Isolation and identification of nematode-antagonistic compounds from the fungus Aspergillus candidus.

Culture medium from an isolate of the fungus Aspergillus candidus was extracted, fractionated and examined to discover compounds antagonistic to plant-parasitic nematodes that are important pathogens of agricultural crops. Column, thin layer and preparative chromatographies and spectral and elemental analyses, were used to isolate and identify two major constituents of an active fraction (Fraction F) obtained from the medium. Compound 1 was identified as 2-hydroxypropane-1, 2, 3-tricarboxylic acid (citric acid). Compound 2 was identified as 3-hydroxy-5-methoxy-3-(methoxycarbonyl)-5-oxopentanoic acid, an isomer of 1, 2-dimethyl citrate. Compound 1 and a citric acid standard, each tested at 50 mg mL(-1) in water, decreased hatch from eggs of the plant-parasitic nematode Meloidogyne incognita by more than 94%, and completely immobilized second-stage juveniles after 4-6 days exposure. Fraction F and Compounds 1 and 2 decreased the mobility of adults of the plant-parasitic nematode Ditylenchus destructor in vitro. Fraction F (25 mg mL(-1)) inhibited mobility >99% at 72 hrs. Compounds 1 and 2 (50 mg mL(-1)) each inhibited mobility more than 25% at 24 hr and more than 50% at 72 hr. This is the first assignment of nematode-antagonistic properties to specifically identified A. candidus metabolites.

The production of succinic acid by yeast Yarrowia lipolytica through a two-step process.

The production of α-ketoglutaric acid by yeast Yarrowia lipolytica VKMY-2412 from ethanol and its subsequent chemical conversion to succinic acid (SA) were investigated. A highly effective and environmentally friendly process of α-ketoglutaric acid production was developed using a special pH-controlling strategy, in which the titration of the culture broth with KOH in the acid-formation phase was minimal, that allowed accumulation of only low amounts of inorganic wastes in the course of SA recovery. The culture broth filtrate containing α-ketoglutaric acid (88.7 g l(-1)) was directly employed for SA production; the amount of SA produced comprised 71.7 g l(-1) with the yield of 70% from ethanol consumed. SA was isolated from the culture broth filtrate in a crystalline form with the purity of 100%. The yield of isolated SA was as high as 72% of its amount in the culture broth filtrate. The antimicrobial and nematocidic effects of SA of microbial origin on pathogenic organisms that cause human and plant diseases were revealed for the first time.