Cell-free Biosystems in the Production of Electricity and Bioenergy

Abstract

: Increasing needs of green energy and concerns of climate change are motivating intensive R&D efforts toward the low-cost production of electricity and bioenergy, such as hydrogen, alcohols, and jet fuel, from renewable sugars. Cell-free biosystems for biomanufacturing (CFB2) have been suggested as an emerging platform to replace mainstream microbial fermentation for the cost-effective production of some biocommodities. As compared to whole-cell factories, cell-free biosystems comprised of synthetic enzymatic pathways have numerous advantages, such as high product yield, fast reaction rate, broad reaction condition, easy process control and regulation, tolerance of toxic compound/product, and an unmatched capability of performing unnatural reactions. However, issues pertaining to high costs and low stabilities of enzymes and cofactors as well as compromised optimal conditions for different source enzymes need to be solved before cell-free biosystems are scaled up for biomanufacturing. Here, we review the current status of cell-free technology, update recent advances, and focus on its applications in the production of electricity and bioenergy.

A cost-effective polyphosphate-based metabolism fuels an all E. coli cell-free expression system

“…Moreover, the efficiency of the system presented herein, could be further improved by replacing expensive nucleoside triphosphates (NTPs) with nucleoside monophosphate (NMPs) and exploit the endogenous enzymes to regenerate NTPs (Calhoun and Swartz, 2005;Jewett et al, 2008) The novel ATP-regeneration system presented in this work is suitable for semi-and continuous systems for in vitro protein synthesis (Spirin and Swartz, 2008), industrial applications (Swartz, 2006), high-throughput experiments (Caschera et al, 2011) and large-scale reaction using cell-free or enzyme technology (Butler, 1977). Our study also demonstrates that cell-free transcription-translation systems are valuable platforms for understanding and developing novel metabolic pathways (Zhang et al, 2007;Zhu et al, 2013).…”

“…We demonstrate that hexametaphosphate (HMP), a polyphosphate molecule (NaPO 3 ) 17 , is efficiently used to fuel protein synthesis when coupled to a carbon source such as maltose or maltodextrin. In addition to reduce the cost of the ATP-regenerating system, we develop new knowledge of in vitro metabolic pathways and provide an alternative system to a rapidly growing research area (Carlson et al, 2012;Zhu et al, 2013).…”

Exploring the Feasibility of Cell-Free Synthesis as a Platform for Polyhydroxyalkanoate (PHA) Production: Opportunities and Challenges

“…Artificial analogs can substitute for expensive cofactors [ 118 ] and can be designed to be more stable than their natural counterparts while still being recognized by enzymes. The CoA cycle is crucial for PHA synthesis, but its dependence on chemicals for cofactor repair in vitro hinders CoA from being stable for extended periods [ 119 ]. More comprehensive reviews of cofactor and ATP regeneration systems have been reported [ 110 , 120 , 121 ].…”

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

“…Although each of these challenges can be addressed from multiple aspects, some potential solutions are too complex to implement and may also be detrimental factors in terms of other aspects of cell performance. Due to the complexity of these challenges, a systematic analysis should be made to identify the key reasons behind each challenge and to then carefully evaluate multiple possible solutions …”