Dual-Species Biofilms: Biomass, Viable Cell Ratio/Cross-Species Interactions, Conjugative Transfer.

Biofilms as a form of adaptation are beneficial for bacterial survival and may be hot spots for horizontal gene transfer, including conjugation. The aim of this research was to characterize the biofilm biomass, viable cell ratios and conjugative transfer of the pOX38 plasmid, an F-plasmid derivative, from the N4i pOX38 strain (donor) into a uropathogenic DL82 strain (recipient) within dual-species biofilms with one of the following opportunistic pathogenic bacteria: , or . Dual-species biofilms of with or but not were more massive and possessed more exopolysaccharide matrix compared to single-species biofilms of donor and recipient cells. Correlation between biofilm biomass and exopolysaccharide matrix was rs = 0.888 in dual-species biofilms. In dual-species biofilm with the proportion of was the highest, while in the biofilm with and , the was less abundant. The conjugative frequencies of plasmid transfer in dual-species biofilms of with and were reduced. A decrease in conjugative frequency was also observed when cell-free supernatants (CFSs) of and were added to the conjugation mixture. Further, the activity of the autoinducer AI-2 in the CFSs of the conjugation mixture was reduced when bacteria or CFSs of and were added to the conjugation mixture. Hence, the intercellular and interspecies interactions in dual-species biofilms depend on the partners involved.