Researchers at Aarhus University (Denmark) have launched a project to produce cellulosic bioethanol via completely natural processes. They are looking for the solution in the intestines of pandas and slugs, and in ants’ fungus gardens—special enzymes and microorganisms that, for millions of years, have specialized in the breakdown of this particular material.

Among other things, we’ve collected a large amount of panda poo, and incubated the bacteria in the laboratory. We then fed bamboo to these bacterial colonies and found that they can very quickly break down lignocellulosic biomass into ethanol, lactate and hydrogen. The microbial culture that has developed in the gut of pandas seems to be quite unique.

—Associate Professor Alberto Scoma, heading the Engineered Microbial Systems research group

In a study published this year in the Journal Frontiers of Microbiology, Scoma and his team collected gut microbiomes from fresh fecal samples of a giant panda (either entirely green or yellow stools) and supplied them with green leaves or yellow pith (i.e., the peeled stem). Microbial community composition was substrate dependent, and resulted in markedly different fermentation profiles, with yellow pith fermented to lactate and green leaves to lactate, acetate and ethanol, the latter to strikingly high concentrations (∼3%, v:v, within 3.5 h). Scoma et al.

Characterization of green and yellow stools from giant panda. Squares of the same color represent each a single replicate (n = 3), with black dots or lines indicating the mean. Scoma et al.

Scoma came up with the idea for the project during a visit to a zoo in Belgium. While watching two new panda arrivals, he came to think about how strange it is that a bear can live almost exclusively on bamboo.

Pandas are bears, and in terms of physiology, they are carnivores. Nevertheless, up to 99% of a panda’s diet is bamboo. It takes just 5 to 12 hours before the lignocellulosic biomass of which bamboo consists is excreted.

If a heavy Panda can feed itself with lignocellulosic biomass with a digestion time of only up to 12 hours, its digestive system must be really good at breaking down the material. Pandas eat a lot of bamboo per day, about 10 kg. So, the microbes in the gut are used to receive a high amount of lignocellulose and must process it very quickly. We can do something useful with microbes like these. Therefore, we’re trying to understand the process in detail, so that we can repeat it in the laboratory, and hopefully use it in industry in the future.

—Alberto Scoma

Working with Stine Slotsbo, special consultant, Hans Joachim Offenberg, senior researcher, and Jesper Smærup Bechsgaard, all from the Department of Bioscience, and with Thomas Boesen, Associate Professor at the Department of Molecular Biology and Genetics, Associate Professor Alberto Scoma has included other species in the project—species which, like the panda, also digest lignocellulosic biomass.

Portuguese slugs (Arion lusitanicus) and leaf-cutter ants (Atta cephalotes) were an obvious choice for the project, as both species feed on similar biomass. Slugs, like pandas, by eating it directly, while the ants use fungi to break down the biomass for them.

Evolution always finds a solution, as long as it has enough time. Now it's just up to us to understand the complex microbial degradation, so that we can take the relevant enzymes out of the equation and test them in vitro, and I hope that then we will be able to find out exactly what the enzymes are capable of. We’re using millions of years of evolution to solve a modern problem.

—Hans Joachim Offenberg

Resources

• Scoma Alberto, Khor Way Cern, Coma Marta, Heyer Robert, Props Ruben, Schoelynck Jonas, Bouts Tim, Benndorf Dirk, Li Desheng, Zhang Hemin, Rabaey Korneel (2020) “Substrate-Dependent Fermentation of Bamboo in Giant Panda Gut Microbiomes: Leaf Primarily to Ethanol and Pith to Lactate ” Frontiers in Microbiology doi: 10.3389/fmicb.2020.00530