PROJECT DESCRIPTION

Overview

The cattle industry provides us with countless goods we eat and utilize today. From hamburgers and steak to dairy products to even some materials used to insulate your home, all these items are the by-products of cows from the cattle industry. However, in exchange for these commodities, the price we pay is the emission of methane gas into our atmosphere. In order to restrict this methanogenesis process occurring in the rumen, we are simultaneously pursuing the biosynthesis of bromoform in the rumen as well as the facilitation of nitrite reduction to ammonia.

Motivation

Methane production in the rumen of cattle is a serious issue, not only for our environment and our carbon footprint but also for the efficiency of the cattle industry at large. Our project is a double edged sword by attempting to solve both problems' common root cause.

In the 21st century, one of the the most pressing issues we all face is climate change. Earth’s average temperature is increasing at a dangerously fast rate and is affecting our planet in detrimental ways; glaciers are shrinking, heat waves are becoming more intense, and ecosystems are being destroyed. As the Greenhouse Effect shows, certain greenhouse gases are trapping the sun’s radiation and heat, causing climate change. The most widely recognized greenhouse gas is carbon dioxide as it is the greatest contributor to global warming. Yet there is another gas which is 25 times more potent at trapping the sun’s radiation than carbon dioxide, methane. According to the Environmental Protection Agency, a quarter of methane emissions is created by livestock alone, mainly cattle.

In our local state of Nebraska, the beef industry dominates above all others. There are over 6 million cows in Nebraska that account for 6.89% of all cattle in the US. This is the second largest number of cattle is one state behind Texas. (Cows per state ranking)Each cow releases 70 kg to 120 kg of methane annually, and coupled with the sheer magnitude of the cattle industry not only in Nebraska but across the globe, this has become a problem of increasing importance. If we are able to find a way to lessen the amount of methane produced by cattle, we as Nebraskans can help reduce the environmental footprint of our state.

Moving away from only the environmental aspect, another issue arises through the methanogenesis process as well. Methane production through enteric fermentation is a waste of feed energy for the animal. An average of 6.5% of the gross energy provided by a cow’s food source is lost here. By curbing methanogenesis, we may be able to help the cows utilize this energy themselves and in turn, benefit the cattle industry and the consumers as well. If we are able to increase the efficiency by even a mere 6%, about $20 per head of cattle could be saved. This could help drive down costs for local farmers to buy feed, and the price of beef could drop as a result.

The Problem

Methane is generated in the rumen of a cattle during its digestive process. The rumen is the first of four compartments of the stomach and functions to enzymatically decompose plant carbohydrates during enteric fermentation. When the cow consumes food sources such as grass, its unique ruminant microbiome allows it to digest the high cellulose content unlike the monogastric digestive system of other animals and humans. Three volatile fatty acids (VFA), acetate, butyrate, and propionate, are produced along with hydrogen and carbon dioxide. While the VFA’s follow one pathway and become energy for the cow and the microbiome living inside of it, the hydrogen and carbon dioxide are instead used as substrates for the methanogenesis process. In this process, methanogens, microorganisms of the domain Archaea and phylum Euryarchaeota, convert the two gases, hydrogen and carbon dioxide, into methane. At the end, most of the methane is expelled from the rumen when the cow belches the gas into the air.

What can we do?

There is research going on all over the world that is working on lowering methane production in cattle. Common approaches involve diet changes, such as feed additives, that indirectly change the microbiome. The efficiency of these approaches can be vastly improved by directly changing the microbiome of the cow with genetically engineered bacteria.

One way to do this is by using the powers of seaweed. Surprisingly, humans have been feeding seaweed to cows in coastal regions since the time of the ancient greeks.[1] Seaweed is now being studied as a food additive because it has been shown to reduce the amount of methane produced by cattle. The compound within seaweed that is responsible for reducing methane is bromoform and other related molecules such as bromochloromethane. Bromoform works by inhibiting the efficiency of the methyltransferase enzyme by reacting with the reduced vitamin B12 cofactor required for the second to last step of methanogenesis.

A study done by Australian scientists tested 20 different species of seaweed on methanogens found in the stomachs of cows. They discovered seaweed reduced methane production by up to 50 percent, depending on the amount administered. But methane reduction at notable levels required high doses of seaweed, almost 20 percent by weight of the sample. This worked fine in the lab, but outside of the lab this large percentage of seaweed would be difficult to implement and would likely have a negative effect on cow’s digestion.[2] On top of this the bromoform produced by the seaweed farms is known to act as a catalyst for recombination of ozone. In fact the ability to deplete ozone can be 10-20 times higher than the more well known molecule Freon-22. This is due to the high resistance of bromine to the termination reaction of ozone.[3]

These observations led our team to directly change the microbiome of the cow with E.coli that produces bromoform instead of using seaweed to deliver the bromoform. To do this our team took the gene from the algae Corallina pilulifera that codes for the enzyme bromoperoxidase and cloned it into E.coli.

The bacteria would be fed to the cow along with the necessary substrates as a food additive. Having the E.coli produce the bromoform inside the rumen of the cow gives us the power to control when the bromoform will be produced. We have designed a genetic circuit that will only express the gene for bromoperoxidase when the bacteria is inside the cow, and if it exits the cow a kill switch will be activated that will cause the bacteria to die. (link to killswitch description that will be placed somewhere else) This approach makes it so that the bromoform is only produced and used up within the rumen itself; allowing our ozone to remain intact.

A proven dietary intervention strategy for reducing methane production in cattle is a nitrate supplement. The nitrate works by competing for hydrogen ions within the rumen that are usually used by methanogens. (Rumen pathway showing H+) Using these ions, the nitrate is quickly reduced to nitrite. Unfortunately, the conversion from nitrite to ammonia is a very slow process. This combination leads to a nitrite accumulation in the rumen and can cause serious health issues for the cattle or even death.

To avoid this issue, we are introducing bacteria that produce an enzyme called nitrite-reductase. This enzyme facilitates the conversion from nitrite to ammonia and is found naturally inside the rumen at low levels.

Continue the story HERE!