Abstract
BackgroundIn their quest for sustainable development and effective management of greenhouse gas emissions, our societies pursue a shift away from fossil-based resources towards renewable resources. With 95% of our current transportation energy being petroleum based, the application of alternative, carbon-neutral products—among them biodiesel—is inevitable. In order to enhance the cost structure of biodiesel biorefineries, the valorization of the crude glycerol waste stream into high-value platform chemicals is of major importance.ResultsThe purpose of this study is the production of 3-hydroxypropionaldehyde (3-HPA) from biodiesel-derived crude glycerol by Lactobacillus diolivorans. Particular focus is given on overcoming potential limitations of glycerol transport into the cell, in order to use the cells’ total glycerol dehydratase capability towards the formation of 3-HPA as the main product. Recombinant overexpression of the endogenous glycerol uptake facilitating protein PduF results in a significant increase of glycerol conversion by a factor of 1.3. Concomitantly, glycerol dehydratase activity increased from initially 1.70 ± 0.03 U/mg protein to 2.23 ± 0.11 U/mg protein. With this approach, an average productivity of 4.8 g3-HPA/(gCDM h) yielding up to 35.9 g/L 3-HPA and 0.91 mol3-HPA/molGlycerol have been obtained.ConclusionLactobacillus diolivorans proves to be a valuable cell factory for the utilization of crude glycerol delivering high-value C3 chemicals like 3-HPA, 1,3-propanediol (1,3-PDO) and 3-hydroxypropionic acid (3-HP). Enhancing the glycerol influx into the cell by genetic engineering was successful paving the way towards the commercial production of 3-HPA.
Highlights
In their quest for sustainable development and effective management of greenhouse gas emissions, our societies pursue a shift away from fossil-based resources towards renewable resources
Evaluation of major bottlenecks attributed to 3‐HPA formation in L. diolivorans The most crucial steps for the production of 3-HPA are the initial uptake of glycerol into the cell, followed by the conversion of the intracellular glycerol into 3-HPA by glycerol dehydratase
This study demonstrates for the first time the potential of L. diolivorans as a valuable cell factory for the valorization of crude glycerol towards 3-HPA extending the C3 product range from 1,3-PDO and 3-hydroxypropionic acid (3-HP) towards platform chemicals like acrolein and acrylic acid
Summary
In their quest for sustainable development and effective management of greenhouse gas emissions, our societies pursue a shift away from fossil-based resources towards renewable resources. Between 1970 and 2011, global greenhouse gas (GHG) emissions ( carbon dioxide) derived from fossil fuel combustion and industrial processes increased by 75% [1]. Key drivers for this dramatic increase in GHG can be related to alterations in population, structure of the economy, state of technology, and availability of fossil energy resources [2]. To counteract this trend, legal frameworks like the Paris Agreement aim at tackling global climate change, based on wide ranging changes. A concomitant production of fuels and chemicals in an integrated biorefinery, meets the environmental and economic goals simultaneously, due to high-value chemicals becoming the economic driver for the entire production plant [13, 14]
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