Cross-species evolutionary rewiring in the enteric bacterium Campylobacter

The lateral transfer of genes among bacterial strains and species has
opposing effects, conferring potentially beneficial adaptations whilst
introducing disharmony in coadapted genomes. The prevailing outcome will depend
upon the fitness cost of disrupting established epistatic interactions between
genes. It is challenging to understand this in nature because it
requires population-scale analysis of recombination and genomic coadaptation,
and laboratory confirmation of the functional significance of genotype
variation. By assigning the ancestry of DNA in the genomes of two
species of the world’s most common enteric bacterial pathogen, we show that up
to 28% of the <i>Campylobacter coli</i>
genome has been recently introgressed from <i>Campylobacter jejuni. </i>Then,
by quantifying covariation across the genome we show that &gt;83% of putative
epistatic links are between introgressed <i>C. jejuni </i>genes in divergent (&gt;20kb
apart) genomic positions, consistent with independent acquisition. Much of this
covariation is between 16 genes, with
just 5 genes accounting for 99% of SNP pairs, and laboratory mutagenesis and
complementation cloning assays demonstrated functional links between these genes, specifically related to formate
dehydrogenase (FDH) activity. These findings suggest that the genetic
confederations that define genomic species may be transient. Even for complex
traits such as central metabolism in the bacterial cell, conditions can arise
where epistatic genes can be decoupled, transferred and reinstated in a new
genetic background.