Abstract
The potential that lies in harnessing the chemical synthesis capabilities inherent in living organisms is immense. Here we demonstrate how the biosynthetic machinery of Lactococcus lactis, can be diverted to make (3R)-acetoin and the derived 2,3-butanediol isomers meso-(2,3)-butanediol (m-BDO) and (2R,3R)-butanediol (R-BDO). Efficient production of (3R)-acetoin was accomplished using a strain where the competing lactate, acetate and ethanol forming pathways had been blocked. By introducing different alcohol dehydrogenases into this strain, either EcBDH from Enterobacter cloacae or SadB from Achromobacter xylosooxidans, it was possible to achieve high-yield production of m-BDO or R-BDO respectively. To achieve biosustainable production of these chemicals from dairy waste, we transformed the above strains with the lactose plasmid pLP712. This enabled efficient production of (3R)-acetoin, m-BDO and R-BDO from processed whey waste, with titers of 27, 51, and 32 g/L respectively. The corresponding yields obtained were 0.42, 0.47 and 0.40 g/g lactose, which is 82%, 89%, and 76% of maximum theoretical yield respectively. These results clearly demonstrate that L. lactis is an excellent choice as a cell factory for transforming lactose containing dairy waste into value added chemicals.
Highlights
The potential that lies in harnessing the chemical synthesis capabilities inherent in living organisms is immense
Acetoin has previously been shown to be toxic to bacteria[18] and so has 2,3-BDO, 2,3-BDO is less toxic than other alcohols[12,19]
A similar strategy has been used where NADH oxidase (NOX) from L. lactis was heterologously expressed in other bacteria to provide a redox sink and improve production of chemicals like pyruvate, acetoin and 2,3-BDO29–31
Summary
The potential that lies in harnessing the chemical synthesis capabilities inherent in living organisms is immense. To achieve biosustainable production of these chemicals from dairy waste, we transformed the above strains with the lactose plasmid pLP712 This enabled efficient production of (3R)-acetoin, m-BDO and R-BDO from processed whey waste, with titers of 27, 51, and 32 g/L respectively. The corresponding yields obtained were 0.42, 0.47 and 0.40 g/g lactose, which is 82%, 89%, and 76% of maximum theoretical yield respectively These results clearly demonstrate that L. lactis is an excellent choice as a cell factory for transforming lactose containing dairy waste into value added chemicals. The pure isomers sometimes have useful properties or specific applications, which make them very valuable, e.g. aqueous solutions of the stereoisomers of 2,3-butanediol have very low freezing points, as low as −65 °C, and they could be used as antifreeze agents[10] L. lactis has been engineered into producing a broad range of other useful compounds and shows great general potential as a cell factory for several reasons: It has a high glycolytic flux, is able to metabolize most of the common sugars, has a well-characterized metabolic network and is simple to manipulate genetically[15,16]
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