Rumen bacterial and fungal degradation of Digitaria pentzii grown with or without sulfur

Abstract

Sheep fed the forage Digitaria pentzii fertilized with sulfur were compared with those fed unfertilized forage for the rumen microbial population involved with fiber degradation. No differences were detected in the bacterial population as determined by anaerobic cultures on a habitat-simulating medium, xylan, or pectin, by 35S labeling techniques for microbial protein, or by transmission electron microscopic studies of bacterium-fiber interactions. Rumen volume and water flow from the rumen were not different for sheep fed each of the forages. Rumen fungi were prevalent in sheep fed sulfur-fertilized D. pentzii as shown by sporangia adhering to forage fiber and by colonies developing from zoospores in roll tubes with cellobiose plus streptomycin and penicillin. Fungi were absent or in extremely small numbers in sheep fed unfertilized forage. Nylon bag digestibility studies showed that the fungi preferentially colonized the lignified cells of blade sclerenchyma by 6 h and caused extensive degradation by 24 h. In the absence of bacteria in in vitro studies, extensive hyphal development occurred; other lignified tissues in blades (i.e., mestome sheath and xylem) were attacked, resulting in a residue with partially degraded and weakened cell walls. Nonlignified tissues were also degraded. Breaking force tests of leaf blades incubated in vitro with penicillin and streptomycin and rumen fluid from sheep fed sulfurfertilized forage or within nylon bags in such sheep showed a residue at least twice as fragile as that from sheep fed unfertilized forage. In vitro tests for dry matter loss showed that rumen fungi, in the absence of actively growing bacteria, could remove about 62% of the forage material. The response of rumen fungi in sheep fed sulfur-fertilized D. pentzii afforded a useful in vivo test to study the role of these microbes in fiber degradation. Our data establish that rumen fungi can be significant degraders of fiber and further establish a unique role for them in attacking and weakening lignocellulosic tissues. The more fragile residues resulting from attack by fungi could explain the greater intake consistently observed by sheep eating sulfur-fertilized compared with unfertilized D. pentzii forage. Rees and co-workers (32, 33) showed that sulfur fertilization (+S) reduced retention time of forage in the rumen and increased voluntary intake and digestibility compared with unfertilized (-S) Digitaria sp. forage. The authors suggested that depressed microbial activity due to a sulfur deficiency could have caused poor animal response to-S forage. Similar studies with +S and-S Digitaria pentzii (31) indicated that S fertilization increased voluntary intake and reduced rumen ammonia levels, indicating enhanced microbial activity in the rumen.

The Cellulase/Hemicellulase System of the Anaerobic FungusOrpinomycesPC‐2 and Aspects of Its Applied Use

“…36 They are responsible for most of the plant cell wall degradation in the rumen ecosystem, where they seem to interact with rumen bacteria. 19,45,100 As pointed out above, individual enzymes from anaerobic fungi isolated or obtained by cloning generally have higher specific activities than similar enzymes from other sources. These properties seem to be of value when considering enzymes from anaerobic fungi for industrial uses, which may involve the bioconversion of lignocellulose to sugars fermentable to ethanol for fuel or the production of other industrial feed stock chemicals.…”

“…In addition, accessory enzymes were found for hemicellulose degradation, including acetyl xylan esterase, feruloyl-and p-coumaroyl esterases, and α-(4-O-methyl)-glucoronidase. 19,20 Two feruloyl esterases (FAE-I and FAE-II), and one p-coumaroyl esterase (CAE) have been purified from culture media of Neocallimastix strain MC-2. 78,79 These esterases function synergetically together with commercial xylanase preparations from Trichoderma viride (Sigma-Aldrich Corp., St. Louis, MO) and Basidiomycetes (Driselase; Sigma).…”

“…It has been suggested that, in herbivorous animals, anaerobic fungi are the initial colonizers of lignocellulose and play an essential role in fiber digestion. [17][18][19] They ferment the sugars, yielding formate, acetate, ethanol, lactate, CO 2, and H 2 as the main end products. 20,21 Knowledge about anaerobic fungi is rapidly accumulating, especially pertaining to their ability to produce plant hydrolyzing enzymes, including cellulases, β-glucosidases, xylanases, βglucanases/lichenases, mannanases, cinnamoyl esterases/feruloyl-and p-coumaroyl esterases, acetyl xylan esterase, and (4-0-methyl)-D-glucuronidase/ α-glucuronidase.…”

Two genes of the anaerobic fungus Orpinomyces sp. strain PC-2 encoding cellulases with endoglucanase activities may have arisen by gene duplication

“…Since the ¢rst anaerobic fungus, Neocallimastix frontalis, was isolated in 1975 from the rumen of sheep [1], at least 17 di¡erent anaerobic fungi have been isolated from ruminant and nonruminant herbivores. Anaerobic fungi produce highly active hydrolytic enzymes [2], they physically associate with the lignocellulosic tissue of plant fragments, and their hyphae penetrate the plant tissue in vivo [3,4], indicating that they are involved in degradation of plant biomass and play an important role in the rumen ecosystem. Several genes coding for hydrolytic enzymes have been cloned and sequenced from the monocentric fungi Neocallimastix patriciarum [5^9], N. frontalis [10,11], and Piromyces sp.…”

Proteolytic activity of a rumen anaerobic fungus

“…Since Orpin [1,2] found that several flagellated protozoa in the rumen were in fact the zoospore stages of strictly anaerobic phycomycetous fungi, studies have been directed towards establishing the importance of these fungi in the rumen. Light and electron microscopy have shown that the fungi are attached to plant material [3][4][5] and it has been suggested that they play a role in degrading [5] and weakening plant fibre [6].…”