中长链聚羟基脂肪酸酯（mcl-PHA）是一大类由微生物合成的天然生物聚酯,因具有可再生性和生物降解性愈来愈受到人们的关注。Mcl-PHA可由一些假单胞菌利用自身的脂肪酸合成途径或β-氧化途径来合成。耶氏解脂酵母具有很好的脂/脂肪酸分解代谢能力,但是它体内缺乏PHA合成酶（intrinsic）不能合成mcl-PHA。本文采用代谢工程策略构建重组解脂酵母,外源表达来自铜绿假单胞菌PAO1（P.aeruginosa PAO1）的PHA合成酶基因PhaC1。在PhaC1基因的末端添加PTS1过氧化物酶体定位信号序列,使其在过氧化物酶体内发挥功能。利用pINA1312载体构建表达框,借助载体上的zeta序列元件将PhaC1基因表达框整合至酵母基因组,完成基因的稳定表达。重组菌PSOC在葡萄糖为唯一碳源的培养基中几乎不产PHA,添加0.5%的油酸时可合成占细胞干重0.67%的mcl-PHA。在含三油酸甘油酯的培养基中发酵72 h产生1.51%PHA。本实验表明解脂酵母成为有潜力的生产细胞工厂,在将来可以利用一些食品厨余垃圾等富含油脂的廉价资源生产mcl-PHA。

Establishing of a bio-based and green society depends on the availability of inexpensive organic carbon compounds, which can be converted by microbes into various valuable products. Around 3.7 x 10(9) t of agricultural residues and 1.3 x 10(9) t of food residues occur annually worldwide. This enormous amount of organic material is basically considered as waste and incinerated, anaerobically digested or composted for the production of heat, power or fertilizers. However, organic residues can be used as nutrient sources in biotechnological processes. For example, organic residues can be hydrolyzed to glucose, amino acids and phosphate by chemical and/or biological methods, which are utilizable as nutrients by many microbes. This approach paves the way toward the establishment of a bio-based economy and an effective organic residues valorization for the formation of bio-based chemicals and materials. In this review, valorization of organic residues in biotechnological processes is presented. The focus is on the production of three industrially important added value chemicals, namely succinic acid, lactic acid and fatty acid based plasticizer, which have been used for the synthesis of environmentally benign materials and food supplements. Furthermore, utilization strategies of residues coming from fruit and vegetable processing are introduced. (C) 2015 Elsevier B.V. All rights reserved.

Background: Integrating waste management with fuels and chemical production is considered to address the food waste problem and oil crisis. Approximately, 600 million tonnes crude glycerol is produced from the biodiesel industry annually, which is a top renewable feedstock for succinic acid production. To meet the increasing demand for succinic acid production, the development of more efficient and cost-effective production methods is urgently needed. Herein, we have proposed a new strategy for integration of both biodiesel and SA production in a biorefinery unit by construction of an aerobic yeast Yarrowia lipolytica with a deletion in the gene coding succinate dehydrogenase subunit 5.Results: Robust succinic acid production by an engineered yeast Y. lipolytica from crude glycerol without pretreatment was demonstrated. Diversion of metabolic flow from tricarboxylic acid cycle led to the success in generating a succinic acid producer Y. lipolytica PGC01003. The fermentation media and conditions were optimized, which resulted in 43 g L-1 succinic acid production from crude glycerol. Using the fed-batch strategy in 2.5 L fermenter, up to 160 g L-1 SA was yielded, indicating the great industrial potential.Conclusions: Inactivation of SDH5 in Y. lipolytica Po1f led to succinic acid accumulation and secretion significantly. To our best knowledge, this is the highest titer obtained in fermentation on succinic acid production. In addition, the performance of batch and fed-batch fermentation showed high tolerance and yield on biodiesel by-product crude glycerol. All these results indicated that PGC01003 is a promising microbial factorial cell for the highly efficient strategy solving the environmental problem in connection with the production of value-added product.

Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) are a large class of biopolymers that have attracted extensive attention as renewable and biodegradable bio-plastics. They are naturally synthesized via fatty acid de novo biosynthesis pathway or beta-oxidation pathway from Pseudomonads. The unconventional yeast Yarrowia lipolytica has excellent lipid/fatty acid catabolism and anabolism capacity depending of the mode of culture. Nevertheless, it cannot naturally synthesize PHA, as it does not express an intrinsic PHA synthase. Here, we constructed a genetically modified strain of Y. lipolytica by heterologously expressing PhaC1 gene from P. aeruginosa PAO1 with a PTS1 peroxisomal signal. When in single copy, the codon optimized PhaC1 allowed the synthesis of 0.205 % DCW of PHA after 72 h cultivation in YNBD medium containing 0.1 % oleic acid. By using a multi-copy integration strategy, PHA content increased to 2.84 % DCW when the concentration of oleic acid in YNBD was 1.0 %. Furthermore, when the recombinant yeast was grown in the medium containing triolein, PHA accumulated up to 5.0 % DCW with as high as 21.9 g/L DCW, which represented 1.11 g/L in the culture. Our results demonstrated the potential use of Y. lipolytica as a promising microbial cell factory for PHA production using food waste, which contains lipids and other essential nutrients.

Mixed food waste, which was directly collected from restaurants without pretreatments, was used as a valuable feedstock in succinic acid (SA) fermentation in the present study. Commercial enzymes and crude enzymes produced from Aspergillus awamori and Aspergillus oryzae were separately used in hydrolysis of food waste, and their resultant hydrolysates were evaluated. For hydrolysis using the fungal mixture comprising A. awamori and A. oryzae, a nutrient-complete food waste hydrolysate was generated, which contained 31.9 g L-1 glucose and 280 mg L-1 free amino nitrogen. Approximately 80-90 % of the solid food waste was also diminished. In a 2.5 L fermentor, 29.9 g L-1 SA was produced with an overall yield of 0.224 g g(-1) substrate using food waste hydrolysate and recombinant Escherichia coli. This is comparable to many similar studies using various wastes or by-products as substrates. Results of this study demonstrated the enormous potential of food waste as renewable resource in the production of bio-based chemicals and materials via microbial bioconversion.