Pseudomonas aeruginosaandCandida albicansboth accumulate greater biomass in dual species biofilms under flow

Abstract

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.

Probing mutual interactions between Pseudomonas aeruginosa and Candida albicans in a biofabricated membrane-based microfluidic platform

“…10 The bacterium, Pseudomonas aeruginosa (Pa), and the polymorphic fungus, Candida albicans (Ca), are commonly found together. 11 Studies have shown that both physical contact and intercellular signalling by diffusible factors contribute to the interactions and behaviors of these bacteria-yeast communities. Fig.…”