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Research Publications (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/213

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Subject: search.filters.subject.d-Lactate production

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    Improvement of d-lactate productivity in recombinant Escherichia coli by coupling production with growth
    (Springer Netherlands, 2012-06) Zhou, Li; Tian, Kang-Ming; Niu, Dan-Dan; Shen, Wei; Shi, Fui-Yang; Singh, Suren; Wang, Zheng-Xiang
    Coupling lactate fermentation with cell growth was investigated in shake-flask and bioreactor cultivation systems by increasing aeration to improve lactate productivity in Escherichia coli CICIM B0013-070 (ackA pta pps pflB dld poxB adhE frdA). In shake-flasks, cells reached 1 g dry wt/l then, cultivated at 100 rpm and 42°C, achieved a twofold higher productivity of lactic acid compared to aerobic and O2-limited two-phase fermentation. The cells in the bioreactor yielded an overall volumetric productivity of 5.5 g/l h and a yield of 86 g lactic acid/100 g glucose which were 66% higher and the same level compared to that of the aerobic and O2-limited two-phase fermentation, respectively, using scaled-up conditions optimized from shake-flask experiments. These results have revealed an approach for improving production of fermentative products in E. coli.
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    Genetically switched D-lactate production in Escherichia coli
    (Elsevier, 2012-06-08) Singh, Suren
    During a fermentation process, the formation of the desired product during the cell growth phase competes with the biomass for substrates or inhibits cell growth directly, which results in a decrease in production efficiency. A genetic switch is required to precisely separate growth from production and to simplify the fermentation process. The ldhA promoter, which encodes the fermentative d-lactate dehydrogenase (LDH) in the lactate producer Escherichia coli CICIM B0013-070 (ack-pta pps pflB dld poxB adhE frdA), was replaced with the λ pR and pL promoters (as a genetic switch) using genomic recombination and the thermo-controllable strain B0013–070B (B0013-070, ldhAp::kan-cIts857-pR–pL), which could produce two-fold higher LDH activity at 42 °C than the B0013-070 strain, was created. When the genetic switch was turned off at 33 °C, strain B0013-070B produced 10% more biomass aerobically than strain B0013-070 and produced only trace levels of lactate which could reduce the growth inhibition caused by oxygen insufficiency in large scale fermentation. However, 42 °C is the most efficient temperature for switching on lactate production. The volumetric productivity of B0013-070B improved by 9% compared to that of strain B0013-070 when it was grown aerobically at 33 °C with a short thermo-induction at 42 °C and then switched to the production phase at 42 °C. In a bioreactor experiment using scaled-up conditions that were optimized in a shake flask experiment, strain B0013-070B produced 122.8 g/l d-lactate with an increased oxygen-limited productivity of 0.89 g/g·h. The results revealed the effectiveness of using a genetic switch to regulate cell growth and the production of a metabolic compound.