Long-chain dicarboxylic acids (DCAs) are versatile chemical intermediates used as building blocks for the production of adhesives, lubricants, resins, plastics, polyesters, nylons, adhesives, antiseptics, and perfumes. Industrial long-chain DCAs are mainly produced from petro-chemical resources. An alternative is the biotechnological production from renewable materials like plant oil FAs by microbial fermentation using oleogenious yeasts.
Strains and Substrates
Oleogenious yeasts like Candida tropicalis or Yarrowia lipolytica not only have the natural ability to accumulate high amounts of lipids, but also to produce long-chain DCAs from hydrophobic substrates. Besides, S. cerevisiae and E. coli are two major stains to produce long-chain DCAs. The common strains and substrates to produce long-chain DCAs are listed in table 1[1].
Table 1 Examples for DCA production yields with different microbial systems using hydrophobic substrates
| Strain | Substrate | Produced DCA (g/L) | Strain | Substrate | Produced DCA (g/L) |
|---|
| C. viswanathii | Dodecane (C12) | 140 | C. cloacae | Coconut oil | 11 |
| Methyl tetradecanoate (C14) | 210 | Lauric acid (C12) | 10 |
| Oleic acid (C18) | 100 | P. aeruginosa | Pentadecane (C15) | 0.48 |
| Y. lipolytica | Sunflower oil | 23 | E. coli | C12-fatty acid | 0.16 |
| C. maltosa | Tridecane (C13) | 15 | C14-fatty acid | 0.41 |
| S. bombicola | Octadecane (C18) | 5.6 | S. cerevisiae | Lauric acid (C12) | No data available |
| C. neoformans | Pentadecane (C15) | 0.61 | | | |
Biosynthetic Process
We took oleogenious yeasts for example to describe the metabolic processes involved in the production of long-chain DCAs. The three main steps of this process are i) uptake of hydrophobic substrates and the conversion of alkanes to FAs during primary alkane oxidation, ii) the main degradation through β-oxidation, and iii) with their alternative conversion to DCAs via ω-oxidation and subsequent break down.
- Uptake of hydrophobic substrates and primary alkane oxidation to FAs
Fig. 1 Uptake of hydrophobic substrates
and primary alkane oxidation
Alkanes are converted to FAs of the same chain length, taking place in the endoplasmatic reticulum (ER) or the peroxisomes (Figure 1)[1]. Firstly, n-alkanes are oxidized by a cytochrome P450 monooxigenase/NADPH-dependent cytochrome P450 reductase complex (CYP, NCP) to the corresponding fatty-alcohol in ER. Secondly, the fatty-alcohol is converted into FA in a two-step process which involves a fatty-alcohol dehydrogenase (ADH) or a fatty acid oxidase (FAO), and a fatty-aldehyde dehydrogenase (FALDH). By the way, before uptake triacylglycerol (TAG) is hydrolyzed by extracellular lipases to free FAs. FAs can be stored intracellularly in lipid bodies (LB) as neutral lipids (triacylglycerol or steryl ester (STE)).
- Degradation of FAs via β-oxidation
In yeasts, FAs are further degraded through β-oxidation by stepwise break down to acetyl-CoA in the peroxisomes. This process consists out of four biochemical steps performed by three enzymes that are repeated in a cyclic manner. four-step β-oxidation sequence involves an acyl-CoA oxidase (POX), an enoyl-CoA hydratase and 2-hydroxyacyl-CoA dehydrogenase (MFE), and a 3-ketoacyl-CoA thiolase (POT1).
- Biosynthesis of dicarboxylic acids via ω-oxidation
In addition, FAs can be converted via ω-oxidation to DCAs in the ER. The FA is oxidized into the corresponding ω-hydroxy FA in the Cω -position by the ω-hydroxylase complex built by a cytochrome P450 monooxygenase (CYP or ALK) and an NADPH-dependent cytochrome P450 reductase (NCP). The ω-hydroxy FA is further oxidized by ADH or FAO to the fatty-aldehyde. The aldehyde group is then further converted to the carboxy group of the DCA by a FALDH.
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Reference
- Nicole Werner, Susanne Zibek. Biotechnological production of bio-based long-chain dicarboxylic acids with oleogenious yeasts. World J Microbiol Biotechnol (2017) 33:194.
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