Isobutene (2-methylpropene) is one of those chemicals for which bio-based production might replace the petrochemical production in the future. Currently, more than 10 million metric tons of
isobutene are produced on a yearly basis. Even though bio-based production might also be achieved through chemocatalytic or thermochemical methods, this review focuses on fermentative routes from
sugars. Although
biological isobutene formation is known since the 1970s, extensive metabolic engineering is required to achieve economically viable yields and productivities. Two recent metabolic engineering developments may enable anaerobic production close to the theoretical stoichiometry of 1isobutene + 2CO(2) + 2H(2)O per mol of
glucose. One relies on the conversion of 3-hydroxyisovalerate to
isobutene as a side activity of
mevalonate diphosphate decarboxylase and the other on
isobutanol dehydration as a side activity of engineered
oleate hydratase. The latter resembles the fermentative production of
isobutanol followed by
isobutanol recovery and chemocatalytic
dehydration. The advantage of a completely
biological route is that not
isobutanol, but instead gaseous
isobutene is recovered from the fermenter together with CO(2). The low aqueous solubility of
isobutene might also minimize product toxicity to the microorganisms. Although developments are at their infancy, the potential of a large scale fermentative
isobutene production process is assessed. The production costs estimate is 0.9 Euro kg(-1), which is reasonably competitive. About 70% of the production costs will be due to the costs of
lignocellulose hydrolysate, which seems to be a preferred feedstock.