Photoautotroph-Methanotroph Coculture – a Flexible Platform for Efficient Biological CO2-CH4 Co-Utilization

Photoautotroph-Methanotroph Coculture – A Flexible Platform for Efficient Biological CO₂-CH₄ Co-utilization

Kiumars Badr*, Matthew Hilliard*, Q. Peter He*, Jin Wang*⁺

*Department of Chemical Engineering, Auburn University, Auburn, AL 36849 USA
 (KB: kzb0054@auburn.edu; MH: mvh0006@auburn.edu; QPH: qhe@auburn.edu; ⁺JW: wang@auburn.edu)

 

Industrial, municipal, and agricultural waste streams containing stranded organic carbon, which can be converted into biogas through anaerobic digestion. Biogas is comprised primarily of methane (50%~70%) and carbon dioxide (30% ~50%), which are potent global warming gases, while methane is also a valuable fuel. It has been demonstrated that biogas has immense potential as a renewable feedstock for producing high-density fuels and commodity chemicals. Specifically, EPA estimates that currently US biogas production potential is 654 billion cubic feet per year, which could displace 7.5 billion gallon of gasoline [1].  However, the utilization of biogas represents a significant challenge due to its low pressure and presence of contaminants such as H₂S, ammonia, and volatile organic carbon compounds. To tap into this immense potential, effective biotechnologies that can co-utilize both CO₂ and CH₄ are needed.

In our previous work, we have demonstrated that metabolic coupling of methane oxidation to oxygenic photosynthesis can be a highly efficient way to recover the energy and capture carbon from biogas. Using the principles that drive the natural consortia [2,3,4], we have assembled several synthetic methanotroph-photoautotroph cocultures that exhibit stable growth under various substrate delivery and illumination regimes [5]. From an engineering perspective, coupling methanotrophic metabolism to photosynthesis offers three major advantages for biological biogas conversion. First, exchange of in situ produced O₂ and CO₂ dramatically reduces mass transfer resistance of the two gas substrates, which can dramatically increases the growth of both strains; Second, in situ O₂ consumption removes inhibition on photoautotroph and eliminates risk of explosion; Third, interdependent yet compartmentalized configuration of the coculture offers flexibility and more options for metabolic engineering.

In this work, we present the very first effort to quantitatively model the growth dynamics of a photoautotroph-methanotroph coculture, as well as the experimental and computational tools that are required to characterize the coculture. Together, these progress help enable us to further examine the potential interactions within the coculture.

Reference:

[1] Chris Voell (2016), Trends & Resources for U.S. Biogas Projects in the Livestock Sector, German American Bioenergy Conference, Atlanta, GA, Nov. 2016;

[2] Kip, N.; van Winden, J. F.; Pan, Y.; Bodrossy, L.; Reichart, G.-J.; Smolders, A. J.; Jetten, M. S.; Damsté, J. S. S.; den Camp, H. J. O. Global Prevalence of Methane Oxidation by Symbiotic Bacteria in Peat-Moss Ecosystems. Nat. Geosci. 2010, 3, 617.

[3] Raghoebarsing, A. A.; Smolders, A. J.; Schmid, M. C.; Rijpstra, W. I. C.; Wolters-Arts, M.; Derksen, J.; Jetten, M. S.; Schouten, S.; Damsté, J. S. S.; Lamers, L. P. Methanotrophic Symbionts Provide Carbon for Photosynthesis in Peat Bogs. Nature 2005, 436, 1153.

[4] Milucka, J.; Kirf, M.; Lu, L.; Krupke, A.; Lam, P.; Littmann, S.; Kuypers, M. M.; Schubert, C. J. Methane Oxidation Coupled to Oxygenic Photosynthesis in Anoxic Waters. ISME J. 2015.

[5] Roberts, N.; Hilliard, M.; Bahr, K.; He, Q. P.; Wang, J. Coculture of Methanotrophs and Microalgae – a Flexible Platform for Biological CH4\/CO2 Co-Utilization, 2017 AIChE Annual Conference, Oct. 28 – Nov. 3, 2017, Minneapolis, MN. This work won 2017 AIChE Session’s Best Paper Award.