Production of succinic acid from sucrose and sugarcane molasses by metabolically engineered Escherichia coli

Metabolic engineering of industrial platform microorganisms for biorefinery applications--optimization of substrate spectrum and process robustness by rational and evolutive strategies

Bio-based production promises a sustainable route to myriads of chemicals, materials and fuels. With regard to eco-efficiency, its future success strongly depends on a next level of bio-processes using raw materials beyond glucose. Such renewables, i.e., polymers, complex substrate mixtures and diluted waste streams, often cannot be metabolized naturally by the producing organisms. This particularly holds for well-known microorganisms from the traditional sugar-based biotechnology, including Escherichia coli, Corynebacterium glutamicum and Saccharomyces cerevisiae which have been engineered successfully to produce a broad range of products from glucose. In order to make full use of their production potential within the bio-refinery value chain, they have to be adapted to various feed-stocks of interest. This review focuses on the strategies to be applied for this purpose which combine rational and evolutive approaches. Hereby, the three industrial platform microorganisms, E. coli, C. glutamicum and S. cerevisiae are highlighted due to their particular importance.

Construction of homologous and heterologous synthetic sucrose utilizing modules and their application for carotenoid production in recombinant Escherichia coli

Sucrose is one of the most promising carbon sources for industrial fermentation. We expressed synthetic modules expressing genes of the PEP-PTS and non-PTS pathways in Escherichia coli K12 for comparison. We selected PEP-PTS pathway genes of Lactobacillus plantarum and Staphylococcus xylosus and non-PTS pathway genes of sucrose-utilizing (Scr(+)) E. coli EC3132. Switchable Scr(+) modules expressing E. coli EC3132 non-PTS genes conferred better sucrose-utilizing ability on Scr(-)E. coli K12 than E. coli EC3132. Scr(+) modules expressing S. xylosus PEP-PTS genes conferred a sucrose-utilizing ability on E. coli K12. Among L. plantarum PEP-PTS genes, SacA(LP) and SacK(LP) were functional in E. coli K12. CscA(EC)-CscB(EC)-CscK(EC) (non-PEP-PTS module) or ScrA(SX)-SacA(LP)-SacK(LP) (PEP-PTS module) was introduced to a diapolycopene-producing E. coli strain. In both Scr(+)E. coli K12, the sucrose-utilizing ability of the modules was not affected by diapolycopene formation, indicating that the modular Scr(+) systems could be employed for developing sustainable bioprocesses using sucrose.

Metabolic engineering of Klebsiella oxytoca M5a1 to produce optically pure D-lactate in mineral salts medium

Klebsiella oxytoca strains were constructed to produce optical pure d-lactate by pH-controlled batch fermentation in mineral salts medium. The alcohol dehydrogenase gene, adhE, and the phospho-transacetylase/acetate kinase A genes, pta-ackA, were deleted from the wild type. KMS002 (ΔadhE) and KMS004 (ΔadhE Δpta-ackA) exhibited d-lactate production as a primary pathway for the regeneration of NAD(+). Both strains produced 11-13 g/L of d-lactate in medium containing 2% (w/v) glucose with yields of 0.64-0.71 g/g glucose used. In sugarcane molasses, KMS002 and KMS004 produced 22-24 g/L of d-lactate with yields of 0.80-0.87 g/g total sugars utilized. Both strains also utilized maltodextrin derived from cassava starch and produced d-lactate at a concentration of 33-34 g/L with yields of 0.91-0.92 g/g maltodextrin utilized. These d-lactate yields are higher than those reported for engineered E. coli strains.

Comparative reaction engineering studies for succinic acid production from sucrose by metabolically engineered Escherichia coli in fed-batch-operated stirred tank bioreactors

This study presents a comparative reaction engineering analysis of metabolically engineered sucrose-utilizing Escherichia coli derived from E. coli K12 MG1655 for the anaerobic production of succinic acid. Production capacities of 16 different recombinant strains were evaluated in 48 parallel fed-batch-operated milliliter-scale stirred tank bioreactors (10 mL) with continuous CO₂ sparging. The effects of recombinant sucrose-utilization systems (csc-operon or scr-operon), enhancements of anaplerotic reactions (pck, ppc, maeA, maeB or heterologous pyc) and gene deletions (ldhA, adhE, ack-pta and ptsG) were studied with respect to the overall process performances of the respective recombinant strains. Both sucrose-utilization systems enabled the production of succinic acid from sucrose in E. coli K12 MG1655. Maximum succinate production was observed by overexpressing the pyruvate carboxylase from Corynebacterium glutamicum resulting in a succinate concentration of 26.8 g L⁻¹ after 48 h and a cell-specific productivity of 0.14 g g⁻¹ h⁻¹. Further experiments in a fed-batch-operated laboratory-scale stirred tank bioreactor (2 L) showed that micro-aerobic conditions preceding the anaerobic phase enhance succinic acid production of E. coli K12 MG1655-derived strains. The work demonstrates the importance of parallel approaches within the scope of applied metabolic engineering studies.

Economical production of poly(γ-glutamic acid) using untreated cane molasses and monosodium glutamate waste liquor by Bacillus subtilis NX-2

The production of poly(γ-glutamic acid) by Bacillus subtilis NX-2 from cane molasses and monosodium glutamate waste liquor (MGWL) was studied for the first time in this work. When batch fermentation was carried out with untreated molasses, 33.6±0.37 g L(-1) PGA was obtained with a productivity of 0.46±0.006 g L(-1) h(-1). In order to minimize the substrate inhibition, fed-batch fermentation was performed with untreated or hydrolyzed molasses in 7.5 L bioreactor, giving 50.2±0.53 and 51.1±0.51 g L(-1) of PGA at 96 h, respectively. Further studies were carried out by using MGWL as another carbon source, resulting in a PGA concentration of 52.1±0.52 g L(-1) with a productivity of 0.54±0.003 g L(-1) h(-1). These results suggest that the low-cost cane molasses and MGWL can be used for the environmental-friendly and economical production of PGA by B. subtilis NX-2.