Mohd Fadzil Fakhrul Ikhma, Mizuno Shoji, Hiroe Ayaka, Nomura Christopher T, Tsuge Takeharu
Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama, Japan.
Department of Chemistry for Life Sciences and Agriculture, Faculty of Life Sciences, Tokyo University of Agriculture, Tokyo, Japan.
Front Bioeng Biotechnol. 2018 Nov 30;6:178. doi: 10.3389/fbioe.2018.00178. eCollection 2018.
Medium-chain-length (MCL) polyhydroxyalkanoates (PHAs) of near homopolymeric composition are unnatural polymers, having almost identical repeating units throughout the polymer chain. These homopolymeric PHAs can be produced by β-oxidation defective bacterial hosts. is an attractive workhorse for the production of such genetically engineered PHAs; however, achieving efficient production of the near homopolymers by β-oxidation defective strains is a major challenge because of a lack of process development studies. In order to address this issue, we investigated the optimization of carbon feeding for efficient production of MCL-PHAs by an strain with defective β-oxidation, LSBJ. Engineered bacteria were cultured in shake-flasks with intermittent feeding of a fatty acid substrate [either decanoate (C10) or dodecanoate (C12)] at various concentrations together with a co-carbon source (glucose, glycerol, or xylose) in order to support cell growth. It was found that feeding low concentrations of both fatty acids and co-carbon sources led to an enhanced production of MCL-PHAs. Additionally, the supplementation of yeast extract improved cell growth, resulting in achieving higher titers of MCL-PHA. As a result, poly(3-hydroxydecanoate) [P(3HD)] and poly(3-hydroxydodecanoate) [P(3HDD)] were produced up to 5.44 g/L and 3.50 g/L, respectively, as near homopolymers by employing the developed feeding strategy. To the best of our knowledge, we record the highest titer of P(3HD) ever reported so far.
具有近均聚组成的中链长度（MCL）聚羟基脂肪酸酯（PHA）是天然聚合物，在整个聚合物链中具有几乎相同的重复单元。这些均聚PHA可由β-氧化缺陷型细菌宿主产生。 是生产此类基因工程PHA的有吸引力的主力菌株；然而，由于缺乏工艺开发研究，通过β-氧化缺陷型菌株高效生产近均聚物是一项重大挑战。为了解决这个问题，我们研究了通过β-氧化缺陷型菌株LSBJ优化碳源进料以高效生产MCL-PHA。将工程菌在摇瓶中培养，间歇添加各种浓度的脂肪酸底物[癸酸（C10）或十二烷酸（C12）]以及共碳源（葡萄糖、甘油或木糖）以支持细胞生长。结果发现，同时添加低浓度的脂肪酸和共碳源可提高MCL-PHA的产量。此外，添加酵母提取物可促进细胞生长，从而实现更高的MCL-PHA滴度。结果，通过采用开发的进料策略，分别以近均聚物形式生产了高达5.44 g/L的聚（3-羟基癸酸酯）[P（3HD）]和3.50 g/L的聚（3-羟基十二烷酸酯）[P（3HDD）]。据我们所知，我们记录了迄今为止报道的P（3HD）的最高滴度。
