Acclimation of <scp><i>E</i></scp><i>miliania huxleyi</i> (1516) to nutrient limitation involves precise modification of the proteome to scavenge alternative sources of <scp>N</scp> and <scp>P</scp>

<jats:title>Summary</jats:title><jats:p>Limitation of marine primary production by the availability of nitrogen or phosphorus is common. <jats:styled-content style="fixed-case"><jats:italic>E</jats:italic></jats:styled-content><jats:italic>miliania huxleyi</jats:italic>, a ubiquitous phytoplankter that plays key roles in primary production, calcium carbonate precipitation and production of dimethyl sulfide, often blooms in mid‐latitude at the beginning of summer when inorganic nutrient concentrations are low. To understand physiological mechanisms that allow such blooms, we examined how the proteome of <jats:styled-content style="fixed-case"><jats:italic>E</jats:italic></jats:styled-content><jats:italic>. huxleyi</jats:italic> (strain 1516) responds to <jats:styled-content style="fixed-case">N</jats:styled-content> and <jats:styled-content style="fixed-case">P</jats:styled-content> limitation. We observed modest changes in much of the proteome despite large physiological changes (e.g. cellular biomass, <jats:styled-content style="fixed-case">C</jats:styled-content>, <jats:styled-content style="fixed-case">N</jats:styled-content> and <jats:styled-content style="fixed-case">P</jats:styled-content>) associated with nutrient limitation of growth rate. Acclimation to nutrient limitation did however involve significant increases in the abundance of transporters for ammonium and nitrate under <jats:styled-content style="fixed-case">N</jats:styled-content> limitation and for phosphate under <jats:styled-content style="fixed-case">P</jats:styled-content> limitation. More notable were large increases in proteins involved in the acquisition of organic forms of <jats:styled-content style="fixed-case">N</jats:styled-content> and <jats:styled-content style="fixed-case">P</jats:styled-content>, including urea and amino acid/polyamine transporters and numerous <jats:styled-content style="fixed-case">C</jats:styled-content>‐<jats:styled-content style="fixed-case">N</jats:styled-content> hydrolases under <jats:styled-content style="fixed-case">N</jats:styled-content> limitation and a large upregulation of alkaline phosphatase under <jats:styled-content style="fixed-case">P</jats:styled-content> limitation. This highly targeted reorganization of the proteome towards scavenging organic forms of macronutrients gives unique insight into the molecular mechanisms that underpin how <jats:styled-content style="fixed-case"><jats:italic>E</jats:italic></jats:styled-content><jats:italic>. huxleyi</jats:italic> has found its niche to bloom in surface waters depleted of inorganic nutrients.</jats:p>