CAREER: Metabolic 'doping' to enhance production of biochemicals from sustainable C1 feedstocks

About This Grant

Bacteria can grow using a variety of carbon sources, referred to as substrates. Most bacteria grow well on glucose, which contains 6 carbon atoms per molecule (C6). Certain bacteria, referred to as acetogens, can grow on single-carbon (C1) molecules. For example, acetogens can grow on carbon monoxide, or methanol. These compounds can be produced from carbon dioxide. There is a catch; acetogens grow very poorly or not at all in the presence of oxygen. Also, because C1 compounds are not energy-rich, acetogens generally have limited synthetic capabilities. Acetogens could be useful in the renewable production of fuels and chemicals. Achieving this will require reengineering certain aspects of their metabolism. There are two key objectives of this project. One is understanding the regulation of carbon metabolism. The second is to use the insight gained make acetogens a more effective producer of valuable fuels and chemicals. In parallel with these technical objectives, outreach to local high-school students will introduce them to the concept of microbial cell factories. Undergraduates will be provided an opportunity for hands-on experience with bioprocessing in a unit operations lab course. The objective is to equip them for future careers in a robust US bioeconomy. Acetogens are obligate anaerobic bacteria that dwell in energy-poor environments near the thermodynamic limit of life, making a living by converting C1 substrates into acetate through the Wood-Ljungdahl pathway. The high energetic efficiency of this pathway, coupled with recent progress developing advanced genetic tools for these organisms, have made acetogens attractive microbes for the renewable production of biofuels and biochemicals. The major challenge is that, as anaerobes, acetogens growing on a single C1 compound are severely energy limited. Thus, while they can produce low-value compounds, efforts to expand the product profile to higher value products from pathways that demand more cellular energy have been met with minimal success. Some acetogens can simultaneously consume multiple different C1 substrates, or a C1 substrate and sugars. Interestingly, even when the second substrate is provided only at low levels as a ‘dopant’, this can result in drastic improvements in growth rate and productivity. The overall research goals of this CAREER project are to i) understand the metabolic and regulatory mechanisms by which acetogens synergistically leverage multiple substrates simultaneously to overcome growth limitations, then ii) learn how to harness this to direct C1 flux to higher-value products than have previously been possible. An approach that combines isotopic tracer experiments, cofactor perturbation, and transcriptomics will be applied to probe the mechanisms underlying substrate doping. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.