Phylogenetic diversification of the PoxtA ribosomal protection determinant.

OBJECTIVES

Three ATP-binding cassette subfamily F (ABC-F) PoxtA protein sequences are currently represented in NCBI's Pathogen Detection Reference Gene Catalog (WP_002415638.1, WP_209691075.1, and WP_094899500.1), while the number of publicly available sequences has steadily increased. We therefore conducted a curated survey of PoxtA homologue diversity, distribution, amino acid variability, and dissemination-associated genetic contexts.

METHODS

WP accessions were retrieved using BLASTp nr and a corresponding data package was obtained from NCBI Datasets v18.0.1. Proteins were aligned with MAFFT v7.525, clustered with CD-HIT v4.8.1, and maximum likelihood trees inferred in IQ-TREE v2.4.0. Gene occurrence derived from GCF assemblies containing host or source metadata. Genetic contexts were then investigated through sequence alignments of genomic regions extracted from these datasets.

RESULTS

Among 83 non-redundant PoxtA-related WP accessions retrieved, 21 homologues clustered with canonical RefSeq PoxtA proteins, while the remaining proteins were more distantly related to ABC-F. Predominantly associated with Bacillota, homologues exhibited broad distribution across clinical, agricultural, food-associated, and environmental sources. Substitutions potentially affecting their ribosome interactions were identified mainly within the Arm subdomain and the antibiotic-resistance domain. Genomes encoding homologues exhibited diverse genetic contexts, including partial conservation of Tn6657, intact Tn6246 and Tn8026 structures, and atypical contexts carrying additional resistance genes.

CONCLUSIONS

Homologue diversification suggests ongoing adaptation and highlights an expanding repertoire of amino acid substitutions with yet unresolved structural and functional impacts. Genetic contexts likely underlie intra- and interspecies horizontal dissemination of homologue genes by promoting co-selection under antimicrobial selective pressures.