Human and bacterial genomics and coevolution in diverse populations

The human body is home to more than ten thousand species of bacteria. Although bacterial colonisation is often considered synonymous with disease, the majority of colonising bacteria do not harm the host but are essential for human survival. This intricate human-bacterial relationship has developed through coevolution since humans’ earliest origins.

Despite being critical components of human health, exploration into the population genetics of bacteria has been largely neglected, especially for non-disease causing species. However, technological advancement means it is now financially viable to perform robust genomic investigation into such populations. This thesis investigates host-microbial correlations and coevolution with the host of three bacterial populations in geographically diverse healthy host populations. Two methods of coevolutionary study were employed, one based on geographic distribution of genetic variation in the oral commensal, Streptococcus mitis, and the other on the correlation between human genetic factors with either genetic variation in the opportunistic stomach pathogen, Helicobacter pylori, or the composition of the oral bacterial community.

Combined results of these studies concluded that whilst host genetics and the human-bacterial relationship did influence the evolution of bacterial species and communities, this could not explain all observed genetic variation. This thesis therefore concludes bacterial evolution is driven by a complex interaction of host genetics and environmental factors, elucidation of which requires further study.

Analysis of bacterial population genetics in healthy hosts across diverse populations is important not only in understanding the role of bacterial species and communities in human health and disease but will contribute to significant advancements in medical, anthropological and forensic disciplines in the future.