Bacterial wide genomic GC variation poses numerous interesting scientific questions, which center on the role evolution plays in shaping genome content and the mechanisms that abruptly alter such processes. In this study, eleven Kordiimonas genomes were obtained and processed for comparative genomic, phylogenetic, evolutionary, and statistical analyses. The phylogenomic reconstruction based on single-copy orthologous cluster protein sequences and overall genomic relatedness index calculations showed that the genus Kordiimonas could be separated into GC-rich (56.3 to 59.9%) and -poor (46.2 to 49.6%) groups, and Ca. Kordiimonas sp. UBA4487 should be reclassified to remove it from this genus. Comparisons of amino acid frequencies in the genus also indicated that the GC-rich and -poor groups had several significantly different amino acid usages. Evolutionary analysis revealed that the GC-poor group had significantly higher nonsynonymous and synonymous substitution rates than the GC-rich group did, and evolved from the GC-rich ancestor. Comparative genomics also demonstrated that the GC-rich group encoded more genes related to nitrogen metabolism and transport than the GC-poor group did, leading to ecological niche diversification of the two groups, which could reduce inter-species competition in similar environments. Our study characterized the evolutionary patterns involved in nucleotide substitutions and their trends, as well as metabolic changes at the genus level, which can shed light on the understanding of bacterial microevolution in the future.
Zhuo et al. (Tue,) studied this question.