Comparative and phylogenomic analysis of Chlamydia pneumoniae reveals unique carbohydrate active enzyme family (GT5) among respiratory isolates.

Chlamydia pneumoniae is an obligatory intracellular pathogen found in humans and animals. Understanding the genomic diversity is crucial for unravelling its pathogenic mechanisms and transmission dynamics. In this study, 14 complete genomes of C. pneumoniae strains were compared for functional diversity analysis. The koala isolate LPCoLN appears as a phylogenetically distinct, showing the fewest accessory genes and the highest incorporation of unique or absent genes among the strains analyzed. Functional annotation indicates that certain metabolic pathways between the LPCoLN and the human respiratory strain AR39 were the same, which is most likely due to phage-associated elements present in AR39. The presence of the GT5 CAZyme family is significantly associated with strains of respiratory origin, suggesting a potential role in respiratory adaptation and pathogenic strategies, including tissue colonization, immune evasion, and niche-specific persistence. The strong association between GT5 CAZymes and respiratory-origin strains highlights their potential as diagnostic markers and therapeutic targets.