Seleção de leveduras para bioconversão de D-xilose em xilitol / Yeast selection for bioconversion of D-xylose to xilitol

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

Microbial species, particularly yeast, are of great importance for the production of xylitol. The xylitol production involves complicated metabolic regulation, including the transport of D-xylose, production of key enzymes and cofactor regeneration. Thus, screening of microorganisms that consume D-xylose naturally becomes a viable and effective way to obtain organisms with industrial application for the production of xylitol. In this work we isolated twenty-eight yeasts from the environment of the industrial production of ethanol (filter cake) with capacity to consume D-xylose. The sequencing and identification by analysis of the D1/D2 region of 26S rDNA gene showed that all belong to the genus Candida, and 24 strains (85.71%) C. tropicalis and 4 strains (14.29%) C. rugosa. Of the 28 isolates, five strains of yeast were selected randomly to test the bioconversion of D-xylose to xylitol due to the fact that they present rate of growth in D-xylose similar. The lines selected for testing were: Candida tropicalis MVP 03, Candida tropicalis MVP 16, Candida rugosa MVP 17, Candida rugosa MVP 21, Candida tropicalis MVP 40, and they represent a sampling. Three yeasts from the collection of the Department of Biological Sciences, ESALQ / USP (Kluyveromyces marxianus IZ 1339, Candida tropicalis IZ 1824 and Candida guilliermondii FTI 20037), used were the tests to obtain xylitol from the bioconversion of D-xylose as positive control, for the formation of xylitol in a synthetic medium using D-xylose as sole carbon source. Assays were performed in the kinetics of growth during 96 hours of fermentation. In the first evaluation, the evaluation of the best nutritional condition in the test, yeast cells were grown in three chemically defined media: YNB 6.7 g L-1, UPX (urea 2.3 g L-1 peptone and 6.6 g L-1) MCX ( KH2PO4 0.62 g L-1, K2HPO4 2.0 g L-1, (NH4)2SO4 1.0 g L-1 MgSO4 1.1 g L-1, yeast extract 0.5 g L-1) plus 20 g L-1 D-xylose at 30°C and 120 rpm. Mean UPX showed the best performance with a volumetric productivity (Qp) from 0.004 to 0.09, the conversion factor of xylose to xylitol (Yp/s) between 0,23 to 0,28 g g-1 conversion factor D-xylose in biomass (Yx/s) between 0.20 to 0.24 g g-1 Yeasts 0,20 to 0,24 g g-1, with a conversion efficiency (h) between 21% to 26%. C. tropicalis MVP 03, C. tropicalis MVP 16, C. rugosa MVP 17, C. rugosa MVP 21, C. tropicalis MVP 40 were evaluated in a screening, in media UPX, with standardization of initial inoculation. For 12 five isolates, the production of xylitol varied from 5.76 to 32.97 g L-1, from 50 g L-1 Dxylose with productivity (Qp) of 0.06 to 0,35 g L-1 h-1, the conversion factor of xylose to xylitol (Yp/s) 0.14 to 0.65 g g-1, the conversion factor of D-xylose in biomass (Yx/s) from 0.08 to 0.29 g g-1 and conversion efficiency (h) between 6% and 61% which was calculated according to Barbosa et al 1988. They outlined the yeast C. tropicalis MVP16, yielding 32.97 g L-1 of xylitol with a Qp of 0.35 g L-1 h-1, Yp/s to 0.65 g g-1, Y x/s of 0.11 g g -1 and conversion efficiency (h) of 61%.

ASSUNTO(S)

dna sequence. candida yeast-isolation and purification aerobic fermentation leveduras - isolamento e purificação candida sequência do dna fermentação aeróbica

ACESSO AO ARTIGO

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