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Protein markers of cyanobacterial stress
Nutrients including iron, nitrogen, and phosphorus limit primary productivity in the oceans. Determining how abundant cyanobacteria such as Prochlorococcus adapt to nutrient stress across marine settings requires accurate molecular assays. Saito et al. developed a proteomic and metaproteomic approach capable of targeting specific metabolic biomarkers from mixed communities in seawater (see the Perspective by Moore). Prochlorococcus proteins are indicative of a major limiting nutrient across a wide transect in the Pacific Ocean; however, they also show that the limitation of multiple nutrients at overlapping biomes is an additional source of stress.
Abstract
Marine primary productivity is strongly influenced by the scarcity of required nutrients, yet our understanding of these nutrient limitations is informed by experimental observations with sparse geographical coverage and methodological limitations. We developed a quantitative proteomic method to directly assess nutrient stress in high-light ecotypes of the abundant cyanobacterium Prochlorococcus across a meridional transect in the central Pacific Ocean. Multiple peptide biomarkers detected widespread and overlapping regions of nutritional stress for nitrogen and phosphorus in the North Pacific Subtropical Gyre and iron in the equatorial Pacific. Quantitative protein analyses demonstrated simultaneous stress for these nutrients at biome interfaces. This application of proteomic biomarkers to diagnose ocean metabolism demonstrated Prochlorococcus actively and simultaneously deploying multiple biochemical strategies for low-nutrient conditions in the oceans.
