Resumo

The biotechnology potential of fungal in the enzyme production is widely studied. In ruminant nutrition the addition of Aspergillus oryzae or other fungi has favored the degradation and utilization of forage. However, little is known about the population of aerobic fungi naturally found in the rumen fluid. The objective was to evaluate the cellulolytic activity of aerobic mycelian fungi from digestive tract of dairy cattle fed with tropical forages. Isolates of fungi were obtained from 30 samples of rumen fluid from cows fed with sorghum silage, 32 cows fed on Brachiaria brizantha, 12 heifers receiving sorghum silage and 11 heifers fed with cane sugar. The isolation was performed on C solid medium containing cellulose. Were evaluated 49 isolates, 27 Aspergillus spp., four Gliocladium spp., six Paecilomyces spp., nine Rhizophus spp. and three of the genus Scedosporium. These isolates were incubated in C medium with 1% microcrystalline cellulose as the sole carbon source, and incubated at 37°C in triplicate. Cellulolytic activity indices were verified after 24, 48 and 72 hours and calculated by the ratio between the degradation halo, observed with congo red, and the colony diameter for comparing in Krusskal-Wallis tests. In culture with C medium was found significantly lower positivity rate (86.7%) for cows fed only on B. brizantha pasture than observed for cows fed with sorghum (100% of positivity rate, p<0.05 in chi-square test). The genus Aspergillus showed higher cellulolytic activity index mean than isolates of Rhizophus genus (p<0.05). Eight isolates of Aspergillus spp. and six of Paecilomyces spp. showed this index higher than one, Especially the V841 isolate of the Aspergillus terreus species from the rumen of a cow fed on pasture corresponded the fungi with the highest cellulolytic activity (2,366) with 48 hours of culture. The selected isolates show potential for cellulase production and utilization in ruminant nutrition as microbial additives or probiotics or for microbial industry.