Ruminal acetogens and their potential to lower ruminant methane emissions

Joblin, K. N.

doi:10.1071/ar99004

Cited by 135 publications

(105 citation statements)

References 41 publications

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“…Creating conditions to support the growth of reductive acetogens is a further strategy for maintaining a low partial pressure of H 2 at the fermentative sites in the rumen digesta (Joblin 1999). However, in the rumen, methanogens usually outcompete acetogens for H 2 .…”

Section: Reductive Acetogenesismentioning

confidence: 99%

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Leng¹

2014

Anim. Prod. Sci.

140

105

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Abstract. Minimising enteric CH 4 emissions from ruminants is a current research priority because CH 4 contributes to global warming. The most effective mitigation strategy is to adjust the animal's diet to complement locally available feed resources so that optimal production is gained from a minimum of animals. This essay concentrates on a second strategy -the use of feed additives that are toxic to methanogens or that redirect H 2 (and electrons) to inhibit enteric CH 4 emissions from individual animals. Much of the published research in this area is contradictory and may be explained when the microbial ecology of the rumen is considered.Rumen microbes mostly exist in organised consortia within biofilms composed of self-secreted extracellular polymeric substances attached to or within feed particles. In these biofilms, individual colonies are positioned to optimise their use of preferred intermediates from an overall process of organic matter fermentation that generates end-products the animal can utilise. Synthesis of CH 4 within biofilms prevents a rise in the partial pressure of H 2 (pH 2 ) to levels that inhibit bacterial dehydrogenases, and so reduce fermentation rate, feed intake and digestibility. In this context, hypotheses are advanced to explain changes in hydrogen disposal from the biofilms in the rumen resulting from use of anti-methanogenic feed additives as follows.Nitrate acts as an alternative electron sink when it is reduced via NO 2 -to NH 3 and CH 4 synthesis is reduced. However, efficiency of CH 4 mitigation is always lower than that predicted and decreases as NO 3 -ingestion increases. Suggested reasons include (1) variable levels of absorption of NO 3 -or NO 2 -from the rumen and (2) increases in H 2 production. One suggestion is that NO 3 -reduction may lower pH 2 at the surface of biofilms, thereby creating an ecological niche for growth of syntrophic bacteria that oxidise propionate and/or butyrate to acetate with release of H 2 .Chlorinated hydrocarbons also inhibit CH 4 synthesis and increase H 2 and formate production by some rumen methanogens. Formate diffuses from the biofilm and is converted to HCO 3 -and H 2 in rumen fluid and is then excreted via the breath. Short-chain nitro-compounds inhibit both CH 4 and formate synthesis when added to ruminal fluid but have little or no effect in redirecting H 2 to other sinks, so the pH 2 within biofilms may increase to levels that support reductive acetogenesis. Biochar or activated charcoal may also alter biofilm activity and reduce net CH 4 synthesis; direct electron transfer between microbes within biofilms may also be involved. A final suggestion is that, during their sessile life stage, protozoa interact with biofilm communities and help maintain pH 2 in the biofilm, supporting methanogenesis.

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Section: Reductive Acetogenesismentioning

confidence: 99%

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Leng¹

2014

Anim. Prod. Sci.

140

105

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“…This suggests that acetogens may serve as hydrogen sinks in experiments, which seek to lower methane emissions (van Nevel and Demeyer, 1995;Morvan et al, 1996;Joblin, 1999) in cattle. Joblin et al (1999) has reported that methane production decreased by 97% and 64%, respectively, when a Methanobrevibacter smithii sp. isolated from a grazing sheep was grown on H 2 /CO 2 in vitro in the presence of a rumen acetogen isolate.…”

Section: Introductionmentioning

confidence: 99%

“…Reductive acetogens are a group of bacteria that can produce acetate from hydrogen and carbon dioxides (4H 2 +2CO 2 →CH 3 COOH+2H 2 O) using the acetyl-CoA pathway (Drake et al, 2006). This suggests that acetogens may serve as hydrogen sinks in experiments, which seek to lower methane emissions (van Nevel and Demeyer, 1995;Morvan et al, 1996;Joblin, 1999) in cattle. Joblin et al (1999) has reported that methane production decreased by 97% and 64%, respectively, when a Methanobrevibacter smithii sp.…”

Section: Introductionmentioning

confidence: 99%

Rumen fermentation and acetogen population changes in response to an exogenous acetogen TWA4 strain and Saccharomyces cerevisiae fermentation product

Yang

Guan

Liu

et al. 2015

J. Zhejiang Univ. Sci. B

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Abstract:The presence of yeast cells could stimulate hydrogen utilization of acetogens and enhance acetogenesis. To understand the roles of acetogens in rumen fermentation, an in vitro rumen fermentation experiment was conducted with addition of acetogen strain (TWA4) and/or Saccharomyces cerevisiae fermentation product (XP). A 2×2 factorial design with two levels of TWA4 (0 or 2×10 7 cells/ml) and XP (0 or 2 g/L) was performed. Volatile fatty acids (VFAs) were increased (P<0.05) in XP and TWA4XP, while methane was increased only in TWA4XP (P<0.05). The increase rate of microorganisms with formyltetrahydrofolate synthetase, especially acetogens, was higher than that of methanogens under all treatments. Lachnospiraceae was predominant in all acetogen communities, but without close acetyl-CoA synthase (ACS) amino acid sequences from cultured isolates. Low-Acetitomaculum ruminis-like ACS was predominant in all acetogen communities, while four unique phylotypes in XP treatment were all amino acid identified low-Eubacterium limosum-like acetogens. It differs to XP treatment that more low-A. ruminis-like and less low-E. limosum-like sequences were identified in TWA4 and TWA4XP treatments. Enhancing acetogenesis by supplementation with an acetogen strain and/or yeast cells may be an approach to mitigate methane, by targeting proper acetogens such as uncultured low-E. limosum-like acetogens.

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“…Effectively, it is wasted feed material and energy that could otherwise be available for animal production. If methanogenesis were reduced in the rumen and the carbon was captured by other mechanisms, such as reductive acetogenesis, this would represent an energetic gain of 4--15% to the animal (Nollet et al 1997;Joblin 1999). Ruminal methane is generated by a diverse group of microorganisms within the Domain Archaea.…”

Section: Introductionmentioning

confidence: 99%

Diversity of methanogens in ruminants in Queensland

Ouwerkerk

Turner

Klieve

2008

Aust. J. Exp. Agric.

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Abstract. Methane emissions from ruminant livestock represent a loss of carbon during feed conversion, which has implications for both animal productivity and the environment because this gas is considered to be one of the more potent forms of greenhouses gases contributing to global warming. Many strategies to reduce emissions are targeting the methanogens that inhabit the rumen, but such an approach can only be successful if it targets all the major groups of ruminant methanogens. Therefore, a thorough knowledge of the diversity of these microbes in different breeds of cattle and sheep, as well as in response to different diets, is required. A study was undertaken using the molecular techniques denaturing gradient gel electrophoresis, DNA cloning and DNA sequence analysis to define the extent of diversity among methanogens in ruminants, particularly Bos indicus cross cattle, on differing forages in Queensland. It was found that the diversity of methanogens in forage-fed cattle in Queensland was greater than in grain-fed cattle but there was little variability in methanogen community composition between cattle fed different forages. The species that dominate the rumen microbial communities of B. indicus cross cattle are from the genus Methanobrevibacter, although rumen-fluid inoculated digestors fed Leucaena leucocephala leaf were populated with Methanosphaera-like strains, with the Methanobrevibacter-like strains displaced. If ruminant methane emissions are to be reduced, then antimethanogen bioactives that target both broad groups of ruminant methanogens are most likely to be needed, and as a part of an integrated suite of approaches that redirect rumen fermentation towards other more useful end products.

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Ruminal acetogens and their potential to lower ruminant methane emissions

Cited by 135 publications

References 41 publications

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation

Rumen fermentation and acetogen population changes in response to an exogenous acetogen TWA4 strain and Saccharomyces cerevisiae fermentation product

Diversity of methanogens in ruminants in Queensland

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