Bioconversion of crude glycerol to value-added compounds via recombinant microorganisms: A review

The valorization of side streams from industrial production is one of the key strategies to achieve more environmentally and economically sustainable manufacturing processes. Biodiesel biorefineries generate significant amounts of crude glycerol, which has potential for conversion into higher-value products. Instead of an expensive multistep purification procedure for the production of high-grade glycerol, there are many possible ways to utilize crude or partially purified glycerol directly by chemical or microbial conversions to produce valuable compounds. One approach is the use of enzymes, which often can be used directly in the biorefineries (e.g., lipases for transesterification). The use of microorganisms can be limited by the presence of impurities in crude glycerol, which may inhibit their growth and reduce product yields. While naturally robust strains are often required to withstand these conditions, recombinant DNA technology expands the utility of this substrate by engineering these microorganisms to produce specific, high-value compounds. This review provides a comprehensive overview of the microbial conversion of waste glycerol using recombinant and genetically modified strains, with particular emphasis on their potential for application in industry.