Date Published: May 5, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Yohanes Eko Chandra Sugiharto, Heeseok Lee, Annur Dyah Fitriana, Hyeokwon Lee, Wooyoung Jeon, Kyungmoon Park, Jungoh Ahn, Hongweon Lee.
Biotransformation of fatty acid methyl esters to dicarboxylic acids has attracted much attention in recent years; however, reports of sebacic acid production using such biotransformation remain few. The toxicity of decanoic acid is the main challenge for this process. Decane induction has been reported to be essential to activate the enzymes involved in the α,ω-oxidation pathway before initiating the biotransformation of methyl decanoate to sebacic acid. However, we observed the accumulation of intermediates (decanoic acid and 10-hydroxydecanoic acid) during the induction period. In this study, we examined the effects of these intermediates on the biotransformation process. The presence of decanoic acid, even at a low concentration (0.2 g/L), inhibited the transformation of 10-hydroxydecanoic acid to sebacic acid. Moreover, about 24–32% reduction in the decanoic acid oxidation was observed in the presence of 0.5–1.5 g/L 10-hydroxydecanoic acid. To eliminate these inhibitory effects, we applied substrate-limiting conditions during the decane induction process, which eliminated the accumulation of decanoic acid. Although the productivity of sebacic acid (34.5 ± 1.10 g/L) was improved, by 28% over that achieved using the previously methods, after 54 h, the accumulation of 10-hydroxydecanoic acid was still detected. The accumulation of 10-hydroxydecanoic acid even under the decane limiting conditions could be an evidence that oxidation of 10-hydroxydecanoic acid could be the rate-limiting step in this process. The improvement of this reaction should be an important objective for further development of the production of sebacic acid using biotransformation.
Sebacic acid, a 10 carbon containing dicarboxylic acid (DCA), is an important precursor in the production of nylon and polyamides (PAs), primarily PA-4,10 and PA-5,10 (Chung et al. 2015). Like other medium-chain DCAs, the commercial process for the production of sebacic acid depends on chemical methods, principally involving alkaline oxidation of vegetable oils, such as castor oil, in which 2-octanol is generated as a byproduct (Green et al. 2000; Azcan and Demirel 2008; Metzger 2009). However, the production of medium-chain DCAs through chemical routes has several problems, particularly the use of harsh production conditions and generation of by-products. Biological processes for the production of DCAs can overcome these limitations because they require milder conditions (Huf et al. 2011; Song et al. 2013).
As observed in previous studies, decane induction was necessary for the activation of enzymes involved in the α,ω-oxidation pathway prior to the biotransformation of methyl decanoate to sebacic acid (Beardslee et al. 2014). In a preliminary test (Additional file 1: Figure S1), the possibility of using potassium decanoate (represented as decanoic acid) or methyl decanoate as inducers for these enzymes was examined in flask cultures. The results of this experiment confirmed that the toxicity of decanoic acid interferes with the activation and even inactivates the cells (when potassium decanoate or methyl decanoate were used as inducers at concentrations as low as 0.4 g/L). In contrast, this negative trend was not observed when decane was used for induction. Therefore, decane induction was inevitable for the biotransformation of methyl decanoate to sebacic acid.