Extracellular cellobiose lipid from yeast and their analogues: structures and fungicidal activities

Basidiomycetous yeasts Cryptococcus humicola and Pseudozyma fusiformata secrete cellobiose lipids into the culture broth. In the case of Cr. humicola, 16-(tetra-O-acetyl-beta-cellobiosyloxy)-2-hydroxyhexadecanoic acid was defined as major product and 16-(tetra-O-acetyl-beta-cellobiosyloxy)-2,15-dihydrohexadecanoic acid was defined as minor product, while Ps. fusiformata secreted mainly 16-[6-O-acetyl-2'-O-(3-hydroxyhexanoyl)-beta-cellobiosyloxy)-2,15-dihydroxyhexadecanoic acid. These compounds exhibit similar fungicidal activities against different yeasts including pathogenic Cryptococcus and Candida species. The cells of Filobasidiella neoformans causing systemic cryptococcosis completely died after 30-min incubation with 0.02 mg mL(-1) of cellobiose lipids. The same effect on ascomycetous yeast, including pathogenic Candida species, is achieved at 0.1-0.3 mg mL(-1) of cellobiose lipids depending on the test culture used. Cellobiose lipid of Ps. fusiformata inhibits the growth of phytopathogenic fungi Sclerotinia sclerotiorum and Phomopsis helianthi more efficiently than cellobiose lipids from Cr. humicola. Fully O-deacylated analogue, namely 16-(beta-cellobiosyloxy)-2-hydroxyhexadecanoic acid, and totally synthetic compound, 16-(beta-cellobiosyloxy)-hexadecanoic acid, do not inhibit the growth of F. neoformans and Saccharomyces cerevisiae, while 16-(beta-cellobiosyloxy)-2,15-dihydroxyhexadecanoic acid inhibits the growth of both test cultures but at higher concentrations than cellobiose lipids of Cr. humicola and Ps. fusiformata. The amide of 16-(beta-cellobiosyloxy)-2,15-dihydroxyhexadecanoic acid possessed no fungicide activity. Thus, the structures of both the carbohydrate part and fatty acid aglycon moiety are important for the fungicidal activity of cellobiose lipids.