Laboratory for Biomaterials, Swiss Federal Laboratories for Materials Science and Technology (Empa), Gallen, Switzerland.
BMC Biotechnol. 2012 Aug 22;12:53. doi: 10.1186/1472-6750-12-53.
Pseudomonas putida KT2440 is able to synthesize large amounts of medium-chain-length polyhydroxyalkanoates (mcl-PHAs). To reduce the substrate cost, which represents nearly 50% of the total PHA production cost, xylose, a hemicellulose derivate, was tested as the growth carbon source in an engineered P. putida KT2440 strain.
The genes encoding xylose isomerase (XylA) and xylulokinase (XylB) from Escherichia coli W3110 were introduced into P. putida KT2440. The recombinant KT2440 exhibited a XylA activity of 1.47 U and a XylB activity of 0.97 U when grown on a defined medium supplemented with xylose. The cells reached a maximum specific growth rate of 0.24 h(-1) and a final cell dry weight (CDW) of 2.5 g L(-1) with a maximal yield of 0.5 g CDW g(-1) xylose. Since no mcl-PHA was accumulated from xylose, mcl-PHA production can be controlled by the addition of fatty acids leading to tailor-made PHA compositions. Sequential feeding strategy was applied using xylose as the growth substrate and octanoic acid as the precursor for mcl-PHA production. In this way, up to 20% w w(-1) of mcl-PHA was obtained. A yield of 0.37 g mcl-PHA per g octanoic acid was achieved under the employed conditions.
Sequential feeding of relatively cheap carbohydrates and expensive fatty acids is a practical way to achieve more cost-effective mcl-PHA production. This study is the first reported attempt to produce mcl-PHA by using xylose as the growth substrate. Further process optimizations to achieve higher cell density and higher productivity of mcl-PHA should be investigated. These scientific exercises will undoubtedly contribute to the economic feasibility of mcl-PHA production from renewable feedstock.
恶臭假单胞菌 KT2440 能够大量合成中链长度聚羟基脂肪酸酯（mcl-PHAs）。为了降低占 PHAs 生产成本近 50%的底物成本，我们测试了木聚糖，一种半纤维素衍生物，作为工程化恶臭假单胞菌 KT2440 菌株的生长碳源。
从大肠杆菌 W3110 中引入了编码木糖异构酶（XylA）和木酮糖激酶（XylB）的基因。重组 KT2440 在补充木糖的限定培养基中生长时，XylA 活性为 1.47 U，XylB 活性为 0.97 U。细胞达到最大比生长速率 0.24 h(-1)，最终细胞干重（CDW）为 2.5 g L(-1)，最大木糖得率为 0.5 g CDW g(-1)木糖。由于木糖中没有积累 mcl-PHA，因此可以通过添加脂肪酸来控制 mcl-PHA 的生产，从而获得定制的 PHA 组成。采用顺序进料策略，以木糖为生长底物，辛酸为 mcl-PHA 生产的前体。通过这种方式，可以获得高达 20% w w(-1)的 mcl-PHA。在采用的条件下，每克辛酸可获得 0.37 g mcl-PHA。
相对廉价的碳水化合物和昂贵的脂肪酸的顺序进料是实现更具成本效益的 mcl-PHA 生产的一种实用方法。本研究首次尝试使用木糖作为生长底物生产 mcl-PHA。应进一步优化工艺，以提高细胞密度和 mcl-PHA 的生产力。这些科学研究无疑将有助于从可再生原料生产 mcl-PHA 的经济可行性。
