Fig 1.
Conceptual overview of HGT inference methods.
(1) Parametric methods infer HGT by computing a statistic, here GC content, for a sliding window and comparing it to the typical range over the entire genome, here indicated between the two red horizontal lines. Regions with atypical values are inferred as having been horizontally transferred. (2) Phylogenetic approaches rely on the differences between genes and species tree evolution that result from HGT. Explicit phylogenetic methods reconstruct gene trees and infer the HGT events likely to have resulted into that particular gene tree. Implicit phylogenetic methods bypass gene tree reconstruction, e.g., by looking at discrepancies between pairwise distances between genes and their corresponding species.
Fig 2.
Average GC content of coding regions compared to the genome size for selected bacteria.
There is considerable variation in average GC content across species, which makes it relevant as a genomic signature.