Genetic Contributions to Invasion and Biofilm Disruption in a Microbial Model Community

Abstract

This thesis investigates how a synthetic microbial community respond to environmental stress and microbial invasion, using the model community THOR—comprising Pseudomonas koreensis, Bacillus cereus, and Flavobacterium johnsoniae. Through microbiological assays, transposon mutagenesis (INSeq), and proteomics, the work links environmental conditions and genetic determinants to community stability and disruption. The aim was to explore how cooperative traits emerge and how pathogens like Pseudomonas aeruginosa interfere with these dynamics. Paper I shows that cooperative biofilm formation in THOR is highly temperature-sensitive, with peak synergy at 18 °C and collapse at higher temperatures, suggesting fragility in microbial interactions. Paper II demonstrates that P. aeruginosa invasion disrupts biofilm formation without altering species composition, indicating a mode of functional interference rather than direct competition. Paper III identifies chromosomal genes conferring resistance to ciprofloxacin and tetracycline, including mexH, rhlI, and cysA, though these did not influence community invasion. Paper IV reveals invasion-specific genes such as wzz, nqrD, and pvdE, essential for successful colonization of THOR biofilms. Paper V explores the role of pvdE in depth, showing that its overexpression enhances invasion and triggers broad regulatory changes beyond iron acquisition. This work highlights how microbial interactions depend on both environmental context and genetic regulation. Pathogens like P. aeruginosa can destabilize communities through subtle interference mechanisms, with specific genes enabling invasion. These findings advance our understanding of microbial ecology, virulence, and resilience, with implications for managing microbiomes in environmental and clinical settings.