Bacteria utilize chemical and mechanical mechanisms to sense their environment, to survive hostile conditions. In mechanical sensing, intra-bilayer pressure profiles change due to deformation induced by the adhesion forces bacteria experience on a surface. Emergent properties in mono-species Streptococcus mutans biofilms, such as extracellular matrix production, depend on the adhesion forces that streptococci sense. Here we determined whether and how salivary-conditioning film (SCF) adsorption and the multi-species nature of oral biofilm influence adhesion force sensing and associated gene expression by S. mutans. Hereto, Streptococcus oralis, Actinomyces naeslundii, and S. mutans were grown together on different surfaces in the absence and presence of an adsorbed SCF. Atomic force microscopy and RT-qPCR were used to measure S. mutans adhesion forces and gene expressions. Upon SCF adsorption, stationary adhesion forces decreased on a hydrophobic and increased on a hydrophilic surface to around 8 nN. Optical coherence tomography showed that triple-species biofilms on SCF-coated surfaces with dead S. oralis adhered weakly and often detached as a contiguous sheet. Concurrently, S. mutans displayed no differential adhesion force sensing on SCF-coated surfaces in the triple-species biofilms with dead S. oralis, but once live S. oralis were present S. mutans adhesion force sensing and gene expression ranked similar as on surfaces in the absence of an adsorbed SCF. Concluding, live S. oralis may enzymatically degrade SCF components to facilitate direct contact of biofilm inhabitants with surfaces and allow S. mutans adhesion force sensing of underlying surfaces to define its appropriate adaptive response. This represents a new function of initial colonizers in multi-species oral biofilms.

细菌利用化学和机械机制来感知其环境，以在恶劣的条件下生存。在机械感测中，双层内压力分布会由于细菌在表面上经历的粘附力而引起的变形而发生变化。单种变异链球菌生物膜的新兴特性，例如细胞外基质的产生，取决于链球菌的粘附力。在这里，我们确定唾液调节膜（SCF）的吸附以及口腔生物膜的多物种特性是否以及如何影响变形链球菌的粘附力感测和相关基因表达。迄今为止，口头链球菌，内生放线菌和变形链球菌在不存在和吸附SCF的情况下，它们在不同的表面上共同生长。原子力显微镜和RT-qPCR用于测量变形链球菌的粘附力和基因表达。在SCF吸附后，固定的粘附力在疏水性上降低，而在亲水性表面上增加到大约8 nN。光学相干断层扫描显示，死死的口腔链球菌在SCF涂层表面上的三物种生物膜粘附力很弱，并且经常以连续的薄片形式脱落。同时，变形链球菌显示在与死三重物种的生物膜SCF-涂层表面无差分的粘附力感测口腔链球菌，但一旦活口腔链球菌存在变异链球菌粘附力传感和基因表达的排名与在没有吸附SCF的情况下在表面上的排名相似。最后，活的口腔链球菌可酶降解SCF组分，以促进生物膜居民与表面的直接接触，并允许变形链球菌对下层表面的粘附力进行感应，以定义其适当的适应性反应。这代表了最初的定居者在多种物种口腔生物膜中的新功能。