Production of different types of mannosylerythritol lipids as biosurfactants by the newly isolated yeast strains belonging to the genus Pseudozyma

Abstract

Mannosylerythritol lipids (MEL), which are abundantly secreted by yeasts, are one of the most promising biosurfactants known. To obtain various types of MEL and to attain a broad range of applications for them, screening of novel producers was undertaken. Thirteen strains of yeasts were successfully isolated as potential MEL producers; they showed high production yields of MEL of around 20 g l(-1) from 40 g l(-1) of soybean oil. Based on the taxonomical study, all the strains were classified to be the genus Pseudozyma. It is interesting to note that they were categorized into three groups according to their production patterns of MEL. The first group, which included 11 strains taxonomically closely related to high-level MEL producers such as Pseudozyma antarctica and Pseudozyma aphidis, mainly produced 4-O-[(4',6'-di-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl]-meso-erythritol (MEL-A) together with 4-O-[(6'-mono-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl]-meso-erythritol (MEL-B) and 4-O-[(4'-mono-O-acetyl-2',3'-di-O-alkanoyl)-beta-D-mannopyranosyl]-meso-erythritol (MEL-C) as the minor components. The second group of one strain, which was related to Pseudozyma tsukubaensis, predominantly produced MEL-B. The third group of one strain, which was closely related to Pseudozyma hubeiensis, mainly produced MEL-C; this is the first observation of the efficient production of MEL-C from soybean oil. Moreover, the major fatty acids of the obtained MEL-C were C(6), C(12), and C(16) acids, and were considerably different from those of the other MEL hitherto reported. The biosynthetic manner for MEL is thus likely to significantly vary among the Pseudozyma strains; the newly isolated strains would enable us to attain a large-scale production of MEL and to obtain various types of MEL with different hydrophobic structures.

Biosurfactant-producing yeasts widely inhabit various vegetables and fruits

“…KM-160 19) used in this study were isolated as MEL-A and MEL-B producer respectively, as reported previously. Pseudozyma tsukubaensis JCM 10324…”

“…The concentrated glycolipids were dissolved in chloroform and then purified by silica gel (Wako-gel C-200) column chromatography with a gradient elution of a chloroform/acetone (10:0 to 0:10, v/v) mixture as solvent system. 19) The purified glycolipids were used in subsequent experiments.…”

“…In the NMR study, purified MEL-A and MEL-B prepared, as reported previously, were used as references. 19,20) The molecular weight of the purified glycolipid was measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) (Voyager-DE PRO, Applied Biosystems, Foster City, CA) with an α-cyano-4-hdroxycinnamic acid matrix. The fatty acid profiles of the purified glycolipids were examined by gas chromatography/mass spectrometry (GC/MS), as previously reported.…”

“…The fatty acid profiles of the purified glycolipids were examined by gas chromatography/mass spectrometry (GC/MS), as previously reported. 19) Methyl ester derivatives of fatty acids were prepared by mixing the above-mentioned purified glycolipids (10 mg) with 5% HCl/methanol regent (1 mL) (Wako, Tokyo) at 80°C over 3 h. After the reaction was quenched with water (1 mL), the methyl ester derivatives were extracted with n-hexane and then analyzed by GC/MS (Hewlett Packard 6890 and 5973 N, Agilent Technologies, Tokyo) with a capillary column (TC-WAX, GL-Science, Tokyo) with a temperature gradient programmed from 90°C (held for 3 min) to 240°C at 5°C/min. All regents and solvents are commercially available and were used as received.…”

“…Purified MEL-A, MEL-B, and MEL-C, prepared as reported previously, were used as standard. [18][19][20] All measurements reported here represent means for at least three independent experiments.…”