Strategies for efficient and economical 2,3-butanediol production: new trends in this field.

2,3-Butanediol (2,3-BD) is a promising bulk chemical with a potentially wide range of applications e.g., in the manufacture of printing inks, perfumes, synthetic rubber, fumigants, antifreeze agents, fuel additives, foodstuffs and pharmaceuticals. Its high heating value and ability to increase the octane number of fuels make 2,3-BD a promising drop-in fuel. It can also be converted to methyl-ethyl ketone (MEK), which is considered an effective liquid fuel additive. After combination with MEK and hydrogenation reaction, 2,3-BD can be converted to octane, which is used to produce high-quality aviation fuel. Currently 2,3-BD is mainly produced on an industrial scale by chemical methods. However, microbiological production of 2,3-BD offers a less expensive and more environmentally friendly alternative to traditional synthesis. This alcohol is generated from hexoses and pentoses mainly by bacterial strains of the genera Klebsiella, Bacillus, Serratia, and Enterobacter, which can convert waste products (such as glycerol and agricultural residues) and excess biomass (such as wood hydrolysates) to 2,3-BD. Recently, a significant improvement in microbial production has been achieved by the screening of efficient natural microbial strains, the application of alternative cost-effective substrates, and the genetic improvement of microbial producers. Furthermore, Klebsiella strains, which are regarded the most efficient natural 2,3-BD producers, have been subjected to genetic modifications aiming at the removal of pathogenic factors and the development of avirulent strains that could be used for the safe production of the diol. This review summarizes existing knowledge and experience concerning various strategies for efficient and economical microbial production of 2,3-BD.