Faria Nuno Torres, Santos Marisa, Ferreira Carla, Marques Susana, Ferreira Frederico Castelo, Fonseca César
Department of Bioengineering and IBB - Institute for Bioengineering and Bioscience, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal.
MIT-Portugal Program, 77 Massachusetts Avenue, E40-221, Cambridge, MA, 02139, USA.
Microb Cell Fact. 2014 Nov 4;13:155. doi: 10.1186/s12934-014-0155-7.
Mannosylerythritol lipids (MEL) are glycolipids with unique biosurfactant properties and are produced by Pseudozyma spp. from different substrates, preferably vegetable oils, but also sugars, glycerol or hydrocarbons. However, solvent intensive downstream processing and the relatively high prices of raw materials currently used for MEL production are drawbacks in its sustainable commercial deployment. The present work aims to demonstrate MEL production from cellulosic materials and investigate the requirements and consequences of combining commercial cellulolytic enzymes and Pseudozyma spp. under separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes.
MEL was produced from cellulosic substrates, Avicel® as reference (>99% cellulose) and hydrothermally pretreated wheat straw, using commercial cellulolytic enzymes (Celluclast 1.5 L® and Novozyme 188®) and Pseudozyma antarctica PYCC 5048(T) or Pseudozyma aphidis PYCC 5535(T). The strategies included SHF, SSF and fed-batch SSF with pre-hydrolysis. While SSF was isothermal at 28°C, in SHF and fed-batch SSF, yeast fermentation was preceded by an enzymatic (pre-)hydrolysis step at 50°C for 48 h. Pseudozyma antarctica showed the highest MEL yields from both cellulosic substrates, reaching titres of 4.0 and 1.4 g/l by SHF of Avicel® and wheat straw (40 g/l glucan), respectively, using enzymes at low dosage (3.6 and 8.5 FPU/gglucan at 28°C and 50°C, respectively) with prior dialysis. Higher MEL titres were obtained by fed-batch SSF with pre-hydrolysis, reaching 4.5 and 2.5 g/l from Avicel® and wheat straw (80 g/l glucan), respectively.
This work reports for the first time MEL production from cellulosic materials. The process was successfully performed through SHF, SSF or Fed-batch SSF, requiring, for maximal performance, dialysed commercial cellulolytic enzymes. The use of inexpensive lignocellulosic substrates associated to straightforward downstream processing from sugary broths is expected to have a great impact in the economy of MEL production for the biosurfactant market, inasmuch as low enzyme dosage is sufficient for good systems performance.
甘露糖赤藓糖醇脂（MEL）是具有独特生物表面活性剂特性的糖脂，由假丝酵母属从不同底物中产生，最好是植物油，但也可以是糖、甘油或碳氢化合物。然而，目前MEL生产中高强度的溶剂下游加工以及所用原材料相对较高的价格，是其可持续商业应用的缺点。本研究旨在证明从纤维素材料生产MEL，并研究在单独水解和发酵（SHF）以及同步糖化和发酵（SSF）过程中结合商业纤维素酶和假丝酵母属的要求和后果。
使用商业纤维素酶（Celluclast 1.5 L®和Novozyme 188®）以及南极假丝酵母PYCC 5048(T)或蚜虫假丝酵母PYCC 5535(T)，从纤维素底物、作为参考的微晶纤维素（>99%纤维素）和水热预处理的小麦秸秆中生产MEL。策略包括SHF、SSF和预水解的分批补料SSF。SSF在28°C等温进行，而在SHF和分批补料SSF中，酵母发酵之前在50°C进行48小时的酶促（预）水解步骤。南极假丝酵母从两种纤维素底物中获得的MEL产量最高，通过对微晶纤维素和小麦秸秆（40 g/l葡聚糖）进行SHF，分别达到4.0和1.4 g/l的产量，在28°C和50°C时分别使用低剂量酶（分别为3.6和8.5 FPU/g葡聚糖）并进行预先透析。通过预水解的分批补料SSF获得了更高的MEL产量，从微晶纤维素和小麦秸秆（80 g/l葡聚糖）分别达到4.5和2.5 g/l。
本研究首次报道了从纤维素材料生产MEL。该过程通过SHF、SSF或分批补料SSF成功进行，为达到最佳性能，需要使用经过透析的商业纤维素酶。与从含糖肉汤进行直接下游加工相关的廉价木质纤维素底物的使用，预计将对生物表面活性剂市场中MEL生产的经济性产生重大影响，因为低酶剂量足以实现良好的系统性能。
