# Fermentation Strategies for Production of Pharmaceutical Ternenoids in Engineered Yeast
###### Abstract
They are usually produced from natural resources through extraction or by chemical synthesis, but the obtained yields are generally low due to inherently low level of target compound and the necessity of complex extraction and chemical synthesis methods, which are commercially infeasible [10]. In most cases, the natural production method, extracting terpenoids from original sources (e.g., taxol from yaw tree and artemisinin from the plant _Artemisia annua_) generally fails in terms of quality and supply management due to seasonal and geographical alterations [5]. In addition, plant engineering for terpenoid production is difficult and complex due to tissue specific expression and loss of volatile products by evaporation, and productivity and yields are very low [11]. Due to these limitations, microbial production of terpenoids has received increasing attention, since production of these compounds at large scale fermentation by engineered microorganisms offers a promising higher yield, batch-to-batch consistence, lower production cost, and more sustainability. Among terpenoids, the sesquatieterenoid artemisinin have been often used as an antimalarial drug and the diterpeneoid taxol (paclitaxel) have been developed to be an important anticancer chemotherapy drug for many years [12]. Semi-synthetic artemisinin is currently manufactured by the French pharmaceutical company Sanofi, using engineered _Saccharomyces cerevisiae_ strain developed by Amyris [13], which is a very important example of microbial industrial production of terpenoids. However, the same success has not been yet achieved for paclitaxel due to the complexity of its synthesis pathway, which is still unclear and further studies are required to fully elucidate it [14]. So far, the highest recorded titer of oxygenated taxanes has reached up to 570 mg/L in engineered _Escherichia coli_ by optimizing the P450 expression of taxanes and other related enzymes [15]. For centuries, the baker's yeast, _S. cerevisiae_, has been mainly used in the industrial production of alcoholic beverages (wine, beer, and distilled spirits), bakery products, and bioethanol. However, with the latest developments in synthetic biology, it became one of the most widely industrially used cell factory in the microbial production of a wide variety of products, such as alcohols, organic acids, amino acids, enzymes, therapeutic proteins, chemicals, and metabolites [16]. Among them, for example, biopharmaceutical recombinant peptide hormone, insulin, has been produced by genetically engineered _S. cerevisiae_ strains for many years. Many pharmaceutical companies have chosen this yeast as the most suited host organism to produce a large variety of recombinant products due to its well-known genetics, physiology, biochemistry, and genetic engineering background, the availability of genetic tools, and the suitability of dense and large scale fermentation [16; 17; 18]. In the same line, _S. cerevisiae_ has emerged as a model organism for the production of terpenoids since it has many additional advantages other than mentioned above, such as generally regarded as safe (GRAS) status, high genetic tractability, ease of manipulation, possessing universal endogenous MVA pathway, ability to express eukaryotic cytochrome P450 enzymes, robustness, relatively absence of secondary metabolites, high sugar catabolic, fast growth rate, and high tolerance against harsh industrial conditions [7; 19; 20; 21; 22]. Besides _S. cerevisiae_, other microorganisms have been explored for terpenoids production. Among them, _E. coli_ has the most restrict chassis, since its produces natively limited amounts of terpenoids (e.g., quinones) and, therefore, the improvement of MEP pathway by engineering enzymes for IPP and DMAPP synthesis, or the introduction of heterologous MVA pathway, is required [23]. In contrast, _S. cerevisiae_ has an endogenous MVA pathway, producing high amounts of ergosterol and native cytochrome P450 enzymes for the modification of terpenoids skeleton.