and irradiance from 22-30°C and 40-260 µmol m, respectively. Based on the chlorophyll a and APA levels in actively growing T. erythraeum, the mean hydrolyzing time required to double the cellular P quota was estimated to be 0.68 and 9.7 times shorter than the reported values under P-replete and P-limited conditions, respectively. This strongly suggests that APA under P-limited conditions is excessively active compared with the cellular P requirement. Furthermore, under P limitation intense bacterial aggregations were observed with fluorescence microscopy around the T. erythraeum trichomes in the same location as the visualized APA, suggesting enhancement of bacterial growth by surplus phosphate due to the excess APA, as well as possible release of dissolved organic matter from T. erythraeum. The present study suggests an important role for T. erythraeum as a phosphate supplier to other organisms in the oligotrophic ocean.

Co-occurrence of Fe and P stress in natural populations of the marine diazotroph &lt;i&gt;Trichodesmium&lt;/i&gt;

“…Siderophore production is energetically and nutritionally expensive, so it is most advantageous when resource concentrations are high and loss is low, as would occur in the center of a colony (Leventhal et al, 2019). Colonies may similarly enjoy advantages for phosphate acquisition, particularly when the excreted enzyme alkaline phosphatase is utilized to access organic sources (Frischkorn et al, 2018;Orchard, 2010;Orcutt et al, 2013;Yamaguchi et al, 2016;Yentsch et al, 1970). Additionally, the concentration of cells in a colony means that the products of nitrogen fixation, including urea, can be recycled and are less likely to be lost to the environment.…”

Co-occurrence of Fe and P stress in natural populations of the marine diazotroph &lt;i&gt;Trichodesmium&lt;/i&gt;

“…Siderophore production is energetically and nutritionally expensive, so it is most advantageous when resource concentrations are high and loss is low, as would occur in the center of a colony (Leventhal et 355 al., 2019). Colonies may similarly enjoy advantages for phosphate acquisition, particularly when the excreted enzyme alkaline phosphatase is utilized to access organic sources (Frischkorn et al, 2018;Elizabeth Duncan Orchard, 2010;Orcutt et al, 2013;Yamaguchi et al, 2016;Yentsch et al, 1970). Additionally, the concentration of cells in a colony means that the products of nitrogen fixation, including urea, can be recycled and are less likely to be lost to the environment.…”