Robert Lovelett (Kevrekidis and Avalos labs)
“Modeling, optimization, and control of bioprocesses using optogenetics.”
Microbial cell cultures can be used to produce powerful anti-cancer drugs, precursors for sustainable bioplastics, biofuels for drop-in gasoline substitutes, and many other valuable products. Yet, due partly to process complexity, and partly to a lack of available tools for process optimization (either computational or experimental), these bioprocesses often have low yields and limited economic viability. One challenge is balancing the trade-off between essential mechanisms for cell growth with the demand of producing desired products. Managing this trade-off requires dynamic control of cellular metabolism, and optogenetics provides one promising tool for such real-time control.
Optogenetic circuits can be constructed so that light will activate or inhibit a set of genes or metabolic pathways by regulating transcription. Our group has developed a suite of optogenetic circuits for the yeast S. cerevisiae that respond to blue light. These circuits, depending on design, will either activate a gene when blue light is present, or activate a gene when blue light is turned off. Because they are governed by multistep biochemical reaction pathways that act on different time scales, predicting the dynamic response of the circuits can be challenging. We developed semi-empirical mechanistic models of each of the circuits that enable us to examine the effects of light scheduling on the circuits. Through different light schedules, we can manipulate the expression level of whichever gene is controlled by the circuit. Different light doses, duty cycles, and waveforms were explored to investigate the dynamic behavior of the circuits, helping us understand the performance of a particular circuit, as well as uncover design criteria for selecting optogenetic circuits for particular applications.
With optogenetic circuits in place for regulating metabolism, it remains a challenge to develop optimal control strategies for product production. To address this challenge, we developed a nonlinear ordinary differential equation model describing cell growth, consumption of nutrients, production of desired compounds, and the state of the light-actuated metabolic pathways. We analyzed the model and sought to discover forcing strategies that maximized the yield of desired products. In our case study—continuous isobutanol production in yeast—periodic forcing was determined to be effective at substantially increasing isobutanol production over any reachable steady-state, providing a compelling case for applying optogenetics in metabolic engineering.
Tara TeSlaa (Rabinowitz lab)
“Investigating the role of lactate in organismal metabolism via inhibition of its transport.”
Recent work from the Rabinowitz lab has shown that lactate is a major contributor to organismal energy production. Traditionally, pyruvate produced from glucose is thought to directly enter into the mitochondria in most tissues for efficient energy production utilizing the TCA cycle and the electron transport chain. Work from our lab, however, has shown that there is a rapid exchange between tissue pyruvate and circulating lactate. Because this requires very high expression of lactate related proteins, such as lactate dehydrogenase and monocarboxylate transporters (MCTs), we hypothesize that this high exchange flux plays an important role in organismal metabolism. To disrupt lactate-pyruvate exchange, I have treated mice with an inhibitor of monocarboxylate transporter 1 (MCT1), which is responsible for transport of lactate. MCT1 inhibition results in a 3-fold decrease in lactate-pyruvate exchange. Preliminary results suggest that inhibition of this exchange results in changes in serum and tissue redox ratios as well as hormone secretion.
ICAhN Think & Drink is an interdisciplinary talk series designed to foster new connections. Individuals at all levels and in all departments are invited to join us for two 20 minute talks with complimentary food and refreshments.
See our website (https://icahnthinkanddrink.princeton.edu/)