Host-specific bacterial modulation of airway gene expression and alternative splicing.

The human microbiome varies extensively between individuals. While there are numerous studies investigating the effects of inter-individual differences on microbiome composition, there are few studies investigating inter-individual effects on microbial modulation of the host or host-specific effects. To address this knowledge gap, we colonized human bronchial epithelial air-liquid interface tissue cultures generated from six different adults with one of three phylogenetically diverse bacteria and compared how each microbe differentially modulated host gene expression in each of the six donors. Microbial treatment had the strongest effect on transcription, followed by donor-specific effects. Gene pathways differed markedly in their donor and microbe specificity; interferon expression was highly donor-dependent, while transcription of epithelial barrier and antibacterial innate immunity genes was predominantly microbially driven. Moreover, we evaluated whether microbial regulation of alternative splicing was modulated by the donor. Strikingly, we found significant nonredundant, donor-specific regulation of alternative splicing exclusively in the gram-positive commensal microbes. These findings highlight that microbial effects on the human airway epithelium are not only species-specific but also deeply individualized, underscoring the importance of the host context in shaping microbe-induced transcriptional and splicing responses.IMPORTANCEMicrobiota are integral regulators of host gene expression, utilizing diverse mechanisms that are shaped by the interplay between microbiome composition and inter-individual differences, i.e., host-specific factors. While previous studies have characterized inter-individual variation in microbiome composition and the effects of variable microbiome composition on the host, the extent to which host-specificity itself regulates host-microbe interactions remains poorly understood. In this study, we address this gap by characterizing changes in epithelial gene expression from six different human donors following colonization with one of three phylogenetically diverse bacteria. By systematically comparing donor-specific responses, we demonstrate that host specificity is a key determinant of the host transcriptional response to microbial colonization. Importantly, we demonstrate that the effects of host specificity are not uniform, but instead are dependent on the colonizing microbe. Our findings underscore the complexity of host-microbe relationships and establish host specificity as a significant factor shaping host-microbe interactions.