Fermentative production of short-chain fatty acids in Escherichia coli

Abstract

Escherichia coli was engineered for the production of even-and odd-chain fatty acids (FAs) by fermentation. Co-production of thiolase, hydroxybutyryl-CoA dehydrogenase, crotonase and trans-enoyl-CoA reductase from a synthetic operon allowed the production of butyrate, hexanoate and octanoate. Elimination of native fermentation pathways by genetic deletion (DldhA, DadhE, DackA, Dpta, DfrdC) helped eliminate undesired by-products and increase product yields. Initial butyrate production rates were high (0.7 g l "1 h "1 ) but quickly levelled off and further study suggested this was due to product toxicity and/or acidification of the growth medium. Results also showed that endogenous thioesterases significantly influenced product formation. In particular, deletion of the yciA thioesterase gene substantially increased hexanoate production while decreasing the production of butyrate. E. coli was also engineered to co-produce enzymes for even-chain FA production (described above) together with a coenzyme B 12 -dependent pathway for the production of propionyl-CoA, which allowed the production of odd-chain FAs (pentanoate and heptanoate). The B 12 -dependent pathway used here has the potential to allow the production of odd-chain FAs from a single growth substrate (glucose) in a more energy-efficient manner than the prior methods.

Efficient odd straight medium chain free fatty acid production by metabolically engineered Escherichia coli

“…After further screening of TEs, the engineered strain, which was expressed TE Fs2108, produced 1,425 mg/L of valerate (McMahon and Prather, ). Volker et al () introduced propionyl‐ CoA synthesis pathway into engineered strain combined with the thiolase, hydroxybutyryl‐CoA dehydrogenase, crotonase, and trans‐enoyl‐CoA reductase. The resulting strain BE1952 accumulated 200 mg/L of valerate and 8 mg/L of enanthate under fermentative condition.…”

Fuelling the future: microbial engineering for the production of sustainable biofuels

“…Notably, CoA-dependent reverse β-oxidation also enables the production of odd-chain alcohols, as acetyl-CoA can be condensed with propionyl-CoA if a source of propionate is available 112 . Propionyl-CoA can be synthesized through ketobutyrate 113,114 , which is a metabolite downstream of the threonine biosynthesis pathway, or through the 1,2-propandiol pathway 115 . However, the production of odd-chain alcohols loses redox potential, which results in lower yields, unless properly balanced by pairing a redox-deficient pathway with a redox-surplus pathway 114 , whereas the production of even-chain alcohols from carbohydrates is redox balanced.…”

Fermentation of sweet sorghum derived sugars to butyric acid at high titer and productivity by a moderate thermophile Clostridium thermobutyricum at 50 °C

“…However, the reported titer of butyric acid in batch fermentations by these E. coli derivatives was ≤10 g.L -1 compared to Clostridium spp. (highest titer of about 45 g.L -1 in batch fermentations) (Vandak et al, 1995;Volker et al, 2014) with one study reporting as high as 62.5 g.L -1 using C. tyrobutyricum (Song et al, 2010). Although a mutant strain of C. acetobutylicum produced very low level of acetate and lactate as co-products during the butyrate production phase, the butyrate titer and yield of 32.5 g.L -1 and 0.39 g.g -1 (theoretical yield of butyrate from glucose is 0.49 g.g -1 ), respectively (Jang et al, 2014), are lower than the reported values for C. butyricum and C. tyrobutyricum listed above.…”