Production of biofuels and biochemicals by in vitro synthetic biosystems: Opportunities and challenges

Abstract

The largest obstacle to the cost-competitive production of low-value and high-impact biofuels and biochemicals (called biocommodities) is high production costs catalyzed by microbes due to their inherent weaknesses, such as low product yield, slow reaction rate, high separation cost, intolerance to toxic products, and so on. This predominant whole-cell platform suffers from a mismatch between the primary goal of living microbes - cell proliferation and the desired biomanufacturing goal - desired products (not cell mass most times). In vitro synthetic biosystems consist of numerous enzymes as building bricks, enzyme complexes as building modules, and/or (biomimetic) coenzymes, which are assembled into synthetic enzymatic pathways for implementing complicated bioreactions. They emerge as an alternative solution for accomplishing a desired biotransformation without concerns of cell proliferation, complicated cellular regulation, and side-product formation. In addition to the most important advantage - high product yield, in vitro synthetic biosystems feature several other biomanufacturing advantages, such as fast reaction rate, easy product separation, open process control, broad reaction condition, tolerance to toxic substrates or products, and so on. In this perspective review, the general design rules of in vitro synthetic pathways are presented with eight supporting examples: hydrogen, n-butanol, isobutanol, electricity, starch, lactate,1,3-propanediol, and poly-3-hydroxylbutyrate. Also, a detailed economic analysis for enzymatic hydrogen production from carbohydrates is presented to illustrate some advantages of this system and the remaining challenges. Great market potentials will motivate worldwide efforts from multiple disciplines (i.e., chemistry, biology and engineering) to address the remaining obstacles pertaining to cost and stability of enzymes and coenzymes, standardized building parts and modules, biomimetic coenzymes, biosystem optimization, and scale-up, soon.

An integrated approach: advances in the use ofClostridiumfor biofuel

“…The main advantages of such systems are -high product yield and freedom from complicated cellular regulation -but they also benefit from open process control, fast reaction rates, easy product separation, tolerance to toxic substrates or products and broad reaction conditions (Bornscheuer et al, 2012). Potential processes for the production of biofuels, including the clostridial production of isobutanol, through in vitro systems were reviewed by Zhang (2015).…”

Biotechnological and bioinformatics approaches for augmentation of biohydrogen production: A review

“…It aims at development of cell factories commonly microbial organisms, with the introduction of non-native pathways into optimized chassis strains for bioconversion of renewable resources to bulk or high value chemicals or alternatively for carbon capture to oppose climate change. In addition to the most important advantage-high product yield, in vitro synthetic biosystems highlight a few other biomanufacturing advantages, such as fast reaction rate, easy product separation, open process control, broad reaction condition, tolerance to toxic substrates or products [118]. The development of cell factories is mainly divided into three main phases: in silico design phase, the experimental phase and the phase of the quantitative evaluation of the novel strain [119].…”

Dark fermentation biorefinery in the present and future (bio)chemical industry

“…Enzymatic catalysis for synthesis of fine chemicals is already in used at industrial scale (Murzin and Leino 2008;Zhang 2014). Conventional enzymatic catalysis is carried out in organic solvents.…”