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.