The human population has grown from approximately 2.6 Billion in 1950 to around 7.8 Billion nowadays (United Nations, 2021). A secondary effect of this growing population is also an increase in the demand for food , for instance red meat originating from cows, sheep and goats.
Cows, sheep and goats belong to the suborder Ruminantia, meaning that they have a four chambered stomach, the first one of which is the rumen (Britannica, 2019). Within the rumen, microorganisms can digest cellulose taken up as grass, hay, straw etc., into compounds that can be taken up by the animal as an energy source. During these processes, side products such as CO2 and H2 are produced (Matthews et al. 2018). These compounds are used by archaea in the rumen to produce methane (CH4) (Kinley et al. 2020). These archaea are also referred to as methanogens.
CH4 is a greenhouse gas that has a higher potency than CO2. This means that, although there is less of it in the atmosphere, its global warming potential is 86 times stronger than CO2 per unit of mass over a timespan of 20 years and 28 times stronger on a timespan of 100 years (Jackson et al. 2020).
The upper graph shows global methane parts per billion (ppb) from 2000 to 2017, with the red line showing seasonal variations and the blue line showing a non-seasonal trend. The lower graph shows the amount of delta C-13 isotope ratios in methane over the same timeframe, showing a negative trend. This trend can potentially be linked to microbial produced methane (Fletcher & Schaefer, 2019).
Since global warming is an ever-increasing problem worldwide, CH4 emissions from ruminants, especially cows, are getting more and more attention. Therefore the emission of methane from ruminants has been experimentally reduced in various ways. One method of reducing the methane output by ruminants is the usage of the red seaweed Asparagopsis taxiformis, which, depending on the feed amount, could reduce methane output by up to 98% (Kinley et al. 2020). Of the many ways of reducing methane emission, A.taxiformis shows the strongest dose-dependent methane mitigating effects, while having the least impact on rumen fermentation (Chagas et al. 2019).
This methane reducing ability of A. taxiformis is due to it being capable of generating halogenated compounds, amongst them bromoform (Machando et al. 2017), which is the major halogenated product of these red algae (Machando et al. 2016).
Bromoform has the ability to inhibit a cobamine-dependent methyltransferase, which is required for the synthesis of methyl-coenzyme-M, the key enzyme in the final part of methanogenesis (Machando et al. 2016), ultimately reducing methane production if present in the cow rumen (Kinley et al. 2020). These methyl-coenzyme-M enzymes are present exclusively in methanogens (Zhu et al. 2021), whereof the archaeal genus Methanobreviacter is the most abundant and most studied (Danielsson et al. 2017).
The life cycle of A. taxiformis consists of three life stages, which unfortunately means that aquafarms have yet to grow these algae through all life stages, meaning that the cycle could not be closed. This hinders the farming of the species on a global scale dramatically (Zhu et al. 2021).
In 2020, Thapa et al. identified the genes from different groups of A. taxiformis which are involved in the production of bromoform, as well as the genes involved in bromoform production in the algae Chondrus crispus, amongst others. The A. taxiformis genes were named Mbb1, Mbb2 and Mbb4, the C. crispus genes CcVHPO1 and CcVHPO3.
Thapa et al. (2020) successfully expressed bromoform in E.coli bacteria. Our team tries to recreate this transformation and expression. Our aim is to produce a microbial feed for ruminants. This feed contains encapsulated E.coli which have the genetic ability to produce bromoform, thereby inhibiting methanogenesis within the cow. Due to E.coli already being naturally present in the rumen, colonization may mean that this feed additive only needs to be administered once in a cow’s lifetime (Khafipour et al. 2009).
If successful, this feed additive is a great demonstration of the power and opportunity that synthetic biology has to offer. If applied for causes like reducing greenhouse gas emissions, synthetic biology will be put into the worldwide spotlight, and can be more approachable and appreciated by the general public.
After adding said feed additive, these cows will not only have reduced methane emissions, but potentially also have increased weight gain. This is due to energy not being lost in the form of methane, but being preserved within the animal (Kinley et al. 2020).
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