# Whole-tissue imaging reveals intrastrain diversity shapes the spatial organization of Pseudomonas aeruginosa in a murine infection model

## TL;DR

The study shows how genetic diversity within Pseudomonas aeruginosa affects its spatial organization in lung infections.

## Contribution

Demonstrates that intrastrain OSA diversity alters microbiogeography in a murine infection model.

## Key findings

- OSA-deficient variants increase population size and alter spatial organization in synthetic sputum.
- OSA-deficient cells lead to larger wild-type aggregates in murine airways.
- Intrastrain genetic heterogeneity reshapes infection microbiogeography at the micron scale.

## Abstract

Intrastrain genetic and phenotypic heterogeneity of Pseudomonas aeruginosa is a hallmark of chronic lung infections in individuals with cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Although the coexistence of multiple P. aeruginosa lineages within a single host is well documented, the impact of this heterogeneity on infection microbiogeography remains poorly understood. We previously showed that loss of the lipopolysaccharide (LPS) O-specific antigen (OSA) alters P. aeruginosa aggregate assembly. Since OSA-deficient variants are common in chronic pulmonary infections and associated with increased pathogenesis and immune evasion, we investigated whether intrastrain OSA diversity shapes infection microbiogeography. We constructed mixed populations containing equal ratios of OSA-deficient variants and wild-type (WT) cells and examined aggregate assembly and population structures in a synthetic CF sputum model (SCFM2). To assess OSA heterogeneity in vivo, we used a murine pneumonia model combined with hybridization chain reaction (HCR) RNA-FISH and whole-tissue clearing to visualize spatial organization in the airways. In SCFM2, OSA-deficient variants increased total population size, reduced WT aggregate size, and altered spatial organization. We employed 2-plex HCR RNA-FISH to distinguish WT and OSA-deficient variants in murine lungs. Interestingly, in contrast to in vitro conditions, OSA-deficient cells led to significantly larger WT aggregates in the airways. These findings highlight the role of intrastrain genetic heterogeneity in shaping infection microbiogeography and provide a framework for understanding how population dynamics influence microbial physiology and host-pathogen interactions at the micron scale.

Intrastrain genetic and phenotypic diversity within Pseudomonas aeruginosa populations is common in chronic pulmonary infections. While this intrastrain heterogeneity is a hallmark of chronic infection, its consequences for the spatial organization of P. aeruginosa within the airways remain unclear. Here, we demonstrate that the loss of O-specific antigen in a subpopulation of P. aeruginosa significantly alters the spatial architecture of P. aeruginosa, without changing the total population size or composition. Using a combination of tissue clearing and hybridization chain reaction RNA-FISH in a murine lung infection model, we mapped the localization of genetically distinct P. aeruginosa variants in mixed populations in vivo. These findings reveal that genetic diversification within a strain can reshape the infection landscape at the micron scale, highlighting the overlooked role of intrastrain dynamics in shaping the microbiogeography of infections and influencing host-pathogen interactions.