Kasetty, S. | Search bioRxiv

bioRxiv2021

Differential surface competition and biofilm invasion strategies of Pseudomonas aeruginosa PA14 and PA01

Pseudomonas aeruginosa strains PA14 and PAO1 are among the two best characterized model organisms used to study the mechanisms of biofilm formation, while also representing two distinct lineages of P. aeruginosa. Our previous work showed that P. aeruginosa PA14 and PAO1 use distinct strategies to initiate biofilm growth. Using differentially-labeled strains and microfluidic devices, we show that PAO1 can outcompete PA14 in a head-to-head competition during early colonization of a surface, can do so in constant and perturbed environments, that this advantage is specific to biofilm growth and requires production of the Psl polysaccharide. In contrast, the P. aeruginosa PA14 exhibits a competitive fitness advantage when invading a pre-formed biofilm and is better able to tolerate starvation than PAO1 in the biofilm context. These data support the model that while P. aeruginosa PAO1 and PA14 are both able to effectively colonize surfaces, these strains use distinct strategies that are advantageous under different environmental settings. ImportanceRecent studies indicate that P. aeruginosa PAO1 and PA14 use distinct strategies to initiate biofilm formation, with PAO1 committing to the surface through a processive mode of attachment, while PA14 uses a non-processive surface engagement strategy. We investigated whether their respective colonization strategies impact their ability to effectively compete under different biofilm-forming regimes. Our work shows that these different strategies do indeed impact how these strains colonize the surface: PAO1 dominates during colonization of a naive surface, while PA14 is more effective in colonizing a pre-formed biofilm or withstanding starvation conditions. These data suggest that even for very similar microbes there may be distinct strategies to successfully colonize and persist on surfaces during the biofilm life cycle.

microbiology↗

bioRxiv2020

Pseudomonas aeruginosa and Candida albicans both accumulate greater biomass in dual species biofilms under flow

Spatially structured communities of microbes - biofilms - are widespread in nature, and biofilm-dwelling microbes often respond to their environments in ways that are different from their planktonic counterparts. Further, most natural biofilms are multi-species mixtures of microorganisms; the ecology of intra- and inter-species interactions in these consortia, and the resulting effects on total community properties, are often not well understood. A common site of polymicrobial biofilm infections is the lungs of patients with cystic fibrosis (CF). CF is a genetic disorder in humans that leads to colonization of the lungs by a variety of microorganisms, including Pseudomonas aeruginosa and Candida albicans. These opportunistic pathogens are frequently co-isolated from infected lungs, in addition to other infection sites including urinary and intravenous catheters. To study how these microbes behave together in biofilms, we developed a modified artificial sputum medium that is optically clear for use with microfluidic culture. In addition, we engineered strains with optimized fluorescent protein expression constructs allowing for single-cell resolution confocal microscopy. Using these tools and recently developed methods for spatial analysis of 3-D image data, we found that both P. aeruginosa and C. albicans display increased biovolume accumulation in multi-species biofilms relative to single-species biofilms. This pattern did not occur in planktonic co-culture and was thus specific to the biofilm environment. Interestingly, introduction of P. aeruginosa supernatants over dual-species biofilms strongly reduced C. albicans biovolume. This suggests that products that accumulate in batch culture were still inhibitory to C. albicans under a flow regime, but that they their de novo production in mixed species biofilms was not sufficient to inhibit C. albicans biofilm accumulation. Altogether our results indicate a critical impact of flow environment for the outcome of polymicrobial interactions and the need for high-resolution analysis of such communities in future work.

microbiology↗