(360a) Screening for Promising Microorganism-Produced Bio-Chemicals

Screening for Promising Microorganism-Produced
Bio-Chemicals

Wenzhao Wu, Matthew Long, Jennifer
Reed, Christos T. Maravelias^*

Dept.
of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI 53706

The last decade has seen tremendous progress in
metabolic engineering and synthetic biology^1,2. These advancements enable
the use of engineered microorganisms such as Escherichia coli, yeast and algae for the production of chemicals
that are currently derived mainly from fossil fuel feedstocks^3,4.
However, which chemicals have the highest economic potential remains unclear.
Toward this end, we develop a framework for the identification of promising
chemicals for bio-based production. 

We first examine the US high-production-volume
(HPV) chemicals⁵, which are manufactured in or imported into the
United States in amounts equal to or greater than 454 metric tonnes (MT) per
year. HPV chemicals include all commodity chemicals and a portion of fine
chemicals. We establish an HPV chemical database (3574 chemicals) by compiling
several HPV lists published by the EPA over the past two decades. Then we
intersect the HPV chemical database with the KEGG database, which includes most
of chemicals produced by characterized reactions in biological systems, and thus
613 overlapping chemicals are found. These chemicals are then imported into a genome-scale
metabolic model, and 168 chemicals are identified to be producible by microorganisms,
often with the addition of heterologous reactions. These 168 chemicals are the
complete pool of candidate targets for bio-based production. In addition,
market volume and price data is collected for each of them.

Next, we develop three screening criteria to quantify
economic potential.

Criterion 1: “separation cost margin”. The largest the
difference between a chemical’s selling price and its production cost is, the largest
its economic potential is. However, the downstream separation cost is highly
product-dependent and difficult to estimate. Therefore, we quantify the economic
potential using the “separation cost margin”, which is the difference between
the price and the upstream cost (including raw material supply cost and
bio-conversion cost). We calculate the upstream cost using base cost data from the
literature, and theoretical productivity and titer calculated using our
metabolic model.

Criterion 2: market volume. The market volume
should be greater than an expected production capacity. The specific capacity
is estimated based on the type of the bio-conversion system. For example, the
capacity for an open pond system can be estimated based on the area of a
typical open pond facility.

Criterion 3: market value. The market value
should be large enough to attract investment and recover capital cost within an
expected time horizon.

Note that the specific values adopted in these
criteria depend on the type of supply sources (e.g. flue gas, CO₂, or
sugar as the carbon source), bio-conversion type (photosynthesis or
fermentation-based), specific reactor types (continuous or batch), and
classification of chemicals (commodity or fine chemical). We investigate several
benchmark scenarios. For example, we apply the three criteria on all the
commodity chemicals in the candidate pool, assuming photosynthetic bio-conversion
in a batch reactor.

Finally, we present detailed results for a specific
system: cultivation of photosynthetic bacteria in a continuously operating open
pond system, supplied with captured CO₂ from flue gas, and nutrients
and water from a waste water treatment facility. We set a uniform separation
cost margin for all chemicals to be greater than 1.8 $/kg, which is an
estimated margin for a benchmark product - polyhydroxyalkanoate (PHA). The volume
was set to be greater than 31751 MT/year, calculated from an expected open pond
area of at least 1000 ha. Finally, the market size was assumed to be greater
than 200 million $/year to be attractive enough for investment, and to recover
capital cost in ~5 years supposing a 50% market share. Applying all the three
criteria on the 168 chemical candidates, as a preliminary result, we identify
four chemicals as the most promising ones: glutaric acid, acrylamide, propanal,
and octanoic acid.

References

[1] Gavrilescu, M. & Chisti, Y., 2005. Biotechnology- a sustainable
alternative for chemical industry. Biotechnology advances, Volume 23,
pp. 471-499.

[2] Bornscheuer, U. T. & Nielsen, A. T., 2015. Editorial overview:
chemical biotechnology: interdisciplinary concepts for modern biotechnological
production of biochemicals and biofuels. Current Opinion in Biotechnology, Volume
35, pp. 133-134.

[3] Wilson, S. A. & Roberts, S. C., 2014. Metabolic engineering
approaches for production of biochemicals in food and medicinal plants. Current
Opinion in Biotechnology, Volume 26, pp. 174-182.

[4]
Zhang, X., Tervo, C. J. & Reed, J. L., 2016. Metabolic Assessment of E.
coli as a Biofactory for Commercial Products. Metabolic Engineering, Volume
35, pp. 64-74.

[5]
US EPA, 2004. High-production-volume (HPV) chemicals status and future
directions of the HPV Challenge Program. Office
of Pollution Prevention and Toxics, Washington DC.