Antibiosis between Ruminal Bacteria and Ruminal Fungi

Abstract

Cellulose digestion, bacterial numbers, and fungal numbers were monitored over time in vitro by using a purified cellulose medium with and without antibiotics (penicillin and streptomycin). All fermentations were inoculated with a 1:10 dilution of whole rumen contents (WRC). Without antibiotics, cellulose digestion was higher (P < 0.01) at 24, 30, 48, and 72 h; fungi had almost disappeared by 24 h, while bacterial concentrations increased over 100-fold in 24 h and then decreased gradually up to 72 h. In those fermentations with added antibiotics, fungal concentrations increased 4-fold by 30 h and up to 42-fold at 72 h; bacterial concentrations were markedly reduced by 24 h and remained low through 72 h. Similar results were obtained with ground alfalfa as a substrate. In further studies, the in vitro fermentation of purified cellulose without antibiotics was stopped after 18 to 20 h, and the microbial population was killed by autoclaving. Antibiotics were added to half of the tubes, and all tubes were reinoculated with WRC. After 72 h, extensive cellulose digestion had occurred in those tubes without antibiotics, as compared to very low cellulose digestion with added antibiotics. The extent of this inhibition was found to increase in proportion to the length of the initial fermentation period, suggesting the production of a heat-stable inhibitory factor or factors. The inhibitory activity was present in rumen fluid, could be extracted from lyophilized rumen fluid (LRF) with water, and was stable in response to proteolytic enzymes. In addition, the water-extracted residue of LRF was found to contain growth factor activity for rumen fungi in vitro.The flagellated microorganisms observed in rumen contents by Liebetanz in 1910 (36) and Braune in 1913 (13) were originally believed to be flagellate protozoa. However, in a series of classic studies, Orpin (39-45) determined that these organisms were actually flagellated zoospores of anaerobic fungi. Although concentrations of the fungi are relatively low in comparison to those of the bacteria and ciliate protozoa, they possess a wide range of enzymes which are capable of hydrolyzing most of the structural polysaccharides occurring in plant cell walls (21,26,35,48,53,55). The fungi also appear to be superior to the rumen bacteria in their ability to break down and degrade the structural barriers in plant material (2). They are able to weaken and partially or fully degrade the more recalcitrant plant tissues as well as penetrate the cuticle barrier (3, 5, 34). When fungi were removed from the rumen, both feed intake and fiber digestibility were decreased; however, total viable bacteria, cellulolytic bacteria, or ciliate protozoal concentrations were not affected (24). Based on in vitro studies with rumen fluid, using antibiotics and a fungicide to selectively culture either the bacteria or fungi, Akin and coworkers (1, 56) concluded that the bacteria were the most active fiberdigesting organisms, even though fungal numbers were increased in the antibiotic-treated cultur...

Effect of balanced supplementary feeding in winter on qualitative and quantitative changes in the population of microbes colonizing the rumen of red deer

“…The cycle of metabolic changes in the rumen has made it possible to identify microbes commonly occurring in it, as well as to determine the ecological interactions taking place between populations (8). The most active ruminal microorganisms are cellulolytic bacteria, mainly of the genera Ruminococcus and Fibrobacter, as well as fungi and protozoa.…”

“…The total number of bacteria in the rumen fluid ranges from 10 9 to 10 12 cells/ml (10,15). Rumen protozoa, which are mainly ciliates, are usually classified on the basis of characteristics of their morphological structure, such as the location of the cilia or the number of skeletal plates (8,10). The number of protozoa in the rumen can reach 10 6 cells/ml and may account for as much as half of the microbial mass in the rumen (15,21).…”

The role of dynamic modelling in understanding the microbial contribution to rumen function

“…A co-culture of two species will become self-regulating and stable if the specific growth rate of the faster-growing species is higher than that of the slower-growing species when [P] is zero. Knowledge on various inhibitory factors produced by micro-organisms in the rumen is limited (Dehority & Tirabasso, 2000). Bacteriocins (antibacterial peptides and proteins characterized by their ability to inhibit strains of bacteria) may have a key role in bacterial population dynamics (Riley, 1998).…”

Production of Cellulolytic Enzymes by Anaerobic Fungi Cultivated in Different Conditions

“…These microorganisms are found regularly distributed in the fluid fraction or adhered to a solid material like the rumen walls. Dehority and Tirabasso (2000) observed that in ruminal content are found flagellate microorganisms that are believed to be flagellate protozoan. On the other hand, a series of studies done by Orpin (1974) established that these microorganisms as flagellate zoospores originating from anaerobic fungi.…”