Consolidated Bioprocessing: Synthetic Biology Routes to Fuels and Fine Chemicals

Abstract

The long road from emerging biotechnologies to commercial “green” biosynthetic routes for chemical production relies in part on efficient microbial use of sustainable and renewable waste biomass feedstocks. One solution is to apply the consolidated bioprocessing approach, whereby microorganisms convert lignocellulose waste into advanced fuels and other chemicals. As lignocellulose is a highly complex network of polymers, enzymatic degradation or “saccharification” requires a range of cellulolytic enzymes acting synergistically to release the abundant sugars contained within. Complications arise from the need for extracellular localisation of cellulolytic enzymes, whether they be free or cell-associated. This review highlights the current progress in the consolidated bioprocessing approach, whereby microbial chassis are engineered to grow on lignocellulose as sole carbon sources whilst generating commercially useful chemicals. Future perspectives in the emerging biofoundry approach with bacterial hosts are discussed, where solutions to existing bottlenecks could potentially be overcome though the application of high throughput and iterative Design-Build-Test-Learn methodologies. These rapid automated pathway building infrastructures could be adapted for addressing the challenges of increasing cellulolytic capabilities of microorganisms to commercially viable levels.

High-throughput genetic engineering of nonmodel and undomesticated bacteria via iterative site-specific genome integration

“…Engineered microbes promise to make substantial impacts on pressing societal challenges. Biotechnologies deployed in environments of biotic and abiotic complexity, such as cell-based therapeutics in the human gut ( 1 ), nitrogen fixation in the plant rhizosphere ( 2 , 3 ), and plastic ( 4 ) and plant biomass bioconversion ( 5 , 6 ) in industrial bioreactors ( 7 , 8 ), will be central in addressing grand challenges to promote human health, reverse carbon emissions, recycle mixed plastic waste, remediate contaminated soils, and achieve sustainable economies. Many natural microbes can thrive in these environments but lack the functions required to address these aims.…”

Metabolic engineering of Aspergillus niger to enhance production of ethanol

“…In essence, CBP consists of enzyme production, polysaccharide hydrolysis, and sugar fermentation. Many fungi are able to produce lignocellulolytic enzymes but not at the levels required by industry or they may not contain all of the key enzymes needed to degrade the plant biomass efficiently 11 . An interesting approach is to express ligninolytic enzymes in a single host.…”

“…Many fungi are able to produce lignocellulolytic enzymes but not at the levels required by industry or they may not contain all of the key enzymes needed to degrade the plant biomass efficiently. 11 An interesting approach is to express ligninolytic enzymes in a single host. Then there would be no need of using different fungi, and it may increase the ability to ferment lignocellulosic material in a single bioreactor, which may reduce the cost of biofuel production.…”

Deciphering Cellodextrin and Glucose Uptake in Clostridium thermocellum

“… Clostridium thermocellum (also named Ruminiclostridium thermocellum , Hungateiclostridium thermocellum , and Acetivibrio thermocellus ) is a thermophilic, lignocellulolytic, Gram-positive bacterium with great potential to be integrated into various strategies of lignocellulose biorefinery, particularly in consolidated bioprocessing and consolidated bio-saccharification ( 9 – 12 ). C. thermocellum produces a multienzyme complex, the cellulosome, which efficiently degrades cellulose into oligosaccharides ( 13 , 14 ).…”