| Description |
Escherichia coli is a Gram-negative bacterial species with both great biological diversity and important clinical relevance. To study its population structure in both world-wide and genome-wide scales, we scrutinise phylogenetically 104 high-quality complete genomes of diverse human/animal hosts, among which 45 are new additions to the collection; most of them are clustered into two major clades: Vig (vigorous) and Slu (sluggish). The two clades not only show distinct physiological features but also genome content and sequence variation. Limited recombination and horizontal gene transfer separate the two clades, as opposed to extensive intra-clade gene flow that functionally homogenizes even commensal and pathogenic strains. The two clades that are genetically isolated should be recognized as two subspecies both independently represent a continuum of possibilities range from commensal to pathogenic phenotype. Additionally, the frequent intra-clade recombinant events, often in larger fragments of over 5kb, indicates possibility of highly-efficient gene transfer mechanism depending on inheritance. Underlying molecular mechanisms that constitute such recombinant barrier between the subspecies deserve further exploration and investigations among broader microbial taxa. |
