Mucoid Pseudomonas aeruginosa-derived alginate modulates innate immune transcriptional responses and promotes intracellular growth of Mycobacterium tuberculosis and non-tuberculous mycobacteria.

Pulmonary dysbiosis has been increasingly associated with tuberculosis susceptibility, relapse, and treatment failure; however, the mechanistic contribution of specific airway pathogens remains poorly understood. Pseudomonas aeruginosa, particularly its mucoid phenotype characterized by alginate overproduction, is frequently detected in chronic lung diseases and tuberculosis-associated microbiomes. Here, we investigated whether mucoid P. aeruginosa and alginate modulate innate immune responses during Mycobacterium tuberculosis and non-tuberculous mycobacteria infection. Using human type II pneumocytes and monocyte-derived macrophages, we showed that heat-killed mucoid P. aeruginosa significantly enhances intracellular growth of M. tuberculosis and Mycobacterium abscessus, compared with the non-mucoid phenotype. Exogenous alginate reproduced these effects in a dose- and time-dependent manner without directly promoting mycobacterial growth. Alginate was associated with reduced mRNA expression of antimicrobial peptides (LL-37, hBD-2, hBD-3) and key pro- and anti-inflammatory cytokines in Mtb-infected macrophages, while inducing a delayed inflammatory transcriptional response in pneumocytes that was insufficient to control intracellular mycobacterial growth. These findings identify alginate as an immunomodulatory factor capable of modulating innate immune transcriptional responses and promoting mycobacterial persistence, providing mechanistic insight into how mucoid P. aeruginosa may contribute to tuberculosis progression in dysbiotic lungs.