Our research group spans a wide range of applied biotechnology projects, that is highly experimental involving both genetic engineering and bioreactor engineering. The areas are generally described below, where much more specific information can be found at the CurtisLab website.
Algae: We have been conducting algae biofuel work for nearly ten years. A major focus is on the design and operation of photobioreactor systems which requires manipulating availability of light, CO2 and other nutrients. When algae are grown at very high density, this introduces limitations of light penetration, and gas exchange. We have shown that a major constraint is controlling the pH of the media as the algae utilize nitrogen sources, and are developing control strategies to feed nutrients based on growth models. We are particularly excited about work with an algae that makes a C30+ hydrocarbon(Botryococcus braunii) rather than making fats used in biodiesel. Our oil productivities with this algae have outpaced other algae since they produce the oil without imposing nutrient limitations.
Cellulosic: The cellulose of plants is a polymer of glucose, which is hard to break down (by design). None-the-less, there are microorganisms that can “chew on sticks” and produce fuels. Rather than trying to have a single &ldquopsuper bug” that both breaks down cellulose and makes fuel, we have taken a “division of labors” approach. We have shown that we can engineer a symbiosis between a cellulose degrader … and a fuel producer using oxygen transport limitations. This symbiosis approach has been able to produce more fuel than either organism alone. This work involves both improving both organisms including the metabolic engineering of new fuel pathways into the “fuel partner.”
Electrofuels: This project is based on organisms that can consume H2 and O2 that is generated by electrolysis of water. We have successfully moved the algae hydrocarbon pathway above into a bacteria that can “fix CO2” in the dark using H2 and O2 (autotrophic). This requires testing a large number of genetic constructs to overcome rate-limiting steps for fuel production. In addition, we have constructed a wide variety of bioreactor systems to feed these gas mixtures and allow for monitoring growth with integrated optical sensors.
Plant Propagation: It is possible to take a generic plant cell and induce it to become an embryo that can then mature to plant. Since this happens without fertilization, it is called &ldquopsomatic embryogenesis.” This ability to massively clone plants introduces an alternative way to rapidly produce superior plants that are for example resistant to disease, drought, and other environmental stresses. Our current work focuses on the chocolate tree (Theobroma cacao) because of its world-wide economic importance—particularly in developing countries near the equator where cacao is grown. We developed a way to deliver DNA to plants using a modified bacteria. This bacteria can deliver genetic switches (transcription factors) to turn on the process of somatic embyrogensis. We seek to not only discover and understand this process of plant development, but implement this in bioreactor systems. We have developed bioreactors that do not “drown” plants by only intermittently submerging the plants in sterile nutrient solutions. The ultimate goal of this work is to more generally facilitate plant improvement. We have a collaboration with a researcher in Nigeria to see if we can extend this work to the food crop yam (not sweet potato) which feeds hundreds of thousands of people in developing countries.
Protein Production in Plants: By using our DNA delivery bacteria, we can slip DNA into plant cells which will result in the production of protein (without actually integrating the DNA into the chromosome). This is called “transient expression.” We have used this method in the past to express proteins for pathogenic E.coli vaccination of animals. Currently we are testing the ability of this system to express “difficult” proteins including the protein responsible for allowing plant cells to expand (expansin) with the hope that it might be useful towards biomass to biofuels application. We are also working with a materials scientist to express a “squid protein” that has amazing properties of being able to be “melted and molded” as well as a great glue that works under water.
Membrane Protein Expression: Membrane proteins are critically important for moving good stuff in (and keeping bad stuff out) of cells. As a result, many diseases are associated with problems of membrane protein function. In addition, membrane proteins also therefore represent potential ways to separate and purify metabolites. We are using a photosynthetic bacteria (Rhodobacter) that has the rather unique characteristic of being a prokartyotic organism that is easy to genetically engineer, while having large amounts of intracellular membranes (normally used for photosynthesis). We have shown we can produce large quantities of FUNCTIONAL membrane proteins (not mis-folded or precipitated) that can be used for various studies of solute transport. Since the expression of important medical proteins has not been successful in many other systems, there is an interest in testing and scaling up the applicability of this system for numerous collaborateors at Penn State and other medical schools. Working with Dr. Manish Kumar, we can facilitate functional testing and measurement of the rates of transport of through these trans-membrane transporters. This provides quantitative capabilities associated with the understanding of the roles of these proteins in disease (or separation applications).