Abstract
Fungi have the ability to degrade vegetal cell wall carbohydrates, and their presence in the digestive tract of ruminants can minimize the effects of lignified forage on ruminal fermentation. Here, we evaluated enzyme production by Aspergillus spp. isolates from the digestive tracts of cattle grazed in tropical pastures during the dry season. Filamentous fungi were isolated from rumen and feces by culture in cellulose-based medium. Ninety fungal strains were isolated and identified by rDNA sequence analysis, microculture, or both. Aspergillus terreus was the most frequently isolated species, followed by Aspergillus fumigatus. The isolates were characterized with respect to their cellulolytic, xylanolytic, and lignolytic activity through qualitative evaluation in culture medium containing a specific corresponding carbon source. Carboxymethyl cellulase (CMCase) activity was quantified by the reducing sugar method. In the avicel and xilan degradation test, the enzyme activity (EA) at 48 h was significantly higher other periods (P < 0.05). Intra- and inter-specific differences in EA were verified, and high levels of phenoloxidases, which are crucial for lignin degradation, were observed in 28.9% of the isolates. Aspergillus terreus showed significantly higher EA for avicelase (3.96 ±1.77) and xylanase (3.13 ±.091) than the other Aspergillus species at 48 h of incubation. Isolates AT13 and AF69 showed the highest CMCase specific activity (54.84 and 33.03 U mg-1 protein, respectively). Selected Aspergillus spp. isolates produced remarkable levels of enzymes involved in vegetal cell wall degradation, suggesting their potential as antimicrobial additives or probiotics in ruminant diets.
Highlights
Fibrous vegetation is the basis of the ruminant diet, and degradation of the cell wall carbohydrates in plant fibers is fundamental to ruminant digestion [1]
We evaluated the enzyme activity (EA) of Aspergillus spp. isolates from the digestive tract of cattle grazing on lignified tropical pasture to select strains with the optimal ability to degrade plant cell walls
We evaluated the correlation between the EA indices for xylan and cellulose by Spearman correlation
Summary
Samples were collected from Nellore (Zebu) beef cattle on farms in Montes Claros and Coracão de Jesus in northern Minas Gerais State, Brazil. This region is located at approximately 16 ̊ 51’ S and 44 ̊ 55’ W, and it has a humid tropical climate with a dry summer (As), according to the Koppen classification [15], marked by a dry season from May to September and a rainy season from December to February. After eight hours of fasting, calves were immobilized in a restraint chute to obtain rumen fluid using a sterile catheter as described by Abrão et al [10]. Fecal samples were obtained directly from the rectal ampulla with a sterile
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