numbers of 58), it forms the precursor for jet biofuel (Yang et al., 2016). Its market size was reported to be 8.51‐kilotons in 2015 and is expected to reach 180.9 kilotons and up to $485 million by 2023. Amyris Biotechnologies, USA, dominates the global farnesene market (Biofene). Intrexon and chromatin, USA, is in emerging state to reach production level. Farnesene is basically synthesized by plants. So, adding this machinery to the prokaryotes will increase its production. E. coli, S. cerevisiae, and Yarrowia lypolytica are heterotrophic organisms that were engineered by adding farnesene synthase gene to produce farnesene (Wang et al., 2011; Tippmann et al., 2016; Yang et al., 2016). The heterotrophic organisms require continuous supply of carbon sources. Therefore, using cyanobacteria, i.e. autotrophic organisms can be beneficial as they utilize carbon dioxide as the carbon source and also helps in CO2 sequestration. Table 1.2 shows the list of photosynthetic organisms engineered to produce farnesene. Much research is needed to be done in the field of farnesene synthesis and is a booming biofuel.
Table 1.1 Genome wide analysis of terpene synthase genes.
| Plant species | Description | References |
|---|---|---|
| Jatropha curcas | 59 putative TPS genes were identified.Among them 26 belongs to TPS‐a family. | Xiong et al. (2016) |
| Ananas comosus | 21 putative TPS genes were identified.Divided into five sub families. | Chen et al. (2017) |
| Citrus sinensis | 55 putative TPS genes identified out of which 28 are TPS‐A, 18 are TPS‐b, and 5 are TPS‐g.Only two of them are TPS‐e/f each. | Alquezar et al. (2017) |
| Ocimum sanctum | 81 putative genes identified.Further only 47 putative genes were found to be functional. | Kumar et al. (2018) |
Table 1.2 Photoautotrophic production of farnesene.
| Microorganism | Promoter used | Description | Max. farnesene concentration (mg/l) | References |
|---|---|---|---|---|
| Anabaena sp. PCC 7120 | Ptrc | Codon optimized farnesene synthase gene from Norway spruce is taken.Expression plasmid was used for the production. | 0.0691 | Halfmann et al., (2014) |
| Synechococcus elongatus PCC 7942 | Ptrc | Codon optimized farnesene synthase gene from Malus domestica and Picea abies was taken.In addition to the above‐mentioned genes dxs, idi and ispA gene were also incorporated int the genome. Thus, optimizing Methylerithritol phosphate (MEP) pathway. | 4.6 ± 0.4 | Lee et al., (2017) |
dxs, deoxy xylulose synthase; idi, isopentynyl pyrophosphate isomerase; ispA, farnesyl diphosphate synthase.
Isoprene (C5H8) is another industrially important chemical. It is a volatile hydrocarbon produced by plants under stress condition. One million tons of it is produced from petrochemicals to reach the global need (Morais et al., 2015). Isolating such huge amount of isoprene from plants is not feasible. Therefore, microbial production of isoprene is gaining interest recently. Cyanobacteria are genetically modified for isoprene synthase (Isps) gene, which is usually absent in them. Isoprene synthase gene catalyzes the conversion of di‐methylallyl diphosphate to isoprene. Lindberg et al., (2010) reported first isoprene synthesis from cyanobacteria. Isps gene from Pueraria montana was introduced in PCC6803 under the light‐regulated PsbA2 promoter giving yield of isoprene 50 μg/g DCW. Engineering isoprene synthase gene with other MVA pathway genes improves yield of isoprene by 2.5‐folds (Bentley et al., 2014). Apart from introduction of isoprene synthase gene, overexpression of IPP isomerase (IDI) gene leads to 40% photosynthetically fixed carbon toward isoprene (Gao et al., 2016b).
1.5 Conclusion
Biocommodities are now being produced by microbial cell factories. These microorganisms are engineered to increase their robustness. Increasing knowledge of the omics technologies as now we have full access to whole genome makes easy to manipulate any organism. Engineering of microbial cell factories depends on the required end product. Number of genetic tools are now available that makes biocommodity engineering easy. Despite of the plethora of literature available on genetic engineering of microorganisms, very few of them are able to perform well industrially. Therefore, focus is to be made on scale up of the existing cell factories, and new engineered strains should also be taken to industrial level for better production.
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