Can red seaweed be the solution for cow burps?

Originally published for MicroBites on October 30, 2023

Archaea get a lot less airtime compared to the other two domains of life—Eukarya and Bacteria. Bacteria tend to outnumber Archaea in most environments, particularly in gut of animals where Archaea make up only about 1-2% of microbes depending on the animal. Despite being such a small minority of the microbial population, Archaea have managed to make a big impact on our environment. Some Archaea have the ability to produce the greenhouse gas methane. These Archaea, referred to as ‘methanogens,’ find homes in anaerobic conditions like deep-sea hydrothermal vents and hypersaline soda lakes, but the place where they impact us the most is in the digestive tract of cattle.

Figure 1. How cattle produce methane. Archaea in the rumen, the first compartment of a cow’s four chamber stomach system, utilize hydrogen gas and carbon dioxide to produce methane, which gets burped out as the animal digests and ferments the roughage in its feed.
Source: https://asm.org/Articles/2023/June/Ruminant-Methanogens-as-a-Climate-Change-Target

Cattle are a type of grazing animal known as a ‘ruminant.’ This refers to the multi-compartmental system with which they digest their food. This system contains four compartments. The first two compartments—the rumen and the reticulum—are abundant with microbes where they ferment the fibers and starches found in the ruminant’s cud. The cud is then passed to the omasum where fatty acids and ammonia get absorbed before making it to the final chamber—the abomasum—which functions similarly to the stomachs of most other mammals. In this process, particularly in the rumen where the bulk of the fermentation occurs, methane is produced and released into the atmosphere as a burp. Ruminal methanogens account for 17% of global methane emissions—more than the 15% emitted by fossil fuels. For this reason, Archaea have garnered the attention of researchers who are looking for a way to curb emissions on this front.

In the past 5-10 years, there has been a growing interest in using seaweed to curb methane production by ruminants. By adding certain species of red seaweed, farmers can lower the amount of methane that gets produced by inhibiting the methane production pathway. A recent study did a deep dive in the microbial makeup of an in vitro rumen treated with three species of red seaweeds—Asparagopsis taxiformis, Palmaria mollis, and Mazzaella japonica. A. taxiformis has been previously shown to strongly inhibit methane production. It is native to Australia and New Zealand but has become invasive in many other parts of the world. In an effort to find other species of seaweed that may have an inhibitory effect on methane production, this group of researchers also treated rumen with P. mollis, a red seaweed found on the coast of the North Pacific, and M. japonica, which is native to the Asiatic Northern Pacific Coast.

Figure 2. A rumen simulation technique (RUSITEC) system. Rumen from a donor cow gets filtered and separated into the solid contents and the liquid contents. The solids get placed in a nylon bag with small pores just large enough for microbes to get through, and the liquids fill the surrounding container. A second nylon bag of fresh ‘feed’ gets placed in with the rumen solids and every 24 hours one of the bags is replaced as the microbes ferment the contents of the bags. Synthetic saliva buffer is pumped into the container to replenish the liquids as an electromotor mimics the movement of the rumen to churn everything inside. Displaced fluid is collected in an effluent flask and the gas from fermentation is collected in a gasbag for analysis. Created with BioRender.com.

The researchers inoculated several in vitro ‘rumens’ with microbes sampled from a donor cow, then treated each rumen with a different red seaweed and left them to ferment for a total of 21 days. Adding seaweed to the rumen was an incredibly disruptive event for the microbes, so they monitored the microbial community by sampling the microbial DNA and sequencing it to determine what species of microbes, and what proportion of each microbe were in each sample. Of the three seaweeds tested, A. taxiformis was the only one to make a dent in the microbial makeup. P. mollis and M. japonica did not appear to have an effect. This is likely due to A. taxiformis being the only seaweed of the three to produce bromoform, which is the agent involved in methane production inhibition.

In a companion experiment to this study by Terry et al., rumen treated with A. taxiformis reduced the amount of methane produced by 95%. That decrease can be attributed to an almost complete wipe out of methanogens in the A. taxiformis treated rumen in this study. This on its own is great news for farmers who are looking for ways to curb methane emissions. However, the overall picture is not that simple. While the seaweed is meant to target the methanogen community, there were some shifts in the bacterial makeup that could pose a problem in vivo.

The companion study showed a reduction in fermentation activity, which can be attributed to a reduction in Fibrobacter species of bacteria. Fibrobacter species are some of the microbes in charge of breaking down cellulose in the rumen and are important to make nutrients available for absorption down the line. Prevotella species, which are the most abundant microbial genus in the rumen, also saw a major shift, increasing in abundance by 1.6-fold while the microbial community stabilized. A majority of the core bacterial species in the rumen were impacted in some way throughout the 21 days of seaweed treatment. This microbial shift resulted in an overall depression in fiber degradation and microbial activity, which could be detrimental to the health of an animal being fed this altered diet.

Red seaweed, A. taxiformis in particular, could still be a workable solution to agricultural methane emissions. Start-ups based in Sweden and Hawaii are working to find ways to efficiently cultivate A. taxiformis for the express use in agricultural feed, and while these efforts are still in the early days, the hope is to scale the production of this feed supplement to make it widespread practice. However, the health of the animal should be taken into careful consideration. While shifts in the gut microbiome are within the realm of normal, there is a lack of comprehensive, long-term studies on how this change in feed affects various livestock. It is important that science leads the charge where animal health and climate change is concerned.

Original paper: Comparative analysis of macroalgae supplementation on the rumen microbial community: Asparagopsis taxiformis inhibits major ruminal methanogenic, fibrolytic, and volatile fatty acid-producing microbes in vitro.
Companion paper: Evaluation of Rumen Fermentation and Microbial Adaptation to Three Red Seaweeds Using the Rumen Simulation Technique.