(175z) Efficient Biological Activation and Conversion of Short-Chain Hydrocarbons

Natural gas, consisting of methane and other short-chain hydrocarbons, is a significant contributor to greenhouse effect and global warming. After the breakthrough in extraction technology of oil and gas using horizontal drilling and hydraulic fracturing, the opportunities for utilization of natural gas have dramatically increased. These gaseous short-chain hydrocarbons are difficult to transport and store and their high C-H bond energy makes their conversion to value-added products very challenging. Existing technologies such as catalytic conversion and steam cracking require large-scale facilities to be profitable due to high energy input for the activation of C-H bonds. These traditional chemical plants are not ideal for current shale gas utilization due to high CapEx and large environmental footprints. As a result, in many sources including gas reserves and landfills, methane is either flared or released to the atmosphere.

While short-chain hydrocarbons are among the least reactive organic compounds, diverse microorganisms are capable of consuming alkanes for biomass and energy production. The corresponding metabolic pathways are generally efficient and hence the use of biobased conversion systems are highly sought. We are characterizing and engineering these metabolic pathways and assessing their performance in in vitro and in vivo settings to convert short-chain alkanes to target products such as alcohols. An important target is the oxygen-independent activation of alkane substrates by enzymes called alkylsuccinate synthases, and metabolic conversion of resulting metabolites into higher-value products. In addition to expressing and characterizing enzyme-activase pairs, we aim to reconstitute metabolic pathways in E. coli whereby methyl-alkyl-succinates generated from alkane activation are processed into acyl-CoA intermediates and ultimately end-product alcohols. Establishing the complete alkylsuccinate metabolic cycle involves identification and/or engineering of enzymes having novel substrate specificities. Suitable final electron acceptors that support sufficient respiration (ATP generation and thermodynamic favorability) are being identified in conjunction with pathway assembly. The overall strategy combines protein and metabolic engineering to establish a novel strain engineering platform for biocatalytic processes with enhanced carbon and energy efficiencies.