Institute of Process Engineering and Life Sciences, Section II: Technical Biology, Karlsruhe Institute of Technology-KIT, Engler-Bunte-Ring 1, D-76131 Karlsruhe, Germany.
J Biotechnol. 2012 Dec 31;162(4):366-80. doi: 10.1016/j.jbiotec.2012.05.022. Epub 2012 Jun 20.
The demand for bio-based processes and materials in the petrochemical industry has significantly increased during the last decade because of the expected running out of petroleum. This trend can be ascribed to three main causes: (1) the increased use of renewable resources for chemical synthesis of already established product classes, (2) the replacement of chemical synthesis of already established product classes by new biotechnological processes based on renewable resources, and (3) the biotechnological production of new molecules with new features or better performances than already established comparable chemically synthesized products. All three approaches are currently being pursued for surfactant production. Biosurfactants are a very promising and interesting substance class because they are based on renewable resources, sustainable, and biologically degradable. Alkyl polyglycosides are chemically synthesized biosurfactants established on the surfactant market. The first microbiological biosurfactants on the market were sophorolipids. Of all currently known biosurfactants, rhamnolipids have the highest potential for becoming the next generation of biosurfactants introduced on the market. Although the metabolic pathways and genetic regulation of biosynthesis are known qualitatively, the quantitative understanding relevant for bioreactor cultivation is still missing. Additionally, high product titers have been exclusively described with vegetable oil as sole carbon source in combination with Pseudomonas aeruginosa strains. Competitive productivity is still out of reach for heterologous hosts or non-pathogenic natural producer strains. Thus, on the one hand there is a need to gain a deeper understanding of the regulation of rhamnolipid production on process and cellular level during bioreactor cultivations. On the other hand, there is a need for metabolizable renewable substrates, which do not compete with food and feed. A sustainable bioeconomy approach should combine a holistic X-omics strategy with metabolic engineering to achieve the next step in rhamnolipid production based on non-food renewable resources. This review discusses different approaches towards optimization of rhamnolipid production and enhancement of product spectra. The optimization of rhamnolipid production with P. aeruginosa strains, screening methods for new non-pathogenic natural rhamnolipid producers and recombinant rhamnolipid production are examined. Finally, biocatalysis with rhamnolipids for the synthesis of l-rhamnose, β-hydroxyfatty acids, and tailor-made surfactants is discussed. Biosurfactants are still in the phase of initial commercialization. However, for next generation development of rhamnolipid production processes and next generation biosurfactants there are still considerable obstacles to be surmounted, which are discussed here.
在过去的十年中，由于预计石油将耗尽，石化行业对生物基工艺和材料的需求显著增加。这种趋势可以归因于三个主要原因：（1）可再生资源在已有产品类别的化学合成中的使用增加，（2）基于可再生资源的新生物技术工艺替代已有产品类别的化学合成，以及（3）利用新的生物技术生产具有新特性或比已有可比化学合成产品更好性能的新分子。目前都在为表面活性剂的生产而追求这三种方法。生物表面活性剂是一类非常有前途和有趣的物质，因为它们基于可再生资源，可持续且可生物降解。烷基糖苷是在表面活性剂市场上建立的化学合成生物表面活性剂。市场上第一批微生物生物表面活性剂是槐糖脂。在所有目前已知的生物表面活性剂中，鼠李糖脂具有成为下一个推向市场的新一代生物表面活性剂的最高潜力。尽管代谢途径和生物合成的遗传调控在定性上是已知的，但对于生物反应器培养仍然缺乏定量理解。此外，高产物滴度仅在单独使用植物油作为唯一碳源并结合铜绿假单胞菌菌株的情况下才被描述。异源宿主或非致病性天然生产菌株的竞争性生产力仍然遥不可及。因此，一方面需要在生物反应器培养过程中从过程和细胞水平上更深入地了解鼠李糖脂生产的调控。另一方面，需要可代谢的可再生基质，这些基质不会与食物和饲料竞争。可持续的生物经济方法应将整体 X 组学策略与代谢工程相结合，以基于非食品可再生资源实现鼠李糖脂生产的下一步发展。本文讨论了优化鼠李糖脂生产和增强产物谱的不同方法。本文研究了铜绿假单胞菌菌株的鼠李糖脂生产优化、新的非致病性天然鼠李糖脂生产菌的筛选方法和重组鼠李糖脂生产。最后，讨论了利用鼠李糖脂进行 l-鼠李糖、β-羟基脂肪酸和定制表面活性剂的生物催化。生物表面活性剂仍处于初始商业化阶段。然而，对于下一代鼠李糖脂生产工艺和下一代生物表面活性剂的发展，仍有相当多的障碍需要克服，本文对此进行了讨论。
