Microbial Conversion of Glycerol to Value-Added Chemicals

Glycerol, generated in large surplus as a by-product of biodiesel manufacture, presents a low-cost and highly reduced feedstock for biotechnological processes. Microorganisms can channel glycerol into a diverse portfolio of chemicals including polyols such as 1,3-propanediol, organic acids such as succinate and dihydroxyacetone, solvents such as ethanol and butanol, and bulk and speciality chemicals such as diols and biofuels. Two principal metabolic routes underpin conversion: oxidative pathways that yield dihydroxyacetone and organic acids, and reductive pathways that generate 1,3-propanediol and other reduced compounds. Wild-type strains such as Klebsiella, Clostridium and Lactobacillus species have evolved glycerol dehydratase and glycerol dehydrogenase activities that catalyse key steps, but yields and productivities are often limited by by-product formation, redox imbalance and the presence of inhibitory impurities in crude glycerol. Metabolic engineering and process intensification strategies—ranging from pathway redirection and enzyme overexpression to fed-batch and continuous cultivation—have substantially increased titres and rates. Mixed cultures and microbial consortia have also been explored to exploit functional redundancies, improve tolerance to osmotic stress and enable co-utilisation of lignocellulosic hydrolysates. These advances contribute to the economic viability of glycerol biorefineries and support the transition to more sustainable chemical production.

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Microbial Conversion of Glycerol to Value-Added Chemicals publication trend

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Technical terms

Glycerol dehydratase: A vitamin B₁₂-dependent enzyme that converts glycerol to 3-hydroxypropionaldehyde.

1,3-Propanediol dehydrogenase: An oxidoreductase that reduces 3-hydroxypropionaldehyde to 1,3-propanediol using NADH.

Metabolic engineering: The redirection and optimisation of cellular pathways by genetic modifications to improve production of desired metabolites.

Fed-batch fermentation: A cultivation mode in which substrates are incrementally added to a bioreactor to control growth rate and prolong production phases.

References

1. Key enzymes catalyzing glycerol to 1,3-propanediol. Biotechnology for Biofuels and Bioproducts (2016).
2. Impurities of crude glycerol and their effect on metabolite production. Annals of Microbiology (2013).
3. Toward glycerol biorefinery: metabolic engineering for the production of biofuels and chemicals from glycerol. Biotechnology for Biofuels and Bioproducts (2016).
4. Consistent 1,3-propanediol production from glycerol in mixed culture fermentation over a wide range of pH. Biotechnology for Biofuels and Bioproducts (2016).
5. High-yield production of 1,3-propanediol from glycerol by metabolically engineered Klebsiella pneumoniae. Biotechnology for Biofuels and Bioproducts (2018).
6. Enhancement of 1,3-propanediol production from industrial by-product by Lactobacillus reuteri CH53. Microbial Cell Factories (2020).
7. Advances in industrial microbiome based on microbial consortium for biorefinery. Bioresources and Bioprocessing (2017).