Abstract
Background3-Hydroxypropionic acid (3-HP) is one of the top value-added chemicals that can be produced from renewable resources. Crude glycerol, a cheap feedstock, is the foremost by-product generated from biodiesel industries. In this study, Klebsiella pneumonia was engineered for efficient 3-HP production from glycerol.ResultsThree metabolically engineered K. pneumoniae strains were constructed and the strain JJQ02 (ΔldhAΔdhaT) overexpressing aldehyde dehydrogenase from E. coli was the most suitable for 3-HP production. This strain produced 61.9 g/L of 3-HP (a yield of 0.58 mol/mol) in 38 h in a 5-L fermentor by control of the aeration rate. Deletion of ldhA and dhaT effectively eliminated lactate formation and reduced 1,3-propanediol production, but more 2,3-butanediol was accumulated due to redox balance. The fed-batch process was successfully scaled-up in a 300-L bioreactor where the 3-HP production level was 54.5 g/L (a yield of 0.43 mol/mol) in 51 h.ConclusionsDeficiency of both lactate dehydrogenase and 1,3-propanediol oxidoreductase as well as control of aeration significantly enhanced 3-HP production, and the successful scale-up of the fed-batch process in a 300-L bioreactor indicated a great potential to industrial production of 3-HP.
Highlights
The metabolites, including 3-Hydroxypropionic acid (3-HP), 1,3-propanediol, 2,3-butanediol, ethanol, succinic acid, lactic acid, acetic acid and formic acid were determined by a high performance liquid chromatography (HPLC) system (Shimazu, Kyoto, Japan) equipped with an organic acid analysis column (Aminex HPX-87H, 300 × 7.8 mm, Bio-Rad, USA), a refractive index detector (SPD-20A) and a UV/Vis detector (SPD-20AV)
Attempts have been made to reduce lactate production by deletion of the gene encoding lactate dehydrogenase (Kumar et al 2013b; Zhong et al 2014). Since both the reactions forming 1,3-propanediol and 3-HP compete for their common substrate 3-hydroxyaldehyde (3-HPA), deletion of propanediol oxidoreductase favors 3-HP production (Ashok et al 2011)
Lactate is a main inhibitor of 3-HP and 1,3-propanediol biosynthesis (Xu et al 2009b; Kumar et al 2013b)
Summary
Three metabolically engineered K. pneumoniae strains were constructed and the strain JJQ02 (ΔldhAΔdhaT) overexpressing aldehyde dehydrogenase from E. coli was the most suitable for 3-HP production. This strain produced 61.9 g/L of 3-HP (a yield of 0.58 mol/mol) in 38 h in a 5-L fermentor by control of the aeration rate. Deletion of ldhA and dhaT effectively eliminated lactate formation and reduced 1,3-propanediol production, but more 2,3-butanediol was accumulated due to redox balance. The fed-batch process was successfully scaled-up in a 300-L bioreactor where the 3-HP production level was 54.5 g/L (a yield of 0.43 mol/mol) in 51 h
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