Communication in biofilms between different species: Candida albicans and Pseudomonas aeruginosa

Candida albicans, a polymorphic fungus, and Pseudomonas aeruginosa, a Gram-negative bacterium, are two opportunistic pathogens that can cause serious infections in different sites within the human host. Growing in a particular lifestyle called biofilm they are well protected against the human immune system compared to conspecific in planctonic growth. Therefore these organisms are used as model systems for fungal and bacterial biofilm research. Biofilms are structured communities of microorganisms enclosed in a selfproduced polymeric matrix and adherent to an inert or living surface. One of the hallmarks required for the formation of biofilms is the so-called quorum sensing modulated by specific molecules which regulate this developmental process via defined signal cascades. Farnesol is a quorum sensing molecule used by C. albicans which inhibits fungal biofilm formation. It is mediated through a two-component signal transduction histidin kinase Chk1p. In P. aeruginosa N-3-oxo-dodecanoyl-L-homoserine lactone (3OC12HSL) represents a quorum sensing molecule. It acts as a positive regulator via LasR. Both molecules, which contain twelve-carbon backbones, repress C. albicans filamentation without altering its growth rate. To see how the organisms communicate with each other in biofilms a method to quantify the influence of quorum sensing molecules on C. albicans and P. aeruginosa biofilms was used. To visualize the interaction between both organisms mixed biofilms have been studied. Reporter strains have been constructed to analyse the influence of quorum sensing molecules during biofilm formation. Our results indicate that 3OC12HSL has impact on C. albicans biofilm formation and biofilms of P. aeruginosa are manipulated by farnesol.