(298h) Transforming Living Methanotrophs into Chemical Reactors

Reducing carbon emissions means addressing and utilizing carbon and energy from waste. Catalytic conversion of waste-derived, low-value carbon sources, e.g., CO₂ and CH₄, into high-value product streams under mild process conditions represents an economically viable route. Biocatalysts, such as live microorganisms, provide an attractive option for small-scale gas upgrading. The economic viability of biocatalytic approaches is evaluated by the volumetric product synthesis rates of the bioreactors, which is expected to be multiple grams of product per liter per hour. However, current aqueous stirred-tank bioreactors do not achieve high volumetric productivity in an energy efficient manner due largely to poor mass transfer from the gas to the liquid phase. To reach the required volumetric productivity a new bioreactor technology must be developed which increases mass transfer rates by 1-2 orders of magnitude relative to stirred vessels.

At LLNL, we have demonstrated efficient methane gas upgrading to methanol by printing enzyme-loaded polymeric materials. This is accomplished by advanced manufacturing techniques, which created unprecedented 3D gas-permeable microarchitectures that increase gas-to-liquid mass transfer by over an order of magnitude relative to current industrial methods.

To move beyond using expensive enzymes, we have developed new materials by entrapping live methanotroph cells in biocompatible, polymeric and 3D-printable materials, and demonstrated that the cells remained viable for a few days. We are using an engineered methanotroph strain (Methylococcus capsulatus) to convert methane gas into liquid organic acids, such lactic acid and muconic acid, both of which are of industrial interest. The first hurdle to entrapping whole cells in polymer is determining the material properties and biocompatibility. We will present the dissolved gas permeability of various formulations of porous silicone and polyethylene glycol, as well as the relationship between material thickness and gas transport. Additionally, we will show the biocompatibility of the materials by assessing the viability of entrapped methanotrophs. Finally, we will present data showing that the entrapped live methanotrophs are able to convert methane into the liquid organic acid products of interest.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. (LLNL-ABS-771899)