Detection of Proteobacteria from the rumen by PCR using methanotroph-specific primers

Meunier

et al. 2007

Bacteria attached to the rumen epithelium (or epimural community) are not well characterised and their role in rumen functioning is not totally understood. There is just one published report of a clone library from one cow that suggests that this epimural community differs from the bacteria associated with the rumen digestive contents. However, this time-consuming approach is not adapted for examining microbial population changes in groups of animals. In in vivo studies, when samples from several animals have to be analysed simultaneously, a simpler technique has to be used. In this study, a genetic fingerprinting technique, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), was used to characterise the structure of the bacterial population attached to the rumen epithelium. This community was compared with that present in the solid and liquid phases of rumen content under two contrasting diets. Rumen samples were obtained from four forage-fed and four high-concentrate-fed (80 : 20, wheat grain : hay) 5-month-old lambs. After slaughter, samples from five epithelial sites and the solid and liquid digesta phases were taken for DNA extraction and analysis. Bacterial communities were profiled by PCR-DGGE using bacterial-specific 16S rDNA primers. Analysis of the fingerprint revealed that the epithelial community differed from those of rumen content in both diets. As expected, the nature of the feed influenced the bacterial communities from the solid and liquid rumen phases but no diet effect was observed in the rumen epithelial profiles suggesting a strong host effect on this bacterial population. Additionally, no differences were observed among the five epithelial sampling sites taken from each animal. The profile of the bacterial population attached to the rumen epithelium presented a high interanimal variation, whether this difference has an influence in the function of this community remains to be determined.

Section: Discussionmentioning

confidence: 65%

PCR-DGGE analysis reveals a distinct diversity in the bacterial population attached to the rumen epithelium

Sadet

Meunier

et al. 2007

“…This oxidation was found to be anaerobic and associated with sulphate reduction. In contrast, putative methane-oxidising bacteria, evidenced by PCR amplification with specific primers, were found attached to the rumen epithelium (Mitsumori et al, 2002) where conditions may favour aerobic oxidation of methane. This metabolic pathway has yet to be quantified in vivo.…”

Section: Bacteria Using Alternative H 2 Sinksmentioning

confidence: 90%

Microbial ecosystem and methanogenesis in ruminants

Morgavi

Forano²,

et al. 2010

525

406

Ruminant production is under increased public scrutiny in terms of the importance of cattle and other ruminants as major producers of the greenhouse gas methane. Methanogenesis is performed by methanogenic archaea, a specialised group of microbes present in several anaerobic environments including the rumen. In the rumen, methanogens utilise predominantly H 2 and CO 2 as substrates to produce methane, filling an important functional niche in the ecosystem. However, in addition to methanogens, other microbes also have an influence on methane production either because they are involved in hydrogen (H 2 ) metabolism or because they affect the numbers of methanogens or other members of the microbiota. This study explores the relationship between some of these microbes and methanogenesis and highlights some functional groups that could play a role in decreasing methane emissions. Dihydrogen ('H 2 ' from this point on) is the key element that drives methane production in the rumen. Among H 2 producers, protozoa have a prominent position, which is strengthened by their close physical association with methanogens, which favours H 2 transfer from one to the other. A strong positive interaction was found between protozoal numbers and methane emissions, and because this group is possibly not essential for rumen function, protozoa might be a target for methane mitigation. An important function that is associated with production of H 2 is the degradation of fibrous plant material. However, not all members of the rumen fibrolytic community produce H 2 . Increasing the proportion of non-H 2 producing fibrolytic microorganisms might decrease methane production without affecting forage degradability. Alternative pathways that use electron acceptors other than CO 2 to oxidise H 2 also exist in the rumen. Bacteria with this type of metabolism normally occupy a distinct ecological niche and are not dominant members of the microbiota; however, their numbers can increase if the right potential electron acceptor is present in the diet. Nitrate is an alternative electron sinks that can promote the growth of particular bacteria able to compete with methanogens. Because of the toxicity of the intermediate product, nitrite, the use of nitrate has not been fully explored, but in adapted animals, nitrite does not accumulate and nitrate supplementation may be an alternative under some dietary conditions that deserves to be further studied. In conclusion, methanogens in the rumen co-exist with other microbes, which have contrasting activities. A better understanding of these populations and the pathways that compete with methanogenesis may provide novel targets for emissions abatement in ruminant production.

“…In another study bacterial clones closely related to Nitrosomonas spp. were identified from a clone library constructed from samples of bacterial communities attached to the rumen epithelium (Mitsumori et al, 2002). Members of the genus Nitrosomonas are ammoniaoxidising bacteria, which have the ability to oxidise CH 4 under some conditions (Hyman and Wood, 1983;Jiang and Bakken, 1999).…”

Section: Methylotrophsmentioning

confidence: 99%

The use of direct-fed microbials for mitigation of ruminant methane emissions: a review

Jeyanathan

Morgavi

2014

123

115

Concerns about the environmental effect and the economic burden of methane (CH 4 ) emissions from ruminants are driving the search for ways to mitigate rumen methanogenesis. The use of direct-fed microbials (DFM) is one possible option to decrease CH 4 emission from ruminants. Direct-fed microbials are already used in ruminants mainly to increase productivity and to improve health, and are readily accepted by producers and consumers alike. However, studies on the use of DFM as rumen CH 4 mitigants are scarce. A few studies using Saccharomyces cerevisiae have shown a CH 4 -decreasing effect but, to date, there has not been a systematic exploration of DFM as modulators of rumen methanogenesis. In this review, we explored biochemical pathways competing with methanogenesis that, potentially, could be modulated by the use of DFM. Pathways involving the redirection of H 2 away from methanogenesis and pathways producing less H 2 during feed fermentation are the preferred options. Propionate formation is an example of the latter option that in addition to decrease CH 4 formation increases the retention of energy from the diet. Homoacetogenesis is a pathway using H 2 to produce acetate, however up to now no acetogen has been shown to efficiently compete with methanogens in the rumen. Nitrate and sulphate reduction are pathways competing with methanogenesis, but the availability of these substances in the rumen is limited. Although there were studies using nitrate and sulphate as chemical additives, use of DFM for improving these processes and decrease the accumulation of toxic metabolites needs to be explored more. There are some other pathways such as methanotrophy and capnophily or modes of action such as inhibition of methanogens that theoretically could be provided by DFM and affect methanogenesis. We conclude that DFM is a promising alternative for rumen methane mitigation that should be further explored for their practical usage.