Wallabies eat essentially the same diet as cattle, but produce one-fifth… (Justin Best, Associated…)
Scientists have isolated a bacterium from the gut of Australian Tammar wallabies that allows them to consume and digest grasses, leaves and other plant material without producing copious amounts of methane, as cattle do.
The microbe was discovered through a process described in a study published online Thursday by the journal Science. Ultimately, it might be put to use to reduce the carbon footprint of cows and other ruminants, said study coauthor Mark Morrison, a microbial biologist at the Commonwealth Scientific and Industrial Research Organization in Queensland.
"Now that we have that picture [in wallabies], we should be able to look at livestock and find ways to try and replicate it," Morrison said.
The methane-rich burps and flatulence of livestock have been blamed for 28% of that greenhouse gas' global emissions due to human activity. Like other cud-chewing mammals, they produce methane as their systems work to break down and ferment the plant matter they eat.
Wallabies, close relatives of the kangaroo, eat largely the same diet as ruminants and also host microbes that help to partly digest their food. But they produce just a fifth as much methane as ruminants do.
Previous efforts to catalog the constituents of the wallaby gut's microbial soup revealed that wallabies were full of a then-unidentified bacterium that was perhaps responsible for the difference.
To study this key microbe, the researchers would have to get it to grow on its own. So Morrison and colleagues took samples from wallaby guts and genetically analyzed the whole community. They figured out that their target bacteria — which they dubbed WG-1 — was related to the family of soil bacteria called succinivibrionaceae. They looked at genes they knew must be associated with WG-1 and tailored the growth medium to those genetic specifications.
Certain genes they found told them the critters preferred to eat starch over other sugars. Other genes showed that they obtained their nitrogen by consuming urea, rather than in complex amino acids. They also found a gene that indicated the bacteria were resistant to the antibiotic bacitracin, which they then used to kill off other interfering microbes. The target bacteria thrived.
As suspected, the microbes produced a chemical compound called succinate instead of methane. Unlike methane, which cannot be put to further use by the body and must be expelled, succinate can be broken down into propionate by other gut microbes, which can then be used by the host animal.
Thus, having more succinate-producing bacteria allows wallabies to get more nutrients out of their food in addition to being eco-friendly, Morrison said.
This line of research will help scientists understand how some bacteria help animals break down food and extract nutrients — and may even give them clues on how to manipulate that process in the future, Morrison said.
But the work won't produce low-methane cattle anytime soon, said Robert Forster, a microbial ecologist with Agriculture and Agri-Food Canada in Alberta, who wasn't involved in the study.
Though ruminants do have relatives of WG-1 in their systems, they don't seem to flourish, let alone dominate — and that might be because they're not as well-suited as methane-producing bacteria for the long-term churning that goes on in the cow belly, he said.
The study, he added, "gives us a bit more of an understanding as to why there's less methane production in wallabies, but it doesn't give us a way as to how we could use it to lower methane production in ruminants. That's a big leap."