Tunable Double Yielding in Bacterial Biofilms

Biofilms are populations of bacteria surrounded by diverse extracellular polymeric substances that they excrete. Typically found in warm, wet environments such as water filtration plants or hospital catheters, biofilms can decrease efficiency and cause infections. The behavior of Staphylococcus epidermidis spherical bacteria in a biofilm was found to be rheologically similar to colloidal gels, which can experience a double yielding phenomenon under shear strain. By using gene deletion and chemical inhibition, the microstructural mechanisms for the yielding behavior were deduced. Deletion of srtA, which encodes sortase A, produced a biofilm that exhibited only single yielding and lower yielding strains. The osmotic pressure of the growth environment also had a more profound effect on the biofilms with the srtA deletion. Other clinically relevant biofilms also experienced mechanical effects with srtA gene deletion. Sortase A is a known antivirulence target as an enzyme involved in anchoring surface proteins to the cell wall and interfacing with the polysaccharide matrix; our work highlights the mechanical role sortase A plays in influencing biofilm removal or bacterial virulence. The complex biofilm network also provides a new basis for understanding molecular motivations of mechanical behavior.