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

Abstract The outer membrane protein W (OmpW) family comprises minor porins essential for environmental adaptation and host interactions in Gram-negative bacteria. However, ompW is conventionally treated as a ubiquitous single-copy gene, masking its true evolutionary complexity. Through comprehensive phylogenetic analysis across thousands of reference genomes, we reveal that ompW is present in nearly half of Gram-negative lineages, exhibiting a patchy distribution governed by a birth-and-death model of evolution with recurrent duplications and horizontal transfer. Notably, copy number expansions concentrate in lineages associated with eukaryotic hosts, linking paralog accumulation to niche adaptation. Experimental validation in Acinetobacter baumannii reveals four distinct loci that maintain high structural conservation despite sequence divergence, yet undergo profound functional specialization spanning from baseline physiological maintenance to modulating host colonization and persistence in vitro and in vivo . These findings dismantle the single-copy paradigm, demonstrating that widespread gene family expansion and paralog diversification drive the phenotypic plasticity required for bacteria to colonize hostile host environments.