Abstract
Phosphorus (P) limits primary production in regions of the surface ocean, and many plankton species exhibit specific physiological responses to P deficiency. The metabolic response of Micromonas pusilla, an ecologically relevant marine photoautotroph, to P deficiency was investigated using metabolomics and comparative genomics. The concentrations of some intracellular metabolites were elevated in the P-deficient cells (e.g. xanthine, inosine), and genes involved in the associated metabolic pathways shared a predicted conserved amino acid motif in the non-coding regions of each gene. The presence of the conserved motif suggests that these genes may be co-regulated, and the motif may constitute a regulatory element for binding a transcription factor, specifically that of Psr1 (phosphate starvation response). A putative phosphate starvation response gene (psr1-like) was identified in M. pusilla with homology to well characterized psr1/phr1 genes in algae and plants, respectively. This gene appears to be present and expressed in other marine algal taxa (e.g. Emiliania huxleyi) in field sites that are chronically P limited. Results from the present study have implications for understanding phytoplankton taxon-specific roles in mediating P cycling in the ocean.
Highlights
Phosphorus (P) is a critical element for life, and is found in lipid membranes, genetic material, and energy storage compounds
Our combined metabolomics and comparative genomic analyses of the response of Micromonas pusilla CCMP1545 to P deficiency has led to 3 conclusions: (1) there was an observable shift in intracellular metabolite composition, (2) a psr1-like gene is expressed in M. pusilla and other marine phytoplankton, and (3) the genes regulated by the Psr1like protein may differ amongst algal species
M. pusilla exhibits a metabolic shift in response to P deficiency. Some metabolites such as guanosine, pantothenate, 2, 3-dihydroxybenzoate, and leucine, and inosine were lower in concentration on average in the extracellular P-deficient treatment, but there were no significant differences between treatments
Summary
Phosphorus (P) is a critical element for life, and is found in lipid membranes, genetic material, and energy storage compounds. While the experimental designs differ slightly across studies, the aggregate results indicate the presence of both taxon-specific differences and crosstaxon similarities in the physiological response of phytoplankton to P deficiency (Rengefors et al 2003, Lomas et al 2004, Lin et al 2016, Martiny et al 2020) These strategies all minimize non-critical P utilization and maximize P uptake, and play important roles in structuring phytoplankton assemblages in the oceans (Dyhrman & Ruttenberg 2006, Dyhrman et al 2009, Martin et al 2011, Rokitta et al 2016, Guo et al 2018)
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