Guanghong Zeng, iNANO, Aarhus University, Aarhus C, Denmark, Tal Duanis-Assaf, Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem, Israel,Rikke Louise Meyer, iNANO, Aarhus University, Aarhus C, Denmark, Meital Reches,  Institute of Chemistry, Hebrew University of Jerusalem, Jerusalem, Israel, Doron Steinberg,  Biofilm Research Laboratory, Institute of Dental Sciences, Faculty of Dental Medicine, Hebrew University-Hadassah, Jerusalem, Israel

Many bacteria in biofilm surround themselves by an extracellular matrix composed mainly of extracellular polysaccharide (EP), proteins such as amyloid-like fibers (ALF) and nucleic acids. While the importance of EP in attachment and acceleration of biofilm by a number of different bacterial species is well established, the contribution of ALF to attachment in multispecies biofilm remains unknown. The study presented here aimed to investigate the role of TasA, a precursor for ALF, in cell-cell interactions in dual-species biofilms of Bacillus subtilis and Streptococcus mutans. Expression of major B. subtilis matrix operons was significantly up-regulated in the presence of S. mutans during different stages of biofilm formation, suggesting that the two species interacted and modulated gene expression in each other. Wild-type B. subtilis expressing TasA adhered strongly to S. mutans biofilm, while a TasA-deficient mutant was less adhesive and consequently less abundant in the dual-species biofilm. Dextran, a biofilm polysaccharide, induced aggregation of B. subtilis and stimulated adhesion to S. mutans biofilms. This effect was only observed in the wild-type strain, suggesting that interactions between TasA and dextran-associated EP plays an important role in inter-species interactions during initial stages of multispecies biofilm development.