G. Fonty

Quantitative Determination of H2-Utilizing Acetogenic and Sulfate-Reducing Bacteria and Methanogenic Archaea from Digestive Tract of Different Mammals

Abstract. Total number of bacteria, cellulolytic bacteria, and H2-utilizing microbial populations (methanogenic archaea, acetogenic and sulfate-reducing bacteria) were enumerated in fresh rumen samples from sheep, cattle, buffaloes, deer, llamas, and caecal samples from horses. Methanogens and sulfate reducers were found in all samples, whereas acetogens were not detected in some samples of each animal. Archaea methanogens were the largest H2-utilizing populations in all animals, and a correlation was observed between the numbers of methanogens and those of cellulolytic microorganisms. Higher counts of acetogens were found in horses and llamas (1 × 104 and 4 × 104 cells ml−1 respectively).

Effects of glycerol on the growth, adhesion, and cellulolytic activity of rumen cellulolytic bacteria and anaerobic fungi.

The effect of glycerol on the growth, adhesion, and cellulolytic activity of two rumen cellulolytic bacterial species,Ruminococcus flavefaciens andFibrobacter succinogenes subsp.succinogenes, and of an anaerobic fungal species,Neocallimastix frontalis, was studied. At low concentrations (0.1–1%), glycerol had no effect on the growth, adhesion, and cellulolytic activity of the two bacterial species. However, at a concentration of 5%, it greatly inhibited their growth and cellulolytic activity. Glycerol did not affect the adhesion of bacteria to cellulose. The growth and cellulolytic activity ofN. frontalis were inhibited by glycerol, increasingly so at higher concentrations. At a concentration of 5%, glycerol totally inhibited the cellulolytic activity of the fungus. Thus, glycerol can be added to animal feed at low concentrations.

Effects of live Saccharomyces cerevisiae cells on zoospore germination, growth, and cellulolytic activity of the rumen anaerobic fungus, Neocallimastix frontalis MCH3.

The effects of a live yeast strain of Saccharomyces cerevisiae have been investigated on zoospore germination, metabolism, and cellulolytic activity of the anaerobic rumen fungus Neocallimastix frontalis MCH3. The addition of yeast cells to a vitamin-deficient medium stimulated the germination of fungal zoospores, increased cellulose degradation and hydrogen, formate, lactate, and acetate production. Responses depended on the concentration of yeast cells added and on their viability. Yeast supplementation provided vitamins such as thiamine, which is essential for fungal growth and activity. These results demonstrate that yeasts could enhance plant cell wall colonization by N. frontalis. With certain diets, yeasts could therefore be a good tool to optimize the microbial degradation of lignocellulosic materials, but more research is needed to understand their mechanisms of action, so that they can be used with maximum efficiency as feed supplements.

Rumen anaerobic fungi and plant substrate colonization as affected by diet composition

Abstract The influence of diet composition on rumen fungal population was studied by offering successively to a rumen fistulated cow 11 different diets rich in fibre, starch or soluble carbohydrates. At the same time, the colonization of four different plant substrates introduced into the rumen in nylon bags (soya bean teguments, lucerne stems, maize stalks and beet pulps) was investigated. The population of rumen anaerobic fungi, particularly abundant with lignocellulose-rich diets, decreased with starch or soluble-carbohydrate-rich diets; the fungi selectively colonized the plant tissues with thick or lignified cell walls of soya bean tegument, lucerne or maize stalks, but seldom the beet pulp. The development of rumen fungi depended both on the substrate on which they became attached and on the ruminal medium. The fungi, which were normally present in the duodenum, caecum and faeces, were eliminated by the unfavourable diet but rapidly proliferated once the feed ingredients became more favourable.

Isolation and characterization of cultivable fermentative bacteria from the intestine of two edible snails, Helixpomatia and Cornu aspersum (Gastropoda: Pulmonata)

The intestinal microbiota of the edible snails Cornu aspersum fSyn: H. aspersa), and Helix pomatia were investigated by culture-based methods, 16S rRNA sequence analyses and phenotypic characterisations. The study was carried out on aestivating snails and two populations of H. pomatia were considered. The cultivable bacteria dominated in the distal part of the intestine, with up to 5.10(9) CFU g -1, but the Swedish H. pomatia appeared significantly less colonised, suggesting a higher sensitivity of its microbiota to climatic change. All the strains, but one, shared >/= 97% sequence identity with reference strains. They were arranged into two taxa: the Gamma Proteobacteria with Buttiauxella, Citrobacter, Enterobacter, Kluyvera, Obesumbacterium, Raoultella and the Firmicutes with Enterococcus, Lactococcus, and Clostridium. According to the literature, these genera are mostly assigned to enteric environments or to phyllosphere, data in favour of culturing snails in contact with soil and plants. None of the strains were able to digest filter paper, Avicel cellulose or carboxymethyl cellulose (CMC). Acetogens and methanogenic archaea were not cultivated, so the fate of hydrogen remains questionable. This microbiota could play important roles in the digestive process (fermentation) and the energy supply of the snail (L-lactate, acetate). The choice of cereals and plants by snail farmers should take into account the fermentative abilities of the intestinal microbiota.

Degradation and fermentation of cellulose by the rumen anaerobic fungi in axenic cultures or in association with cellulolytic bacteria

Three rumen anaerobic fungi—Neocallinastix frontalis MCH3,Piromyces (Piromonas) communis FL, andCaecomyces (Sphaeromonas) communis FG10—were cultured on cellulose filter paper alone or in association with one of two rumen cellulolytic bacteria,Ruminococcus flavefaciens 007 andFibrobacter succinogenes S85. Cocultures ofN. frontalis orP. communis andR. flavefaciens were markedly less effective than the fungal monocultures in degrading cellulose but more effective than the bacterial monocultures.R. flavefaciens had an antagonistic effect against both of the fungal species. In contrast, no interaction was observed between the two fungal species andF. succinogenes. Cellulose was more effectively degraded by the cocultureC. communis-R. flavefaciens than by the corresponding fungal and bacterial monocultures. The effectiveness of degradation of the cocultureC. communis-F. succinogenes was comparable to that of the bacterial strains but greater than that of the fungi; no interaction was observed between these two microorganisms.

Ecological Factors Determining Establishment of Cellulolytic Bacteria and Protozoa in the Rumens of Meroxenic Lambs

Ecological factors that control the establishment of cellulolytic bacteria and ciliate protozoa in the lamb rumen were studied in meroxenic animals. Axenic lambs received dilutions of rumen liquor from either conventional lambs and sheep (pool A) or meroxenic lambs (pool B). The total number of bacteria established in the rumen was between 10(9) and 5 x 10(10) g-1. In lambs inoculated with dilutions (10(-6), 10(-7), 10(-8)) of pool A, cellulolytic bacteria did not become established. However, subsequent inoculation with Bacteroides succinogenes, resulted in colonization in lambs that had received 10(-6) and 10(-7) dilutions of pool A. However, B. succinogenes became established in only one of three lambs that received the 10(-8) dilution. Similar results were obtained for the protozoan Entodinium sp. With pool B, lambs were inoculated earlier and cellulolytic bacteria were established directly from the 10(-6) and 10(-7) inocula. Polyplastron multivesiculatum establishment occurred readily when inoculated into the lambs which had received the 10(-6) dilution of pool B. Results obtained in this study suggest that establishment of cellulolytic bacteria and protozoa requires an abundant and complex flora and is favoured by early animal inoculation.

Postprandial variations in the activity of polysaccharide-degrading enzymes of fluid- and particle-associated ruminal microbial populations

The distribution and specific activities of polysaccharide-degrading enzymes were monitored during the postprandial period in the liquid-associated bacteria (LAB), liquid-associated protozoa (LAP), and solid-associated microbes (SBFP) isolated from ruminal contents of cattle fed a high-cereal diet. Polysaccharide depolymerase activities were highest in the SBFP and the LAP populations. The postprandial variations in the specific activity of amylase were similar within the subpopulations. However, carboxymethylcellulase and xylanase activities increased in the first 5 h after feeding in the LAP, but were highest at the end of the postprandial period in the SBFP. Glycosidases involved in the fermentation of soluble carbohydrates increased significantly immediately after feeding in the liquid-associated microbes. β-d-Glucosidase and β-d-xylosidase were most active in the SBFP and were maximal 23 h after feeding. The activities of the plant cell wall polysaccharide-degrading enzymes and glycosidases in the SBFP were inversely related to ruminal pH; however, the activity of enzymes in the liquid-associated populations were highest in the immediate post-feed period when ruminal pH was lowest.

Establishment, counts, and identification of the fibrolytic microflora in the digestive tract of rabbit. Influence of feed cellulose content

In the young rabbit, the celluloytic population appeared in the cecum and colon microflora between 12 and 16 days after birth. It increased rapidly with age to stabilize at a level of about 107 bacteria a few days after weaning. In the adult animal the xylanolytic and pectinolytic populations established at levels between 109 and 1010 bacteria g−1. The colic and cecal populations were comparable in size. When the feed cellulose content rose from 11 to 17% (P/V), the cellulolytic population increased about tenfold, and the range of individual variations decreased. All the fibrolytic strains isolated were strictly anaerobic;Eubacterium cellulosolvens was the most frequently isolated cellulolytic species. The eight xylanolytic strains and the twelve pectinolytic strains identified were assigned to the speciesBacteroides ruminicola.

Competition Between Ruminal Cellulolytic Bacteria for Adhesion to Cellulose

Abstract. Competition for adhesion to cellulose among the three main ruminal cellulolytic bacterial species was studied using differential radiolabeling (14C/3H) of cells. When added simultaneously to cellulose, Ruminococcus flavefaciens FD1 and Fibrobacter succinogenes S85 showed some competition; however, both species were surpassed competitively by Ruminococcus albus 20. When R. flavefaciens FD1 and F. succinogenes S85 were already adherent, R. albus 20 adhesion occurred without inhibition but involved R. flavefaciens FD1 detachment.