Case study: biofilms

Most microorganisms in nature spend their existence attached to surfaces in communities called biofilms. Organisms in biofilms are largely responsible for most biodegradation that occurs naturally, yet little is known about the physiology of organisms in biofilms and how the interaction among organisms in biofilms leads to degradation of toxic organics or accumulation of heavy metals. Furthermore, there are relatively few tools to study biofilms. To that end, we have developed several experimental tools to examine biofilms non-destructively and to visualize the interactions between two or more organisms in a biofilm. These tools include bioreactors for biofilm growth on surfaces that can be imaged readily by soft X-ray microscopy or confocal microscopy and broad-host-range vectors for production of various green fluorescent proteins in the various organisms in a multi-species biofilm. We have used these tools to examine the interaction of two Pseudomonads in a biofilm, each of which degraded a different organic contaminant. We found that only with both organisms present would either organism survive in the presence of both organics and that the morphology of the dual-species biofilm changes with the concentration of the organics. The articles describing these studies were the first to document the use of multiple fluorescent proteins to image multiple organisms in a biofilm.