College of Agriculture & Life Sciences,
Chemical & Biomolecular Engineering Department, Microbiology Department, Biomanufacturing Training & Education Center,
Nano Research Area
- Nano-Energy & Environment
Dr. Michael Flickinger's research focuses on biocatalytic coatings, nanostructured bioreactive materials, bioprocess intensification and miniaturization (BIM), coating/photo and microchannel bioreactor design, combined with microbial metabolic engineering. We study how to engineer high intensity thin coating biocatalysts. Our coating microstructure, bioreactive ink and bioreactor research is in Chemical and Biomolecular Engineering; our metabolic engineering studies are in the Dept. of Microbiology. We use cryogenic SEM, laser scanning confocal microscopy and other methods to characterize nanostructured coatings containing living microbes as well as biochemical techniques to measure their activity. Our first review article "Painting and Printing Living Bacteria: Engineering Nanoporous Biocatalytic Coatings to Preserve Microbial Viability and Intensify Reactivity" was published in Biotechnology Progress (23, 2-17, 2007). Current research includes: engineering polymer adhesion, coating nanoporosity and preservation of microbial viability in coatings and ink-jet inks, advanced coating methods, photoreactive coatings and microbial engineering to enhance biocatalyst intensity. Several model systems are being investigated.
It has been a goal of biochemical engineers to use photo reactive microorganisms to generate energy, such as hydrogen gas (H2), from sun-light. However previous approaches have been limited by low reactivity, low illuminated surface to volume ratio, and saturation at high light intensity resulting in only a small fraction of the solar radiation incident on photosynthetic microbes being converted to metabolic energy to generate H2. Our group recently reported the reactivity of ~60µm thick coatings of non-growing anoxic Rhodopseudomonas palustris that use nitrogenase to produce H2 when illuminated (Gosse et. al., 2007. Biotechnol. Prog. 23, 124-130). Coatings of nitrogen-limited Rps. palustris produce H2 at a constant rate for >4,000 hours when provided with acetate. We are engineering Rps. palustris to overcome light saturation in order to optimize the rate of H2 production by altering light harvesting pigments to increase the efficiency of photon capture. We combine mutants with complementary light adsorption in multi-layer coatings. Modeling of coating optical properties (adsorption, scattering, reactivity) is another approach we use. These investigations are being extended to nanoporous polymer coatings of Chlamydomonas reinhardtii that utilizes hydrogenase under sulfur limitation anaerobically to generate H2 from sunlight and water.
In addition to photoreactivity, biocatalytic coatings and biocatalytic membranes can also concentrate microorganisms at a phase boundary between a gas and a liquid. We have developed reactive adhesive nanoporous latex coatings of Gluconobacter oxydans, a strict aerobe, for high intensity whole cell biooxidations (Fidaleo et. al., 2006. Biotechnol. Bioeng. 95, 446-458). The reactivity of these 20µm G. oxydans coatings which oxidize D-sorbitol to L-sorbose is orders of magnitude higher than previously reported. A diffusion reaction model was developed to simulate the reactivity of coatings of G. oxydans as a function of thickness and biocatalytic activity. This model is being used to simulate the intensity of G. oxydans coatings in channels with intermittent gas-liquid Taylor slug flow and design a prototype microchannel bioreactor. New methods are being developed to coat channels with bilayer coatings with minimal difusion limitations. Ink-jet deposition is being used to rapidly evaluate polymer emulsions, drying conditions and coating microstructure for optimal reactivity and nanoporosity. This project will generate important results for development of multiphase microchannel bioreactors and the use of microorganisms in microluidic devices.