Flexible Survival Strategies of Pseudomonas aeruginosa in Biofilms Result in Increased Fitness Compared with Candida albicans

Abstract

The majority of microorganisms persist in nature as surface-attached communities often surrounded by an extracellular matrix, called biofilms. Most natural biofilms are not formed by a single species but by multiple species. Microorganisms not only cooperate as in some multispecies biofilms but also compete for available nutrients. The Gram-negative bacterium Pseudomonas aeruginosa and the polymorphic fungus Candida albicans are two opportunistic pathogens that are often found coexisting in a human host. Several models of mixed biofilms have been reported for these organisms showing antagonistic behavior. To investigate the interaction of P. aeruginosa and C. albicans in more detail, we analyzed the secretome of single and mixed biofilms of both organisms using MALDI-TOF MS/MS at several time points. Overall 247 individual proteins were identified, 170 originated from P. aeruginosa and 77 from C. albicans. Only 39 of the 131 in mixed biofilms identified proteins were assigned to the fungus whereby the remaining 92 proteins belonged to P. aeruginosa. In single-species biofilms, both organisms showed a higher diversity of proteins with 73 being assigned to C. albicans and 154 to P. aeruginosa. Most interestingly, P. aeruginosa in the presence of C. albicans secreted 16 proteins in significantly higher amounts or exclusively among other virulence factors such as exotoxin A and iron acquisition systems. In addition, the high affinity iron-binding siderophore pyoverdine was identified in mixed biofilms but not in bacterial biofilms, indicating that P. aeruginosa increases its capability to sequester iron in competition with C. albicans. In contrast, C. albicans metabolism was significantly reduced, including a reduction in detectable iron acquisition proteins. The results obtained in this study show that microorganisms not only compete with the host for essential nutrients but also strongly with the present microflora in order to gain a competitive advantage. Molecular & Cellular Proteomics

Interspecies competition triggers virulence and mutability in Candida albicans–Pseudomonas aeruginosa mixed biofilms

“…As previously reported by Purschke et al (2012), we observed a significant increase in the production of iron-regulated proteases by P. aeruginosa in coculture supernatants, including PrpL, PasP, AprA and a hypothetical protein zinc-protease, PA0572 (Supplementary Table S3) (Wilderman et al, 2001;Marquart et al, 2005). These proteins are known for their strong proteolytic activities, which are responsible for rupturing tight junctions in the epithelium, leading to tissue invasion and bacterial spreading (Azghani et al, 1993).…”

“…In the context of microbial interactions, iron competition in Pseudomonas has been studied, and the role of the pyoverdine siderophore produced by Pseudomonas species has been clearly demonstrated in competition with fungus and bacteria (Loper and Buyer, 1991;Harrison et al, 2008). For example, Purschke et al (2012) demonstrated that P. aeruginosa increases pyoverdine production in response to iron competition with C. albicans in mixed biofilms. Consistent with these findings, we identified proteins with known roles in iron uptake mediated by siderophores that were upregulated in P. aeruginosa in mixed biofilms in response to the interaction with C. albicans.…”

A Metaproteomics Approach to Elucidate Host and Pathogen Protein Expression during Catheter-Associated Urinary Tract Infections (CAUTIs)

“…Our findings are in good agreement with earlier studies demonstrating an increase of iron-uptake mechanisms on the transcriptome level when opportunistic patho- gens were cultivated in urine (E. coli, P. mirabilis), in the urinary tract (E. coli) or on AUM agar plates (P. aeruginosa) (18 -21). In an infected bladder environment the availability of iron is even more restricted by competition for iron in multispecies biofilms (84) and the presence of siderophore-and iron-binding proteins such as NGAL and lactoferrin in the urine representing the nutritional immunity (Fig. 5, supplemental File S6) (85).…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…Some primary surface colonizers may inhibit colonization by other and/or later-arriving taxa (638), and this competition may be quite subtle. P. aeruginosa in multispecies microbial biofilms increases the production of organic iron chelators, siderophores, in response to increasing Fe scarcity, thus enjoying a competitive advantage over other microorganisms (639)(640)(641). Although this strategy may increase the ability of P. aeruginosa to sequester iron and thus outperform other microorganisms, it also produces the opportunity for siderophore nonproducers to benefit.…”