Biomineralization strongly modulates the formation of Proteus mirabilis and Pseudomonas aeruginosa dual-species biofilms

Proteus mirabilis and Pseudomonas aeruginosa are common pathogens that often form biofilms together in catheter-associated urinary tract infections (CAUTI). However, the interactions between these two species in biofilms are largely unknown. Proteus mirabilis induces ureolytic biomineralization that substantially modifies key biofilm properties including morphology, persistence and recalcitrance to antimicrobial therapy. These processes are well known to complicate CAUTI, but the consequences for colonization and persistence of P. mirabilis in polymicrobial biofilms have not been explored. Here, we characterized the role of biomineralization in regulating the development of P. mirabilis and P. aeruginosa dual-species biofilms. Time-series observations revealed that the dominance of P. mirabilis was synchronized with mineral formation in the biofilm. After 24 h of development, the dual-species biofilm was dominated by P. mirabilis, and the distribution of P. mirabilis biomass was strongly correlated with the mineral fraction of the biofilm. Conversely, dual-species growth without biomineralization yielded strikingly different patterns in the biofilm, with P. aeruginosa dominating the biofilm biomass. These results show that biomineralization is responsible for the increased success of P. mirabilis in the polymicrobial biofilm. Since biofilm biomineralization commonly occurs in diverse clinical, natural and engineered systems, these findings imply that biomineralization could broadly influence the microbial ecology of multispecies biofilms.