Understanding Biofilm Formation in Co-Cultures of Candida Albicans and Candida Glabrata

Abstract

Candida spp. are commensal opportunistic fungal pathogens that often colonize and infect mucosal surfaces of the human body. Candida, along with other microbes in the microbiota, generally grow as biofilms in a polymicrobial environment. Due to the nature of cellular growth in a biofilm (such as production of a protective extracellular matrix) and the recalcitrance of biofilms, infections involving biofilms are very difficult to treat with antibiotics and perpetuate the cycle of infection. The two most commonly isolated Candida spp. from Candida infections are Candida albicans and Candida glabrata, and the presence of both of these species results in increased patient inflammation and overall biofilm formation. In this work, we investigate the interspecies interactions between C. albicans (Ca) and C. glabrata (Cg) in co-culture through understanding biofilm formation, transcriptomic analysis, and the involvement of the quorum-sensing molecule farnesol in biofilm formation. We report that biofilm formation in co-culture populations of Ca and Cg is dependent on the relative starting concentrations of each species, with the highest biofilm formation in a ratio of Ca:Cg 1:3. Confocal microscopy analysis revealed increased biofilm heterogeneity and Ca hyphae length in co culture biofilm compared to mono-culture biofilms. Several genes involved in Ca adhesion (HWP1 and ALS3) were up-regulated in Ca:Cg 1:3 co-culture biofilms and there was also an increase in resistance to the antifungal drug caspofungin in co-culture biofilms. Next, we utilized transcriptomic analysis to further understand Ca:Cg interspecies interactions within co-culture biofilms. We found that, in co-culture biofilms, lipid and cell wall biosynthesis genes were significantly down-regulated and perturbed in both Ca and Cg, and it was demonstrated that cell wall lipid content is increased in co-culture biofilms in C. albicans via confocal microscopy. Finally, we investigated the relationship and mechanisms of farnesol with C. glabrata cultures and also the impact of farnesol on co culture biofilm formation. Results show possible Cg sequestration of farnesol and that there are other factors likely at play during co-culture biofilm formation that leads to increased biofilm formation, especially in the highest biofilm former Ca:Cg 1:3.