The cyclic monoterpene limonene is naturally found in the zests of lemons and is extensively used in fragrance, food and cosmetic industry. It also is gaining attention as jet fuel of biological origin. Genetically engineered Escherichia coli cells, also called cellular biocatalysts, produce limonene from the cheap and renewable resources glycerol and glucose by a fermentative process. This is achieved by the biotechnological introduction of enzymes into E. coli that are not a natural part of this bacterium but are able to catalyze the production of this compound.

Andreas Schmid and colleagues from TU Dortmund, Germany, investigated key parameters, such as pathway construction, gene expression, kinetics of the enzymes involved, physiology, reaction engineering and also the bioreactor setup, that influence the production of limonene of genetically modified E. coli. Their comprehensive approach shows that the optimization of such a whole cell process requires thorough analysis of all imaginable processes inside and outside of the microbial cell. By targeted engineering and strain selection they were able to achieve the highest monoterpene concentration ever obtained with a cellular biocatalyst to date.

• Engineering the productivity of recombinant Escherichia coli for limonene formation from glycerol in minimal media,
  Christian Willrodt, Christian David, Sjef Cornelissen, Bruno Bühler, Mattijs K. Julsing, Andreas Schmid,
  Biotechnol.J.2014.
  DOI: 10.1002/biot.201400023