(344e) Metabolic Engineering of Cyanobacteria and Methanotrophs for Sustainable Chemical Production

Sustainable chemical production requires full utilization of waste streams, both to circularize carbon and to access inexpensive or free feedstocks. Two critical waste carbon streams are CO₂ and methane, both potent greenhouse gasses that are produced from agricultural, industrial, and energy process. Biological fixation of CO₂ and methane can be performed by cyanobacteria and methanotrophs, respectively. However, wild strains produce generally low value carbon products like single cell protein or polyhydroxybutyrate. In order to produce higher value products, my work focuses on metabolic engineering of cyanobacteria and methanotrophs to channel and direct carbon flux.

Both CO₂ and methane are produced in concentrated streams from anaerobic digestion of municipal and agricultural wastewater, which creates a prime opportunity for co-utilization of gaseous carbon and nutrients in wastewater. Focusing on this opportunity, I worked to engineer cyanobacteria for improved phosphorus scavenging from wastewater. This bioremediation process removes an important contaminant while also producing a phosphate rich biofertilizer, with all of the carbon, energy, and nutrients supplied for free from waste. We conducted technoeconomic analysis to both estimate economic viability and to identify targets for engineering, highlighting important strain parameters to modify and process steps to simplify. In parallel work, I have engineered methanotrophs for producing medium chain fatty acids to offset scarce and unsustainable natural feedstocks. This process allows the capture and upgrading of methane produced and separated from anaerobic digestion, while making a sustainable oleochemical product providing higher value than native products or the methane feedstock.

Critically, these technologies can be applied to other sources of waste carbon gas, allowing for flexible production of sustainable chemicals. Future work can target ambient CO₂ and methane, other point sources like flue gas and remote oil wells, as well as new high value products like bioplastics and bioactive molecules.