Financial support: Project INIA-LIA 057, CSIC 308 and by the Maestría en Biotecnología, Facultad de Ciencias, Universidad de la República, Uruguay.

Keywords: agroindustry, basidiomycetes, ruminant feed.

The increasing expansion of agro-industrial activity has led to the accumulation of a large quantity of lignocellulosic residues all over the world. In particular, large quantities of rice straw (300.000 t) and citric bagasse (50.000 t) are annually produced in Uruguay. In this work we present the study of the bioconversion of these substrates with the edible mushroom Pleurotus spp so as to increase nutritional values and digestibility for its use as animal feed. The SSF process was optimized and the products after different periods of mushroom growth were evaluated. The microbial counts (cfu/g) for the inoculated substrates 44 days after incubation were 15 x 10⁴, < 10 and < 10 for aerobic microorganisms, coliforms and E. coli, respectively. After 14 days of SSF the percentage of dry matter, ADF and NDF decreased, and the content of protein increased. These results show that vegetal cell-wall components were degraded during the period of mushroom incubation. PCR – RFLP analysis of the ITS region was used to characterize the Pleurotus species produced in Uruguay and discriminate between DNAs of Pleurotus ostreatus 814 and other fungi from the different substrates.