Poster apresentado no XIII Congresso Nacional de Bioquímica, Lisboa, 5-7 Dezembro 2002.An ascomycete yeast strain, UM41 , was isolated from a textile wastewater treatment facility, and selected on the basis of its azo dye decolourising activity. Growing yeast cultures in liquid media containing glucose and 0.2mM dye removed more than 80% of the colour in 15 h, and total decolourisation of the tested dyes occured in 24 h. Colour loss is due to a constitutive azoreductase activity, expressed in intact cells, but not detectable in supernatant samples or cell-free extracts. This activity suffers thermal inactivation at temperatures higher than 50ºC and its dependence on dye concentration is satisfactorily described by the Michaelis-Menten model. Specific decolourising activities of resting cells have a maximum during the late exponential growth phase and are enhanced by up to 3-fold by the redox mediator AQS. The effect of pH on the decolourisation rates is structure-dependent. UM41 growing on glucose-containing medium initially exhibits a predominantly fermentative metabolism and produces ethanol, while oxygen is quicky depleted from the culture medium. However the same batch of cells retained decolourising activity for up to five successive cycles of dye removal, without any further nutrient addition. The microorganism growth and dye decolourisation observed after glucose exhaustion probably occur at the expense of ethanol, suggesting that decoulorisation is also compatible with a respiratory metabolism.BIOEFTEX
