Mixed Population Biofilms

Abstract

Multiple species biofilms comprise mixed bacterial populations within an extracellular polymeric matrix bound to a substratum. These attached mixed cultures are subject to interactions such as symbiosis or competition for either space or a common substrate; such interactions are directly or indirectly influenced by a myriad of variables associated with the surrounding environment. Spatial distributions of microbial populations are everchanging under the selection pressures exerted by processes such as: (a) exchange of bacterial species with the bulk liquid phase; (b) the relative efficiency of each species to metabolize their limiting substrate(s) into viable cell mass and non-viable extracellular polymers; (c) transport of limiting substrates and essential nutrients by molecular and convective transfer mechanisms; and (d) biofilm removal processes brought on by either physiological mechanisms (sloughing) or as a result of prevailing hydrodynamics (shear-related detachment). Evolution of spatial distributions of species within a biofilm can affect the biofilm’s overall performance in specific situations (e.g., natural purification of contaminated surface- or ground-waters, in situ bioremediation of xenobiotics, fate of recombinant DNA sequences and host microbes in the open environment, specific biofilm wastewater treatment systems, and specialty bioconversions). Consequently, it is critical to know how the ever-changing attached population distributions can affect overall system performance in order to better design, interpret, and operate biofilm systems.