New method could identify targets for bio-produced chemicals

A new modeling framework from UW-Madison could be used to identify economically viable candidates for bio-produced chemicals.

Tony Wenzhao Wu is the lead author of a study which details this identification method. He’s a PhD candidate from UW-Madison, and developed the method alongside Christos Maravelias, a professor of chemical engineering; and Jennifer Reed, an associate professor of chemical engineering.

He explains that these bio-produced chemicals are created through a process called microbial conversion.

“Biotechnologies today are quite advanced,” Wu says. “We can use metabolic engineering tools to genetically engineer microbes like E. coli and yeast to produce a lot of different chemicals that are currently produced from fossil fuel feed stocks like petroleum.”

He says researchers in his field have been hoping such bioproduction process would replace some of the traditional processes “for environmental benefits and also potentially economic advantages.”

For scientists like these, the fundamental question is how to target chemicals that show the most promise for biological production.

“This is the question we answer in this work,” Wu said.

According to him, studies in the past that have tried to get at this problem have focused on identifying platform chemicals that could be converted to final products later through chemical conversions.

“In other words, the focus was on studying a few interesting chemicals that currently attract a lot of attention, but we want to consider a much bigger pool of candidates,” he said, noting that many of those target chemicals can be made directly by microbes without needing to go through platform chemicals first.

In many past studies, Wu says discussions on economics have been “quite limited,” as the downstream separation cost was rarely considered.

“But the separation process that converts a very dilute product stream into high-purity final product is actually very expensive,” he said. “In many cases, that accounts for 60 to 80 percent of the total production cost — therefore, it needs to be considered.”  

The framework from Wu and his colleagues considers the separation cost, as well as other factors that play a role in economic viability.

At its core, this method involves starting with a wide range of database chemicals, then figuring out which ones can be produced through microbial conversion. Further screening criteria are then applied to identify the most promising chemicals.

In doing so, researchers look at many variables, including two important ones for the production process itself: yield, or how much product is produced per unit of sugar fed to the microbes; and residence time, which represents the speed of this reaction.

These two parameters are used to estimate the bioconversion cost for the chemical — just one of the three criteria. The other two are based on market data.

The second criterion enforces a minimum market volume or demand “because we do not want to build a tiny fermenter to serve a very small market,” Wu says.  

And the third is based on market size — price times the market volume. Wu says this must be large enough to meet revenue expectations, in order to recover capital investment.

Read the paper outlining the method here:

Watch a video with more explanation from Wu: