The discovery that a bacterial species in the Australian Tammar wallaby
gut is responsible for keeping the animal’s methane emissions
relatively low suggests a potential new strategy may exist to try to
reduce methane emissions from livestock, according to a new study.
livestock are the largest source of methane from human-related
activities, and are the third-largest source of this greenhouse gas in
the United States, according to the U.S. Environmental Protection
and other marsupials are dependent on microbes to support their
digestive system, similar to livestock such as cows, sheep, and goats,
but Tammar wallabies are known to release about 80% less methane
gas per unit of digestible energy intake than do livestock animals.
have used DNA sequence data to devise a way to isolate and grow
cultures of a dominant bacterial species from the Tammar wallaby gut and
test its characteristics. The analysis confirmed that this bacterium
would contribute to a digestion process that produces low levels of
methane. Using this information, scientists hope to devise a way to
augment the microbial mix in livestock animals’ digestive systems and
therefore reduce their methane emissions.
added bonus for the wallabies, the researchers say, is that the
presence of this bacterium frees up more digestible energy for
nutritional purposes in host animals. The energy the fermentation
process uses to produce methane gas during digestion actually robs
animals of some of the nutritional quality of their food.
long-term goals are really to improve nutrient retention by livestock,
and reducing methane emissions is just one area where we seek to have a
positive impact, both on animal productivity and the environment,” said
Mark Morrison, senior author of the study and a professor of animal
sciences at Ohio State University. Morrison is also the science leader
in metagenomics for CSIRO (Commonwealth Scientific & Industrial
Research Organization) Division of Livestock Industries based in
The study is in Science and appears online as a Science Express report.
are often considered similar to ruminants—a class of mammals that
have multiple compartments, including one called a rumen, in their
stomachs—because both groups have a digestive system that supports a “predigestion” of food by microbes, to process their plant-based diets.
And this process, which includes a period of fermentation to break down
the foods and release nutrients, causes the animals to discharge
methane gas. Over time, however, researchers have noted that Tammar
wallabies in particular produce only about a fifth of the amount of
methane produced by livestock ruminants as a result of differences in
anatomy and microbial compositions in their guts.
research in this area showed that methane emissions from Tammar
wallabies amount to 1 to 2% of their digestible energy intake,
compared to methane emissions of roughly 10% of digestible energy
intake in sheep. In addition, marsupial and ruminant gut anatomies
differ, which influences how quickly food moves through the digestive
and his colleagues at CSIRO and the University of Queensland have
previously shown that marsupials have fewer methane-producing microbes
in their guts than do ruminants, and that certain bacteria in marsupial
guts might use up hydrogen and carbon dioxide that normally would be
used by methane-producing microbes to grow.
year, Morrison and colleagues reported that there were key bacterial
and enzyme-based differences between the gut contents of Tammar
wallabies and other herbivores, including cows. The scientists are
employing metagenomics, the application of DNA sequencing of organisms
and computational methods to study entire communities of microbes.
that complex microbial community of roughly 500 bacterial species in
the Tammar wallaby gut, the researchers determined that one of the
dominant bacteria there belonged to the Succinivibrionaceae family. The
researchers were able to isolate and grow this bacterium, called WG-1,
in culture to test and confirm its properties. It produces succinate as a
main end product of fermentation—not one of the usual end products
associated with higher methane production.
are also Succinivibrionaceae in the rumen; however, there has not been a
lot of focus on those bacteria, especially from the context that they
might contribute in any way to a reduction in methane production,”
Morrison said. “Our findings with the Tammar wallaby were a bit of a
surprise, but we think they provide an important clue for how rumen
fermentation might be directed away from methane formation.”
more analysis will be needed, he noted. Now that the researchers have
isolated and grown WG-1 in culture, they want to isolate bacteria in
livestock digestive systems that are probable distant relatives to the
wallaby bacteria. Better understanding of how these target bacteria
behave should help researchers figure out how to increase their numbers
and their contributions to livestock digestion, Morrison said.
hope that in the next few years, in addition to there being strategies
that inhibit the abundance of methane-producing microbes in livestock,
we will have identified how to augment the growth of other bacteria so
that feed digestion and fermentation remain optimal but also are
accompanied by reduced methane emissions,” he said.
work is supported by CSIRO’s Office of the Chief Executive (OCE)
Science Leader and Transformational Biology Capability Platform grant
programs, a CSIRO OCE Postdoctoral Fellowship and the U.S. Department of
Energy Joint Genome Institute Community Sequencing Program.
of the study include Phillip Pope, Wendy Smith, Stuart Denman and Chris
McSweeney of CSIRO Livestock Industries; Susannah Tringe, Kerrie Barry
and Philip Hugenholtz of the U.S. Department of Energy Joint Genome
Institute; and Alice McHardy of the Max Planck Institute for Informatics
and Heinrich-Heine University Düsseldorf. Pope is also affiliated with
the Norwegian University of Life Sciences and Hugenholtz is now the
director of the Australian Centre for Ecogenomics, based at the
University of Queensland.