The bio-surfactant mannosylerythritol lipid acts as a selective antibacterial agent to modulate rumen fermentation

Methyl-mannosylerythritol lipid (MEL), a new sugar esterified lipid synthesized by Pseudozyma aphidis, was assessed for its functionality in modulating rumen fermentation and microbiota toward more propionate and less methane production. A pure culture study using rumen representatives showed that MEL selectively inhibited the growth of most Gram-positive bacteria including Streptococcus bovis, ruminococci, and Fibrobacter succinogenes, but not Gram-negative bacteria such as Megasphaera elsdenii, Succinivibrio dextrinosolvens, and Selenomonas ruminantium. A batch culture study revealed that MEL significantly decreased methane production in a dose-dependent manner with accumulation of hydrogen, while propionate production was enhanced. A continuous culture (Rusitec) study confirmed all of these changes. A feeding study revealed that sheep fed a MEL diet showed an increased proportion of propionate, while proportions of acetate and butyrate were decreased without affecting total VFA level. These changes disappeared after cessation of MEL feeding. Based on these results, dietary application of MEL can favorably modify rumen fermentation in terms of the efficiency of dietary energy utilization.

[Naturally engineered glycolipid biosurfactants leading to distinctive self-assembling properties]

Biosurfactants (BS) are functional amphiphilic compounds produced by a variety of microorganisms. They show unique properties (e.g. mild production conditions, lower toxicity, and environmental compatibility) compared to chemically synthesized counterparts. The numerous advantages of BS have prompted applications not only in the food, cosmetic, and pharmaceutical industries but in energy and environmental technologies as well. Mannosylerythritol lipids (MELs) are one of the most promising BS known, and are produced at yields of over 100 g/l from vegetable oils by yeast strains belonging to the genus Pseudozyma. MELs exhibit excellent surface-active and self-assembling properties leading to the formation of different lyotropic liquid crystals such as sponge (L(3)), bicontinuous cubic (V(2)) and lamella (L(alpha)) phases. They also show versatile biochemical actions, including antitumor and differentiation-inducing activities against human leukemia cells, rat pheochromocytoma cells and mouse melanoma cells. MELs also display high binding affinity toward different immunoglobulins and lectins, indicating great potentials as new affinity ligands for the glycoproteins. More significantly, the cationic liposomes bearing MELs increase dramatically the efficiency of gene transfection into mammalian cells via membrane fusion processes. The yeast BS should thus be novel nanobiomaterials, and broaden their applications in various advanced technologies.