Abstract
Background3-hydroxypropionic acid (3-HP) is an important platform for the production of C3 chemicals, including acrylic acid, methyl acrylate, and acrylamide. Microbial production of 3-HP is mainly due to glycerol metabolism. In this study, in order to improve microbial 3-HP production, we applied a metabolic toggle switch for controlling the glycerol metabolism to redirect the excess metabolic flux of central metabolic pathway toward an exogenous 3-HP producing pathway in Escherichia coli.ResultsThe metabolic toggle switch enables conditional repression of the expression of a target gene during the fermentation. We individually performed conditional repression of glpK, tpiA, and gapA, which are involved in glycerol metabolism. The conditional repression of glpK and tpiA was not effective for 3-HP production under our experimental conditions. However, gapA conditional repression contributed to improve 3-HP production (titer, 54.2 ± 1.5 mM; yield, 32.1 ± 1.3 %) compared with that for the wild type strain. Additional deletion of endogenous yqhD, which is responsible for the production of a major byproduct, 1,3-propandiol, further increased 3-HP production (titer, 67.3 ± 2.1 mM; yield, 51.5 ± 3.2 %). The titer and yield were 80 and 94 % higher than those of the wild type strain, respectively. The obtained 3-HP yield from glycerol is comparable with the highest yield ever reported for microbial 3-HP production using glycerol as a sole carbon source. The measurement of intracellular metabolites showed the metabolic toggle switch successfully controlled the metabolic flux.ConclusionThe conditional repression of gapA by using the metabolic toggle switch combined with deletion of endogeneous yqhD increased 3-HP production approximately twofold from glycerol. This result indicates the metabolic toggle switch can be applied in various bio-production using diverse substrates.
Highlights
Growing concerns regarding the depletion of fossil resources and environmental sustainability have led to an increased demand for the development of bio-based chemicals and fuel production using renewable feedstock by microorganisms
Energy and cellular components were supplied from central carbon metabolism of glucose [33]. These results indicate that some amount of metabolic flux towards a central metabolic pathway such as glycolysis and the tricarboxylic acid (TCA) cycle is required during 3-hydroxypropionic acid (3-HP) production to supply energy and cellular components
TA2945 produced lactate, an intermediate of the methylglyoxal pathway. These results suggest that tpiA conditional repression led to the accumulation of dihydroxyacetone phosphate (DHAP), and that activation of the methylglyoxal pathway resulted in some amount of metabolic flux directed to the central metabolic pathway
Summary
Growing concerns regarding the depletion of fossil resources and environmental sustainability have led to an increased demand for the development of bio-based chemicals and fuel production using renewable feedstock by microorganisms. The conditional repression of gltA inhibited the metabolic flux from glycolysis to the TCA cycle and resulted in accumulation of acetyl-CoA This acetyl-CoA accumulation resulted in increased titer and yield of isopropanol (derived from acetyl-CoA) and avoided the severe growth defect observed using the conventional gene deletion [15]. This encouraged the use of MTS for other bio-production processes employing a synthetic pathway to improve productivity. There has been no report of controlling the metabolic flux using substrates other than glucose, such as xylose or glycerol
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
