Expression of a xanthine permease and phosphate transporter in cultures and field populations of the harmful alga Aureococcus anophagefferens: tracking nutritional deficiency during brown tides

Targeted gene expression using quantitative reverse transcription polymerase chain reaction (qRT‐PCR) was employed to track patterns in the expression of genes indicative of nitrogen or phosphorus deficiency in the brown tide‐forming alga Aureococcus anophagefferens. During culture experiments, a xanthine/uracil/vitamin C permease (XUV) was upregulated ∼20‐fold under nitrogen‐deficient conditions relative to a nitrogen‐replete control and rapidly returned to nitrogen‐replete levels after nitrogen‐deficient cells were resupplied with nitrate or ammonium. It was not responsive to phosphorus deficiency. Expression of an inorganic phosphate transporter (PTA3) was enriched ∼10‐fold under phosphorus‐deficient conditions relative to a phosphorus‐replete control, and this signal was rapidly lost upon phosphate resupply. PTA3 was not upregulated by nitrogen deficiency. Natural A. anophagefferens populations from a dense brown tide that occurred in Long Island, NY, in 2009 were assayed for XUV and PTA3 expression and compared with nutrient concentrations over the peak of a bloom. Patterns in XUV expression were consistent with nitrogen‐replete growth, never reaching the values observed in N‐deficient cultures. PTA3 expression was highest prior to peak bloom stages, reaching expression levels within the range of P‐deficient cultures. These data highlight the value of molecular‐level assessments of nutrient deficiency and suggest that phosphorus deficiency could play a role in the dynamics of destructive A. anophagefferens blooms.