Mimee Benjamin, Labbé Caroline, Bélanger Richard R
Centre de Recherche en Horticulture, Université Laval, Québec G1V 0A6, Canada.
Glycobiology. 2009 Sep;19(9):995-1001. doi: 10.1093/glycob/cwp078. Epub 2009 Jun 3.
Flocculosin is an unusual cellobiose lipid secreted by the yeast-like fungus Pseudozyma flocculosa as part of its biocontrol arsenal against other fungi. Recent observations have suggested that the fungus degrades flocculosin to use it as a nutrient source during periods of food limitation. In this work, we sought to identify the catabolic steps leading to the degradation of flocculosin and its subsequent use by P. flocculosa. To this end, we characterized the catabolism of flocculosin through identification of degradation intermediates in a deprived medium using mass spectrometry. As the pH of the medium increased, the molecule was quickly deacylated and lost its antimicrobial activity thereby explaining conflicting results concerning the antimicrobial activity of this class of glycolipid. Following removal of both acetyl groups and the short fatty acid chain under alkaline conditions, the molecule was quickly and completely metabolized by P. flocculosa. Protein purification of culture filtrates confirmed the presence of degradative enzymes produced by P. flocculosa. These enzymes were found to degrade 3,15-dihydroxy-hexadecyl cellobioside (DHC) but not the acylated molecule, thus confirming the protective role of these groups against catabolism. These results are the first evidence of glycolipid degradation by producing organism and suggest that flocculosin can be recycled by P. flocculosa as a nutrient in addition to protecting its ecological niche.
絮凝菌素是一种由类酵母真菌絮凝假丝酵母分泌的特殊纤维二糖脂，是其对抗其他真菌的生物防治武器库的一部分。最近的观察表明，在食物匮乏时期，该真菌会降解絮凝菌素以将其用作营养源。在这项研究中，我们试图确定导致絮凝菌素降解及其随后被絮凝假丝酵母利用的分解代谢步骤。为此，我们通过使用质谱法鉴定贫养培养基中的降解中间体来表征絮凝菌素的分解代谢。随着培养基pH值的升高，该分子迅速脱酰基并失去其抗菌活性，从而解释了关于这类糖脂抗菌活性的相互矛盾的结果。在碱性条件下去除两个乙酰基和短脂肪酸链后，该分子被絮凝假丝酵母迅速且完全代谢。对培养滤液进行蛋白质纯化证实了絮凝假丝酵母产生的降解酶的存在。发现这些酶可降解3,15 - 二羟基十六烷基纤维二糖苷（DHC），但不能降解酰化分子，从而证实了这些基团对分解代谢的保护作用。这些结果是产生该物质的生物体降解糖脂的首个证据，并表明絮凝菌素除了保护其生态位外，还可被絮凝假丝酵母作为营养物质循环利用。
