Fungal biofilmsBiodegradationAnthraquinone dyeBacterial stressPseudomonas fluorescensBacillus licheniformis

White-rot fungi are efficient degraders of lignin whose extracellular enzymes have a potential to degradeorganopollutants. In natural conditions these fungi enter into interactions with other organisms, which may affecttheir biodegradation capacity. The aim was to investigate the ability of Pleurotus ostreatus to form stable biofilmsand to test the capacity of the fungus to degrade Remazol Brilliant Blue R in mixed cultures with bacteria. Bacterialcounts were determined to see the behavior of the bacterium in the mixed culture with the fungus. In axenic conditions,the homogenized fungal mycelium was able to form an active biofilm which quickly degraded the dye. Theaddition of Pseudomonas fluorescens or Bacillus licheniformis bacteria at 106 CFU?mL?1 did not affect the decolorizationrate by 7-d-old fungal biofilms where the decolorization rate reached 90%. In contrast, when fragments of thefungal mycelium were used for inoculation to pre-formed biofilm of P. fluorescens, the biofilm was allowed to developfor one week's time, no decolorization of RBBR was observed and low activities of MnP and laccase were detected.The use of agar disks covered with fungal mycelium for the inoculation to pre-formed biofilm of P. fluorescens resultedin a fully developed biofilm that decolorized RBBR with similar efficiency as the pure P. ostreatus. The differencebetween the agar-disk- and homogenized-mycelium inoculated fungal biofilms was corroborated by the measurementof total fungal biofilm biomass that was 6-fold lower in the latter biofilm. Capability of the fungus to overcomethe competition of the bacterial biofilm thus depended on the type of fungal growth centres, where intact hyphaewere superior to the fragments of mycelium. A similar effect was not observed with the biofilms of B. licheniformiswhere the bacterial growth was less massive. The ability of P. ostreatus biofilms to resist massive bacterial stress wasdemonstrated.