Co-occurrence of Fe and in marine diazotroph Trichodesmium

The authors present a metaproteomic study of field-collected Trichodesmium colonies, focused on phosphate and iron stress 10 markers, and complement that study with a membrane crowding model, which I think is a nice approach to try and understand the observed co-limitation patterns for iron and phosphate. The study is comprehensive in that samples from multiple cruises and years are used; with all but one station (HOT) located in the Atlantic Ocean. Increasing the knowledge of nutrient limitation in natural Trichodesmium populations is certainly of interest, given that it seems to be connected to aggregation of Trichodesmium in some way, either directly or through a general C1 stress response. While the study as such 15 is valuable and should be published, I have a few major remarks that I think should be addressed before it is ready. a table, including the type of experiment (culture or field), absolute quantifications if stated, and fold-changes measured. I also suggest then being a little more careful in wording throughout the paper, and differentiating better how the results from different stations could be interpreted. Abstract. Trichodesmium is a globally important marine microbe that provides fixed nitrogen (N) to otherwise N limited ecosystems. In nature, nitrogen fixation is likely regulated by iron or phosphate availability, but the extent and interaction of these controls are unclear. From metaproteomics analyses using established protein biomarkers for iron and phosphate stress, we found that co-stress is the norm rather than the exception for field Trichodesmium colonies. Counter-intuitively, the nitrogenase enzyme was more abundant under co-stress than under single nutrient stress, consistent with the idea that Trichodesmium has a specific physiological state under nutrient co-stress, as opposed to single nutrient stress. Organic nitrogen uptake was observed to occur simultaneously with nitrogen fixation. Quantification of the phosphate ABC transporter PstA combined with a cellular model of nutrient uptake suggested that Trichodesmium is generally confronted by 130 the biophysical limits of membrane space and diffusion rates for iron and phosphate acquisition in the field. Colony formation may benefit nutrient acquisition from particulate and organic nutrient sources, alleviating these pressures. The results highlight that to predict the behavior of Trichodesmium , both Fe and P stress must be evaluated and understood simultaneously. Abstract. Trichodesmium is a globally Trichodesmium has a specific physiological state under as to nitrogen uptake was observed to occur simultaneously with nitrogen fixation. Quantification of the phosphate transporter PstA combined with a cellular model of nutrient uptake suggested that Trichodesmium is generally confronted by the biophysical limits of membrane space and diffusion rates for iron and phosphate acquisition in the field. Colony formation may benefit nutrient acquisition from particulate and organic nutrient sources, alleviating these pressures. The results highlight that to predict the behavior of Trichodesmium , both Fe and P stress must be evaluated and understood simultaneously. MS2 between and fmol μ using 10uL injections consistent with experimental injection volumes. Abstract. Trichodesmium is a globally important marine microbe that provides fixed nitrogen (N) to otherwise N limited ecosystems. In nature, nitrogen fixation is likely regulated by iron or phosphate availability, but the extent and interaction of 545 these controls are unclear. From metaproteomics analyses using established protein biomarkers for iron and phosphate stress, we found that co-stress is the norm rather than the exception for field Trichodesmium colonies. Counter-intuitively, the nitrogenase enzyme was more abundant under co-stress as opposed to single nutrient stress. This is consistent with the idea that Trichodesmium has a specific physiological state during nutrient co-stress. Organic nitrogen uptake was observed and occurred simultaneously with nitrogen fixation. Quantification of the phosphate ABC transporter PstA combined with a 550 cellular model of nutrient uptake suggested that Trichodesmium is generally confronted by the biophysical limits of membrane space and diffusion rates for iron and phosphate acquisition in the field. Colony formation may benefit nutrient acquisition from particulate and organic nutrient sources, alleviating these pressures. The results highlight that to predict the behavior of Trichodesmium , both Fe and P stress must be evaluated