Aerobiosis is not associated with GC content and G to T mutations are not the signature of oxidative stress in prokaryotic evolution

Abstract

Oxidative stress is unavoidable for oxygen-consuming organisms. Guanine is the most fragile base with regard to oxidative stress and thus the most frequently damaged among the four bases. The incorporation of the damaged guanines into DNA strands and the replication of DNA containing damaged guanines causes G to T mutations at a frequency depending on the efficiency of DNA repair enzymes and the accuracy of replication enzymes. For this reason, aerobiosis is expected to decrease GC content. However, the opposite pattern of base composition in prokaryotes was reported 15 years ago. Although that study has been widely cited, its omission of the effect of shared ancestry requires a re-examination of the reliability of its results. In this study, using phylogenetically independent comparisons, we found that aerobic prokaryotes have significantly lower whole-genome GC contents than anaerobic ones.When the GC content was measured only at 4-fold degenerate sites, the difference between aerobic prokaryotes and anaerobic prokaryotes was greater, which is consistent with the possibility of a mutational force imposed by oxidative stress on the evolution of nucleotide composition.