The cyanobacteria Prochlorococcus is a cyanbacterial genus, with some strains adapted to sea surface environments, which are poor in nutrients and have high-light intensity, and some strains adapted to deep sea conditions, which have relatively higher concentrations of nitrogen and phosphorus and lower light intensity. Here, we report pairwise comparisons between strains isolated from different depths of the same sea, which reveal a close association between atomic composition of the proteome and the availability nitrogen and phosphorus in the environment. The atomic composition of proteomes differs significantly among Prochlorococcus strains with different supplies of nitrogen in vivo; these different Supplies result from different capacities for nitrogen assimilation. We repeated Our whole-proteome analysis with the core proteomes of Prochlorococcus and obtained similar results. Our findings indicate that the elemental composition of proteomes is shaped by the availability of resources in the environment. (c) 2008 Elsevier Inc. All rights reserved.