Laboratory of Plant Pathology, Multidisciplinary Institute for Environmental Studies (MIES) Ramón Margalef, Department of Marine Sciences and Applied Biology, University of Alicante, E-03080 Alicante, Spain.
Mol Microbiol. 2010 Feb;75(4):1021-32. doi: 10.1111/j.1365-2958.2009.07039.x.
The antifungal mode of action of chitosan has been studied for the last 30 years, but is still little understood. We have found that the plasma membrane forms a barrier to chitosan in chitosan-resistant but not chitosan-sensitive fungi. The plasma membranes of chitosan-sensitive fungi were shown to have more polyunsaturated fatty acids than chitosan-resistant fungi, suggesting that their permeabilization by chitosan may be dependent on membrane fluidity. A fatty acid desaturase mutant of Neurospora crassa with reduced plasma membrane fluidity exhibited increased resistance to chitosan. Steady-state fluorescence anisotropy measurements on artificial membranes showed that chitosan binds to negatively charged phospholipids that alter plasma membrane fluidity and induces membrane permeabilization, which was greatest in membranes containing more polyunsaturated lipids. Phylogenetic analysis of fungi with known sensitivity to chitosan suggests that chitosan resistance may have evolved in nematophagous and entomopathogenic fungi, which naturally encounter chitosan during infection of arthropods and nematodes. Our findings provide a method to predict the sensitivity of a fungus to chitosan based on its plasma membrane composition, and suggests a new strategy for antifungal therapy, which involves treatments that increase plasma membrane fluidity to make fungi more sensitive to fungicides such as chitosan.
壳聚糖的抗真菌作用模式已经研究了 30 年，但仍知之甚少。我们发现，在壳聚糖抗性真菌中，质膜形成了对壳聚糖的屏障，但在壳聚糖敏感真菌中则没有。壳聚糖敏感真菌的质膜比壳聚糖抗性真菌具有更多的多不饱和脂肪酸，这表明壳聚糖对其的通透性可能依赖于膜流动性。粗糙脉孢菌（Neurospora crassa）的一种脂肪酸去饱和酶突变体，其质膜流动性降低，对壳聚糖的抗性增加。在人工膜上进行的稳态荧光各向异性测量表明，壳聚糖与带负电荷的磷脂结合，改变质膜流动性并诱导膜通透性增加，在含有更多多不饱和脂质的膜中增加最大。对已知对壳聚糖敏感的真菌进行系统发育分析表明，壳聚糖抗性可能是在食线虫真菌和昆虫病原真菌中进化而来的，这些真菌在感染节肢动物和线虫时自然会遇到壳聚糖。我们的发现为基于真菌质膜组成预测其对壳聚糖的敏感性提供了一种方法，并为抗真菌治疗提供了一种新策略，即通过增加质膜流动性使真菌对杀真菌剂（如壳聚糖）更敏感的治疗方法。
