Antarctic yeasts: potential use in a biologic treatment of textile azo dyes.

We investigated the dye-removal potential of a collection of 61 cold-adapted yeasts from the King George Island, Antarctica, on agar plates supplemented with 100 mg L-1 of several textile dyes; among which isolates 81% decolorized Reactive Black 5 (RB-5), with 56% decolorizing Reactive Orange 16, but only 26% doing so with Reactive Blue 19 and Acid Blue 74. Furthermore, we evaluated the ligninolytic potential using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic-acid) diammonium salt-, 3,5-dimethoxy-4-hydroxybenzaldehydazine-, or manganese-supplemented plates but detected no activity, possibly due to a dye-removal mechanism involving reductases. The removal kinetics were studied in liquid medium supplemented with 100 mg L-1 of RB-5 in a selection of 9 yeasts. The highest volumetric-removal rates (η) were found for Candida sake 41E (4.14 mg L-1 h-1), Leucosporidium muscorum F20A (3.90 mg L-1 h-1), and Cystofilobasidium infirmominiatum F13E (3.90 mg L-1 h-1). Different UV-Vis spectra were obtained if the dye removal occurred by biodegradation or biosorption/bioaccumulation. L. muscorum F20A was selected to study the dye-removal mechanism of RB-5 and the effect of different chemical and environmental parameters on the process. Optimum dye-removal conditions were obtained with 10 g L-1 of glucose within an initial medium pH range of 5.0 to 6.0. Up to 700 mg L-1 of dye could be removed in 45 h. High-performance liquid chromatography profiles obtained were consistent with a biodegradation of the dye. Phytotoxicity was estimated by calculating the 50%-inhibition concentration (IC50) with Lactuca sativa L. seeds. These findings propose psychrophilic yeasts as a novel environmentally suitable alternative for the treatment of dye-industry wastewaters.

Production of heterologous polygalacturonase I from Aspergillus kawachii in Saccharomyces cerevisiae in batch and fed-batch cultures.

The pg1 gene from the filamentous fungus Aspergillus kawachii, which codifies for an acid polygalacturonase, was cloned into the pYES2 expression vector, giving rise to the pYES2:pg1ΔI construct. Engineered Saccharomyces cerevisiae, transformed with pYES2:pg1ΔI construct, both expressed and exported an active polygalacturonase with a MW of ~60 kDa and an isoelectric point of 3.7, similar to those reported for the wild-type enzyme. The recombinant enzyme has the ability to hydrolyze polygalacturonic acid at pH 2.5. Heterologous PG1 production was studied under controlled conditions in batch and fed-batch systems. A simultaneous addition of glucose and galactose was found to be the most suitable feeding strategy assayed, resulting in a final PG1 production of 50 U/ml. The production process proposed in this study could be applied for the industrial production of a novel and useful polygalacturonase.

Characterisation of uranium(VI) sorption by two environmental fungal species using gamma spectrometry.

Uranium(VI) sorption by two highly uranium-resistant air-borne fungi in a low-pH medium was measured by means of gamma spectrometry. Growth kinetics and stoichiometry of the two fungal species were also studied. Results show acceptable growth rates in synthetic medium with glucose and ammonia as carbon and nitrogen sources, respectively. Typical oxidative metabolism of carbohydrates was found. In vivo uptake of the radionuclide was negligible, but biosorption dry biomass presented a remarkable performance. The fungal strains showed potential for use in bioremediation.