Ulm Center for Peptide Pharmaceuticals (U-PEP), Ulm University, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
Institute for Molecular Enzyme Technology (IMET), Heinrich-Heine-University Düsseldorf, Forschungszentrum Jülich GmbH, Wilhelm-Johnen-Straße, 52428, Jülich, Germany.
Appl Microbiol Biotechnol. 2018 Feb;102(3):1229-1239. doi: 10.1007/s00253-017-8702-x. Epub 2017 Dec 20.
Rhamnolipids are biosurfactants consisting of rhamnose (Rha) molecules linked through a β-glycosidic bond to 3-hydroxyfatty acids with various chain lengths, and they have an enormous potential for various industrial applications. The best known native rhamnolipid producer is the human pathogen Pseudomonas aeruginosa, which produces short-chain rhamnolipids mainly consisting of a Rha-Rha-C-C congener. Bacteria from the genus Burkholderia are also able to produce rhamnolipids, which are characterized by their long-chain 3-hydroxyfatty acids with a predominant Rha-Rha-C-C congener. These long-chain rhamnolipids offer different physicochemical properties compared to their counterparts from P. aeruginosa making them very interesting to establish novel potential applications. However, widespread applications of rhamnolipids are still hampered by the pathogenicity of producer strains and-even more important-by the complexity of regulatory networks controlling rhamnolipid production, e.g., the so-called quorum sensing system. To overcome encountered challenges of the wild type, the responsible genes for rhamnolipid biosynthesis in Burkholderia glumae were heterologously expressed in the non-pathogenic Pseudomonas putida KT2440. Our results show that long-chain rhamnolipids from Burkholderia spec. can be produced in P. putida. Surprisingly, the heterologous expression of the genes rhlA and rhlB encoding an acyl- and a rhamnosyltransferase, respectively, resulted in the synthesis of two different mono-rhamnolipid species containing one or two 3-hydroxyfatty acid chains in equal amounts. Furthermore, mixed biosynthetic rhlAB operons with combined genes from different organisms were created to determine whether RhlA or RhlB is responsible to define the fatty acid chain lengths in rhamnolipids.
鼠李糖脂是由鼠李糖（Rha）分子通过β-糖苷键连接到具有不同链长的 3-羟基脂肪酸组成的生物表面活性剂，具有巨大的各种工业应用潜力。最著名的天然鼠李糖脂生产者是人类病原体铜绿假单胞菌，它主要产生由 Rha-Rha-C-C 同系物组成的短链鼠李糖脂。伯克霍尔德氏菌属的细菌也能够产生鼠李糖脂，其特征是长链 3-羟基脂肪酸主要由 Rha-Rha-C-C 同系物组成。与来自铜绿假单胞菌的对应物相比，这些长链鼠李糖脂具有不同的物理化学性质，这使得它们非常有趣，可以建立新的潜在应用。然而，鼠李糖脂的广泛应用仍然受到产生菌株的致病性的阻碍，甚至更重要的是，受到控制鼠李糖脂产生的调控网络的复杂性的阻碍，例如所谓的群体感应系统。为了克服野生型遇到的挑战，在非致病性假单胞菌 KT2440 中异源表达了导致根瘤菌属 glumae 产生鼠李糖脂的相关基因。我们的结果表明，根瘤菌属 spec.的长链鼠李糖脂可以在假单胞菌属 putida 中产生。令人惊讶的是，分别编码酰基转移酶和鼠李糖基转移酶的基因 rhlA 和 rhlB 的异源表达导致了两种不同的单鼠李糖脂的合成，其中含有一个或两个 3-羟基脂肪酸链，数量相等。此外，创建了具有不同生物体组合基因的混合生物合成 rhlAB 操纵子，以确定 RhlA 或 RhlB 负责定义鼠李糖脂中的脂肪酸链长。
