PNNL

Abstract

To what extent genotypic differences translate to phenotypic variation remains a poorly understood issue of paramount importance for several cornerstone concepts of microbiology such as the species definition. Here, we take advantage of the completed genomic sequences, expressed proteomic profiles, and physiological studies of ten closely related Shewanella organisms to provide quantitative insights into this issue. Our analyses revealed that, despite the extensive horizontal gene transfer characterizing these genomes, the genotypic and phenotypic similarities among the organisms were generally predictable from their evolutionary relatedness. The power of the predictions depended, however, on the degree of ecological specialization of the organisms evaluated. Using the unprecedented genetic gradient formed by these genomes, we were able to isolate the effect of ecology from the effect of evolutionary divergence and rank the different cellular functions in terms of their rates of evolution. Our ranking also revealed that whole-cell protein expression differences among these organisms when grown under identical conditions were relatively larger than differences at the genome level, suggesting that similarity in gene regulation and expression should constitute another important parameter for (new) species description. Collectively, our results provide important new information towards beginning a system level understanding of bacterial species and genera.