(20d) 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.