(69a) Invited Talk: Designing High-Capacity Microbial and Enzymatic Bioreactors

Two types of bioreactors are typically seen in industrial biotechnology, microbial bioreactor (or fermentor) and enzymatic bioreactor, which use microbial cells and enzymes respectively as the biocatalyst for biomanufacturing. Microbial bioreactors are designed to provide carbon source (typically sugars derived from renewable biomass) and nutrients (nitrogen, oxygen, micronutrients) and a growth environment to grow cells (bacteria or yeast) to a desired density. The cells in the bioreactor then convert additional carbon source into the desired products with added values. As cells are the biocatalyst, high-density cell culture is desired to achieve high titer, rate, and yield (TRY) of the fermentation product of interest. However, restrictions in physical designs (reactor size, oxygen transfer rate, heat transfer efficiency, operation modes), biological cell performance (genetic instability, tolerance of inhibitors and high concentrations of substrate and product), and capital investment may significantly limit the capacity of the microbial bioreactors at industrial scale. For enzymatic bioreactors, enzymes produced from microbial cell cultures are recovered and used as the catalyst to convert specific substrates into new products of industrial interests. The cost, stability, and efficiency of an enzyme are critical to an enzymatic reaction. The robustness of the reaction at high-levels of substrate loading and high concentrations of produced products also limit the production capacity of an enzymatic bioreactor at industrial scale due to the challenges in mixing and mass transfer.

In this talk, I will share the research studies on three different projects in my group to address the challenges for high-capacity bioreactors. In the first project, we designed a bioreactor system that can use engineered oleaginous yeast Yarrowia lipolytica for producing high-value products such as wax ester and omega-3 fatty acids from waste cooking oils (WCOs), which are hydrophobic and cause limitations in mixing and mass transfer. The computational fluid dynamics (CFD) study was found critical in helping understand the mixing challenges and design the new bioreactors. In the second project, we developed a continuous fermentation process for the Yarrowia lipolytica yeast fermentation, which was able to grow cells up to 150 g/L DCW to make product(s) at much higher productivities. The continuous process was designed with the assistance of dynamic modeling and validated by experiments for more than seven weeks. In the third project, we designed an enzymatic reaction system that can use an engineered PET hydrolase, LCC (leaf-branch compost cutinase), to decompose post-consumer poly(ethylene) terephthalic acid (PET) plastic. The LCC enzyme was produced by E. coli cells for 1.2 g/L, and then purified and used for the reaction containing up to 300 g/L post-consumer PET. Complete PET degradation was achieved within 2 days with the limited use of the enzyme. Economics for the enzymatic reaction will also be briefly discussed.