All organisms throughout the tree of life sense and respond to their surface environments. To discriminate from among mucosal surface environmental cues, we grew Streptococcus gordonii biofilms over night at 37C on surfaces coated with the salivary mucin MUC5B, or a low density protein fraction derived from human saliva. Overall design: Biofilms of Streptococcus gordonii were grown from an initial OD600nm = 0.1 in BHI broth for 16 to 18 h at 37°C and 5% CO2 on MUC5B- or LDP-coated plates. Sheer was applied by placing samples on a rocker during the overnight incubation period.