Microbial Propionic Acid Production

Abstract

Propionic acid (propionate) is a commercially valuable carboxylic acid produced through microbial fermentation. Propionic acid is mainly used in the food industry but has recently found applications in the cosmetic, plastics and pharmaceutical industries. Propionate can be produced via various metabolic pathways, which can be classified into three major groups: fermentative pathways, biosynthetic pathways, and amino acid catabolic pathways. The current review provides an in-depth description of the major metabolic routes for propionate production from an energy optimization perspective. Biological propionate production is limited by high downstream purification costs which can be addressed if the target yield, productivity and titre can be achieved. Genome shuffling combined with high throughput omics and metabolic engineering is providing new opportunities, and biological propionate production is likely to enter the market in the not so distant future. In order to realise the full potential of metabolic engineering and heterologous expression, however, a greater understanding of metabolic capabilities of the native producers, the fittest producers, is required.

Engineering Escherichia coli for propionic acid production through the Wood–Werkman cycle

“…Such is the case for propionibacteria , which are used for the production of propionic acid. Propionic acid is a C3 carboxylic acid used primarily in the food industry as an antimicrobial agent, and also can serve as a platform for the production of propanol and polypropylene (Gonzalez‐Garcia, McCubbin, Navone et al, ). While propionic acid is the main fermentation product of propionibacteria , these microorganisms have failed to deliver an economically viable biological production process for decades (Rodriguez, Stowers, Pham, & Cox, ; Stowers, Cox, & Rodriguez, ).…”

“…Relatively few genetic modification studies have been performed in propionibacteria (Gonzalez‐Garcia, McCubbin, Navone et al ; Guan et al, ; Liu et al, ) due to the limited availability of genetic modification tools. The alternative, random mutagenesis in propionibacteria , has successfully delivered economically viable strains (Luna‐Flores, Stowers, Cox, Nielsen, & Marcellin, ); however, quite often little learning results from random approaches (Jang et al, ).…”

High‐level heterologous production of propionate in engineered Escherichia coli

“…Using the double mutant CPC‐Sbm∆ sdhA ∆ iclR , we further demonstrated its excellent propionate‐producing capacity through fed‐batch cultivation under aerobic conditions of AL‐III (Figure 6) and AL‐IV (Figure 7), in particular, during certain feeding stages, such as Feeding 1 under AL‐III and AL‐IV, in which propionate biosynthesis was effective with high propionate yields of 60.2% and 73.1%, respectively, which are even comparable to those reached by natural producers (Gonzalez‐Garcia et al, 2017). It should be noted that propionate biosynthesis was active throughout the three feeding phases of both fed‐batch cultures.…”

“…Thus far, microbial production of propionate is conducted using natural producers of anaerobic Propionibaterium spp., such as Propionibacterium freudenreichii, Propionibacterium acidipropionici , and Propionibacterium shermanii . In spite of high propionate‐producing capacity, this genus can suffer various technological limitations, such as low growth rates, use of costly/complex growth media, lack of genetic amenability, and byproduct formation complicating downstream processing (Gonzalez‐Garcia et al, 2017). As a result, the use of genetically tractable bacterium Escherichia coli as a host for heterologous production of propionate has been proposed (Akawi, Srirangan, Liu, Moo‐Young, & Chou, 2015).…”

Acetogen Communities in the Gut of Herbivores and Their Potential Role in Syngas Fermentation

“…Propionate is generally regarded as a safe three-carbon chemical with varieties of applications, for example, it can be used as a food preservative or herbicide because of its antimicrobial properties [60] and can be used in the manufacture of cellulose derived plastics [61]. Other forms of propionate, such as propionate salts, can be used as perfume in the cosmetics industry, and citronellyl or geranyl propionate can be used as flavor enhancers in the food industry [62]. Through modifying the growth conditions or using a genetic engineering approach, some acetogen strains have been reported to produce other dominant products rather than acetate from syngas fermentation.…”