  We perform an exhaustive analysis of genome statistics for organisms,
particularly extremophiles, growing in a wide range of physicochemical
conditions. Specifically, we demonstrate how the correlation between the
frequency of amino acids and their molecular weight, preserved on average,
typically decreases as optimal growth temperature increases. We show how the
relation between codon degeneracy and amino acid mass is enforced across these
organisms. We assess the occurrence of contiguous amino acids, finding several
significant short words, often containing cysteine, histidine or proline.
Typically, the significance of these words is independent of growth
temperature. In a novel approach, first-passage distributions are used to
capture correlations between discontiguous residues. We find a nearly universal
exponential background that we relate to properties of the aforementioned
individual amino acid frequencies. We find this approach reliably extracts
correlations that depend on growth temperature, some of which have not been
previously characterized.

Genomics;Populations and Evolution;Quantitative Methods