CEE Graduate Seminars 2012
Friday, January 6, 2012
D221 Thornton Hall 2:00 PM
Using Continuous-Flow Chemostat Bioreactors to Investigate Microbial Metabolism
Kurt R. Rhoads
Continuous-flow chemostat bioreactors offer several advantages over batch reactors because they allow for greater control. I will present two novel applications of chemostat bioreactors to investigate microbial metabolism. In the first part, I will show how continuous-flow in situ bioreactors can improve predictions of a model fluorinated repellent, N-ethyl perfluorooctane sulfonamidoethanol (N-EtFOSE), in wastewater treatment plants. Fluorinated repellents and their degradation products are suspected carcinogens and have been linked to reproductive effects in humans. We measured the N-EtFOSE biotransformation rate in bypass reactors installed at a full-scale municipal treatment plant to approximate the conditions in a typical aeration basin. N-EtFOSE biotransformed 11-25% slower in the in situ tests compared to batch tests, indicating that changes in reactor conditions during batch tests may lead to overprediction of biotransformation rates. Using a fate model, we predict that 71% of N-EtFOSE entering a sewer will be stripped to the atmosphere, compared with 18% that will be biotransformed. The results of the model suggest that N-EtFOSE discharged to sewers may be atmospherically transported and may contribute to fluorochemical contamination remote regions, such as the Arctic. For the second topic, I will discuss how continuous-flow bioreactors can be used to understand regulatory processes in algae grown for biofuel applications, potentially leading to strains with enhanced bioaccumulation capacity. We investigated changes in lipid bioaccumulation enzymes and other indicator proteins in the model alga, Chlamydomonas reinhardtii, under low nitrogen-, phosphorus-, or sulfur- conditions. By using continuous-flow bioreactors, we maintained steady-state conditions and eliminated residual proteins. The cells grown under nitrogen-limited conditions had lipid concentrations four times that of control cells. Cellular proteins were digested, labeled with an isobaric tag, and analyzed using high-resolution liquid chromatography/tandem mass spectrometry. One lipid biosynthesis enzyme, 3-ketoacyl-CoA synthetase, was significantly upregulated in the nitrogen-limited cells compared to controls. This enzyme could potentially be genetically engineered to increase algal yields. Another protein identified in nitrogen-limited cells, major lipid droplet protein, could be used as an indicator for lipid accumulation.
Kurt Rhoads received his M.S. and Ph.D. degrees in Civil & Environmental Engineering from Stanford University, where he was a NIH Biotechnology and EPA STAR graduate fellow. He was a postdoctoral associate at Cornell University and is now a postdoctoral associate at Duke University. Dr. Rhoads also spent two years as an engineering consultant in the Washington, D.C. area working in bioremediation.
The Civil Engineering seminar series is open to the University community.
Civil Engineering undergraduate students are especially invited to attend.