Whole‐cell biocatalysis: Advancements toward the biosynthesis of fuels

Abstract

The availability of robust microbial systems has facilitated the implementation of greener technology replacing existing less sustainable chemical technologies. Whole-cell biocatalysis has empowered the biological production of chemicals and biofuels, replacing labor-intensive traditional chemical catalysis. Whole-cell biocatalysis offers new avenues to use sustainable raw/waste biomass as a substrate for biotransformation into industrially important compounds. Using a native or nonnative microbial cell system as a chassis for developing a suitable cell catalyst requires multiple-level adjustments owing to the target product. Enzymes, the critical entity of biocatalysis, are an important factor influencing biocatalysis efficiency; whole cells provide optimal conditions to the enzymes or enzyme cascades for maximum productivity. Advancements in system biology and metabolic engineering techniques have led to the rational design of whole-cell catalysts for the suitable production of green fuels. Traditional enzyme catalysts are limited by issues such as enzyme stability and repeatability, laborious downstream processing and enzyme production technicalities, but whole-cell biocatalysis could bypass those bottlenecks. Thus, the application of whole cells in the catalysis and production of fuels has progressed greatly in the past couple of decades. This review focuses on detailing the concept of whole-cell biocatalysis and its advances in the production of biofuels such as alcohols and fatty acidbased, terpenoid-derived and carbon-free fuels. The technical advancements in various hosts such as Escherichia coli, Saccharomyces cerevisiae, Corynebacterium glutamicum and Synechococcus elongatus to establish whole-cell biocatalysis are summarized. In addition, system engineering toward the optimum production of various biofuels is added to the discussion.

Elucidating Electron Transfer Kinetics and Optimizing System Performance for Escherichia coli-Based Semi-Artificial H2 Production

“…Natural photosynthesis provides a good example of processes making use of solar energy to synthesize a number of valuable products, all while functioning under mild conditions and without the use of rare metals. 3 In the context of solar fuels and a future hydrogen society, enzymes capable of oxidizing or producing molecular hydrogen have gained a lot of interest. Among these enzymes, the so-called [FeFe] hydrogenases are of particular interest due to their high turn-over frequencies (TOFs) and energy efficiencies.…”

“…However, another possibility is the photosynthesis of solar fuels. Natural photosynthesis provides a good example of processes making use of solar energy to synthesize a number of valuable products, all while functioning under mild conditions and without the use of rare metals . In the context of solar fuels and a future hydrogen society, enzymes capable of oxidizing or producing molecular hydrogen have gained a lot of interest.…”

Biological Reaction Engineering for the Preparation of C9 Chemicals from Oleic Acid: 9-Aminononanoic Acid, 1,9-Nonanediol, 9-Amino-1-nonanol, and 1,9-Diaminononane

“…Afterward, the lipase from TLL was added into the culture broth to hydrolyze the ester bond of 9-(nonanoyloxy)nonanoic acid (4). This resulted in a formation of 9-HNA (6) and nnonanoic acid (5) to a rate of 20 mM/h (Panel II in Figure 2A). The final product concentration increased up to 12.2 mM, indicating a bioconversion of more than 95% from the ester product.…”

Continuous phase separation of stable emulsions from biphasic whole‐cell biocatalysis by catastrophic phase inversion

“…[5] In some cases also double or multiple emulsions can occur. [6,7] As much as emulsification is desired during the upstream processing (yielding in high surface areas and thus high mass transport rates), [1,3,8,9] downstream processing concepts often fail in processing the resulting (highly stable) Pickering-type emulsions. [10][11][12] Common concepts for the initial phase separation step of these emulsions, such as centrifugation, use of de-emulsifiers, filtration or membrane separations either fail, or require high effort in both costs and time.…”

“…As much as emulsification is desired during the upstream processing (yielding in high surface areas and thus high mass transport rates), [ 1,3,8,9 ] downstream processing concepts often fail in processing the resulting (highly stable) Pickering‐type emulsions. [ 10–12 ]…”