When   Thursday, February 5, 2009   Time   4:00 PM - 5:00 PM  
Where   Technological Instit M345 2145 Sheridan Rd.   map it
Audience   - Faculty/Staff - Student - Public
Contact   Virginia Lorenzo   847-491-5635  
Group   McCormick - Biomedical Engineering Department
More Info   http://www.civil.northwestern.edu/people/packman.html

Aaron Packman, PhD
Associate Professor
Department of Civil & Environmental Engineering
McCormick School of Engineering

Abstract:  Biofilms are surface-attached microbial communities, ubiquitous in nature, and now recognized as the agent of many bacterial infections. Biofilm growth involves numerous feedback processes that modify the local environment, including both chemical distributions and transport conditions. Better understanding of the complex relationship between environmental heterogeneity and biofilm heterogeneity is needed to control biofilm growth on industrial surfaces, maximize rates of favorable chemical transformations in bioreactors, and improve treatment of biofilm-based infections. Here I will describe several recent studies that illustrate how coupling between microbial metabolism, flow-biofilm interactions, and chemical gradients influences biofilm growth and controls net rates of carbon and nutrient consumption in large environmental systems. Incidental stimulation of microbial activity by excess nutrients from fertilizers and wastewater is an extremely pervasive problem, but denitrification – reduction of nitrate to nitrogen gas – can remove excess nitrogen from the water to the atmosphere. Denitrification occurs primarily in biofilms located on or within streambed sediments and other similar surfaces. Hydrodynamic transport processes deliver nitrate from the water column, where large nitrogen concentrations are normally found, to regions where denitrification can occur. Net nitrogen transformation rates thus depend on the interplay of hydrodynamic transport, microbial processes, and the distribution of local chemical conditions within the water column, pore water, and sediments. Similar behavior is also seen in much simpler biofilms growing on artificial surfaces. Recently we have developed a novel planar flow cell that enables biofilm growth, and resulting feedback processes, to be observed under user-selected imposed flow gradients. This system was used to evaluate the effects of nutrient flux and hydrodynamic shear on development of biofilms by Pseudomonas aeruginosa, an opportunistic pathogen that forms biofilm-based infections. Biofilm growth is limited both by transport of nutrients to cells and by shear-induced detachment of cells from the surface. As a result, regular patterns in biofilm growth develop in response to imposed flow gradients. Patterns of P. aeruginosa growth were also substantially modulated by the presence of other biofilm-forming organisms, indicating that modification of the local environment by the microbial consortium plays an important role in development of both biomedical and environmental biofilms.