In the present work, a yeast strain Pichia kudriavzevii was identified on the basis of 18S rDNA, showing maximum growth at 30°C and pH 7.0. Among all the complex polysaccharides used, wheat bran proved to be the best substrate as indicated by the maximum growth of the yeast strain. The yeast isolate was capable of producing xylanase both intra-and extra-cellularly, the dominant form being extracellular. The maximum enzyme activity was determined at pH 5.0 and at 50°C. Na+, Mg2+ and Fe2+ presence caused a substantial increase in enzyme activity while a slight decrease (4.5%) was observed in the presence of Mn2+, Zn2+ and Cu2+. Pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activities were assayed to confirm the presence of the ethanol pathway and PDC activity was much more pronounced (73%) compared to ADH activity (51%). The yeast strain can be employed to utilize hemicellulose containing agroindustrial residues for ethanol production.

En el presente estudio se identificó en aguas residuales de una zona industrial de Pakistán una cepa de la levadura Pichia kudriavzevii sobre la base del 18S ADNr, dicha cepa mostró un crecimiento máximo a 30 °C y a pH 7. Entre todos los sustratos de crecimiento evaluados para esta cepa, que incluyeron residuos industriales y medios definidos, el salvado de trigo demostró ser el mejor en función del crecimiento máximo alcanzado. Este aislado de levadura fue capaz de producir xilanasa intracelular y extracelular, esta última fue la forma predominante. Dicha capacidad enzimàtica mostró ser óptima a un pH de 5 y a 50°C. La presencia de Na+, Mg2+ y Fe2+ causó un incremento sustancial de la actividad enzimática, y hubo un ligero descenso (4,5%) en presencia de Mn2+, Zn2+ y Cu2+. Se evaluaron también las actividades de piruvato descarboxilasa y alcohol deshidrogenasa para confirmar la presencia de la vía del etanol. La actividad de la piruvato descarboxilasa fue mucho más pronunciada (73%) en comparación con la de alcohol deshidrogenasa (51%). Esta cepa de levadura puede emplearse para aprovechar los materiales hemicelulósicos de los residuos agroindustriales en la producción de etanol.

ABSTRACT Trichosporon asahii and Rhodotorula mucilaginosa isolated from wastewater effluents were identified as chromium-resistant yeasts. Cr(VI) concentrations at 8 mM and 6 mM were inhibitory for R. mucilaginosa and T. asahii. Remarkably elevated GSH (69.88 ± 10.01) and GSSG (11.24 ± 0.96) was observed under metal stress in T. asahii as compared to R. mucilaginosa GSH (18.95 ± 3.19) and GSSG (3.7 ± 2.74) mM g-1 8 level. Statistical analysis revealed significantly higher GSH/GSSG ratio in both strains. NPSH (29.84 ± 0.54) level in T. asahii was much higher than in R. mucilaginosa (6.05 ± 0.24). Chromate reductase (ChR) was assayed and its activity was optimum at 50°C (pH 6) in T. asahii while R. mucilaginosa showed higher activity at 30°C (pH 7). Activity of both ChRs was enhanced in the presence of Mg, Na, Co and Ca but strongly inhibited by Hg cations. Cr(VI) uptake capabilities were ranged between 43-97% in R. mucilaginosa and 35-88% in T. asahii. One dimensional electrophoresis revealed enriched bands of cysteine rich metallothioneins suggesting some differential proteins could be overexpressed under Cr(VI) stress.