The role of shear dynamics in biofilm formation

There is growing evidence that individual bacteria sense and respond to changes in mechanical loading. However, the subtle responses of multispecies biofilms to dynamic fluid shear stress are not well documented because experiments often fail to disentangle any beneficial effects of shear stress from those delivered by convective transport of vital nutrients. We observed the development of biofilms with lognormally distributed microcolony sizes in drinking water on the walls of flow channels underflow regimes of increasing complexity. First, where regular vortices induced oscillating wall shear and simultaneously enhanced mass transport, which produced the thickest most extensive biofilms. Second, where unsteady uniform flow imposed an oscillating wall shear, with no enhanced transport, and where the biomass and coverage were only 20% smaller. Finally, for uniform steady flows with constant wall shear where the extent, thickness, and density of the biofilms were on average 60% smaller. Thus, the dynamics of shear stress played a significant role in promoting biofilm development, over and above its magnitude or mass transfer effects, and therefore, mechanosensing may prevail in complex multispecies biofilms which could open up new ways of controlling biofilm structure.

Automated summary

There is evidence that individual bacteria can sense and respond to changes in mechanical loading. However, the specific responses of multispecies biofilms to dynamic fluid shear stress have not been well documented. In this study, the development of biofilms in drinking water on flow channel walls was observed under different flow regimes. The results showed that the dynamics of shear stress played a significant role in promoting biofilm development, beyond just the magnitude or mass transfer effects. This finding suggests that mechanosensing may be important in complex multispecies biofilms and could lead to new ways of controlling biofilm structure.