Special Chemical Engineering Seminar
Single-carbon (C1) substrates, such as methane, methanol, formate, and synthesis gas are attractive feedstocks for biochemical processes, as they are widely available, can be produced renewably, and do not compete with food supply. However, their use in industrial bioprocesses remains limited, primarily because microbes that utilize these substrates are poorly characterized biochemically, and limited tools exist for their genetic modification. This leaves the metabolic engineer with a choice: to develop genetic tools to enable engineering in the desired host, or to import the relevant catabolic pathway into a more tractable organism, such as Escherichia coli. In this seminar, I will explore the merits and challenges of both options, using examples from my work on developing strains for the conversion of synthesis gas and methanol into chemicals and fuels.
Clostridium ljungdahlii is an acetogen that grows autotrophically on synthesis gas (CO, H2, and CO2) using the Wood-Ljungdahl pathway, and is a promising candidate for renewable biofuel and biochemical production from gasified biomass or waste industrial gases. In the first section of the talk, I will describe the metabolic engineering of this microbe to produce 3-hydroxybutyrate, a platform molecule used for the production of vitamins, antibiotics, and flavor compounds. I will focus on the development of a CRISPR-interference (CRISPRi) system for the inducible knockdown of competing pathway genes, insights into the complexity of acetogen metabolism, and on new strategies to overcome thermodynamic limitations on product yield.
To explore the alternative approach of importing a single-carbon catabolic pathway into a tractable host, in the second section of the talk I will discuss engineering E. coli to metabolize methanol, a plentiful C1 feedstock with a well-defined catabolic pathway. I will describe a systematic approach based on quantitative metabolomics, isotopic tracer experiments, and small-molecule inhibitors that was used to establish and eliminate the main bottlenecks in the engineered pathway, and ongoing work using evolutionary approaches to further improve pathway flux.