Evolutionary expansion of the bacterial ompW gene family enables functional diversification during host adaptation

The outer membrane protein W (OmpW) family consists of minor porins that are crucial for environmental adaptation and host interactions in Gram-negative bacteria. However, the ompW gene is often considered a ubiquitous single-copy gene, which conceals its significant evolutionary complexity. Recent phylogenetic analysis of thousands of reference genomes has revealed that ompW is present in nearly half of all Gram-negative lineages.

The distribution of ompW appears to be patchy, governed by a birth-and-death model of evolution characterized by recurrent duplications and horizontal gene transfer.

Interestingly, the copy number expansions of ompW tend to concentrate in lineages that have developed associations with eukaryotic hosts. This discovery suggests a potential link between paralog accumulation and niche adaptation. In experimental studies using Acinetobacter baumannii, four distinct loci were identified that maintain high structural conservation despite considerable sequence divergence.

Despite these variations, these loci have undergone substantial functional specialization, ranging from baseline physiological maintenance to the modulation of host colonization and persistence both in vitro and in vivo.

These findings challenge the long-held belief that ompW is a single-copy gene. Instead, they demonstrate that extensive gene family expansion and paralog diversification are key drivers of the phenotypic plasticity necessary for bacteria to successfully colonize hostile host environments.