(711c) Understanding the Stability and Robustness of a Methanotroph-Cyanobacterium Coculture through Kinetic Modeling and Experimental Verification

Understanding the Stability and
Robustness of a methanotroph-cyanobacterium coculture through kinetic modeling
and experimental verification

Kiumars
Badr, Matthew Hilliard, Q. Peter He and Jin Wang

Biogas
is comprised primarily of methane (50%~70%) and carbon dioxide (30% ~50%),
which can be produced from various waste sources, including landfill material,
animal manure; wastewater; and industrial, institutional, and commercial
organic wastes. 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].  It is clear that biogas
has immense potential as a renewable feedstock for producing high-density fuels
and commodity chemicals. 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.

However, development of multi-organism platforms for
commercial biogas conversion present significant challenges which center around
our ability to control function and composition of species in the coculture. An
essential tool for the optimization, design and analysis of the coculture based
biogas conversion is the development and validation of kinetics models that can
accurately describe and predict the co-culture growth under different
conditions. In this work, using Methylomicrobium buryatense - Arthrosipira platensis as the model coculture
system, we developed an unstructured model to capture the growth dynamics.
Specifically, Monod-like models were developed to capture coculture growth.
Substrate uptake consisted of both gas transferred from gas phase and that
produced in situ.  Figure 1 shows that the model with parameters
reported in literature show good agreement with our batch data.

Both batch
experiments using vials and continuous experiments using CSTR were conducted to
test the effects of different factors on the coculture growth, and the obtained
data were used for estimating model parameters. In this work we focus on the
light intensity and gas substrate compositions, as our preliminary results show
these are the two main factors that affect the stability and robustness of the
methanotroph-cyanobacterium coculture, while other factors can be easily
controlled during cell culture, such as pH, temperature. The obtained kinetic
model allows us to predict the stability region of the model coculture system,
and selected conditions are then validated experimentally.

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.; Badr, 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.