9Ocean microbes are responsible for about 50% of primary production on Earth, and are strongly 10 affected by environmental resource availability. However, selective forces resulting from 11 environmental conditions are not well understood. We studied selection by examining single-12 nucleotide variants in the marine environment, and discovered strong purifying selective forces 13 exerted across marine microbial genes. We present evidence indicating that this selection is 14 driven by the environment, and especially by nitrogen availability. We further corroborate that 15 nutrient availability drives this 'resource-driven' selection by showing stronger selection on highly 16 expressed and extracellular genes, that are more resource-consuming. Finally, we show that the 17 standard genetic code, along with amino acid abundances, facilitates nutrient conservation by 18 providing robustness to mutations that increase nitrogen and carbon consumption. Notably, this 19 robustness generalizes to multiple taxa across all domains of life, including the Human genome, 20 and manifests in the code structure itself. Overall, we uncover overwhelmingly strong purifying 21 selective pressure across marine microbial life that may have contributed to the structure of our 22 genetic code. 23 could be attributed to the different rates of synonymous mutations between the high-and low-595 nitrate groups, which, combined with simplex properties, may affect observed nonsynonymous