If there is a beauty of nature more fascinating than the vast variety of her species, it is the immense ability of them to adapt to the least likely livable environments. In this work, we look at the ways biofilms adapt to the harsh conditions of living in fast water flows by numerically studying the biophysical consequences of their special form and possible related function. As a special case, we look at the biofilm streamers, which are clusters of microbial aggregates connected to a tail elongated from the cluster in the direction of the flow. Streamers have a seemingly similar shape to streamlined bodies, a configuration intended to reduce the fluid drag force.
Experimentally it is also observed that the streamers oscillate (flap) in the flow, which suggests that the form may provide higher mixing around the biofilm structure. The question that naturally arises is whether the streamer form is an adaptation mechanism providing a function or a passive formation? Obviously, every familiar form or behavior of an organism, e.g., the streamlined form of sperms, does not enforce an adaptation mechanism in that particular organism, e.g., drag reduction. Therefore, we take these hints and numerically construct a model of a single biofilm streamer to weigh the contribution of the fluid-induced oscillations and the special form on its physical and biological performance.
In the context of this work, a state-of-the-art two-dimensional fluid-structure interaction model of biofilm streamers, coupled with mass transfer of a dissolved substrate is developed. This model numerically calculates the transient deformation of the streamer with simultaneous substrate transport and uptake using moving mesh finite element method.
We show that the streamlined form of the biofilm streamers reduces the fluid forces acting on the structure significantly. In addition, the periodic deformation (oscillation) of the flexible body increases the substrate transport into the biofilm compared to the static (immobile) case. Overall, we propose that the special morphology of the streamers, regardless of the formation process, is a successful strategy in reducing the fluid forces biofilms experience, and increases their overall biological fitness by providing relatively higher substrate transport especially in the tail section.