Taxonomic composition and predicted functional potential of the sputum bacterial microbiome in Iraqi patients with bronchiectasis using 16S rRNA gene amplicon sequencing

Abstract

Bronchiectasis is a chronic respiratory disease characterized by persistent airway inflammation and recurrent infections. Although alterations in the airway microbiome have been reported, data from Middle Eastern populations remain limited. This study aimed to characterize the sputum bacterial microbiome and predict its functional potential in Iraqi patients with bronchiectasis using 16S rRNA gene (V3-V4) amplicon sequencing. Sputum samples were collected from 28 patients with non-cystic fibrosis bronchiectasis and 10 healthy individuals. Amplicon sequence variants (ASVs) were inferred using DADA2, taxonomic assignment was performed against the SILVA (v138.2) database, and alpha and beta diversity were assessed. Differential abundance was analysed using ALDEx2, and predicted functional profiles were inferred using Tax4Fun2 based on KEGG pathways. Taxonomic profiling identified 24 bacterial genera across seven phyla. Sputum microbiota was dominated by Pseudomonas, Streptococcus, Neisseria, and Haemophilus, with descriptive differences in the relative abundance of several genera between bronchiectasis and healthy controls. However, no significant differences were observed in alpha diversity, beta diversity, differential abundance after Benjamini-Hochberg correction, or predicted KEGG pathway abundances between groups in Iraqi patients with bronchiectasis using 16S rRNA gene amplicon sequencing. Although compositional trends were observed, no statistically significant differences in microbial diversity, differential abundance, or predicted functional pathways were detected. These findings provide a baseline for future larger, longitudinal studies investigating the airway microbiome in bronchiectasis.