What Biofilm Parameters Are Useful for System Modeling?

Gill Geesey, Center for Biofilm Engineering, Montana State University

Surfaces are ideal niches for the formation and evolution of complex microbial communities. While it has long been recognized that the physical and chemical conditions of the bulk aqueous phase play a significant role in determining which microbial populations are selected for growth on a surface, only recently have we begun to appreciate the importance of the substratum in defining community structure. For example, different mineral phases exposed to the same groundwater develop unique surface-associated microbial communities. This is due to the fact that the mineral surface serves not only as a site for attachment for better access to limiting nutrients in the bulk aqueous phase, but as a nutrient source, itself (i.e., carbon source, electron donor, terminal electron acceptor). Those microbial populations with the genetic capacity to exploit these solid phase resources are more likely to become members of the community that develops on the mineral than populations lacking the capacity to utilize the resource. While we currently are able to identify a few populations that are active in exploiting a particular surface-associated resource, we are far from identifying the roles of the other populations and their interdependencies that define the community. Similarly, we know little of how crystal structure of a particular mineral phase affects the activity and behavior of a surface-associated microbial population. Microscopic analysis has documented many features of surface-associated microbial cell behavior at the individual cell and population level that are amenable to modeling. These include a cell’s identity and phylogenetic relatedness to other phylotypes, attachment rate, detachment rate, growth rate, and physical location with respect to other cells and populations. Now we must integrate molecular biology and microscopy to relate the behavior of cells among many populations of a community and combine this information with fine-scale surface chemistry and bulk aqueous phase chemistry to understand how the surrounding environment controls overall community behavior.