The carbon fallacy    -    Cows are not cars   (pdf)

In discussions about climate change, all carbon emissions are seen as equally bad. It is saddening to observe that even a quality journal like Nature includes cattle-produced methane when calculating greenhouse gas emissions from food and comparing these to those of electrical appliances that are powered by fossil fuels.

Carbon released by livestock, mostly methane and carbon dioxide, is derived from plants. This “surface carbon” will be incorporated from the atmosphere back into plants and other photosynthetic organisms within days, years or centuries. However, the “deep carbon” released from oil, coal and gas by power plants and combustion engines will not be put back in its original form (buried deeply under earth's surface, inaccessible to the atmosphere) for millions of years.

Cycling of “surface carbon” by herbivores and plants has been part of life almost since its inception. Large ruminants, such as the bison herds roaming US prairies in the past, have been belching methane into the atmosphere for millions of years as part of the natural carbon cycle. This cycle has only been broken since humans started releasing “deep carbon” into the atmosphere by combusting fossil fuels. Capturing of anthropogenic carbon in million-year repositories will likely be required to decrease atmospheric carbon to pre-industrial levels.

Vandenbergh and Steensen Nielsen (2019) Nature Climate Change 9:8

Camilleri et al. (2019) Nature Climate Change 9:53

Potential breakthrough in crop yield and carbon capture

Photosynthesis is the key process enabling plant growth and life on earth. It is also a great way to capture carbon dioxide from the atmosphere into biomaterial. However, the efficiency of photosynthesis is limited by photorespiration, which helps plants to reduce the buildup of oxygen gas in their leaves without losing moisture.

South and colleagues engineered more efficient photorespiratory pathways into tobacco plants while inhibiting the native pathway. This increased photosynthetic efficiency and vegetative biomass by up to 40%. The authors are optimistic that similar engineering of crops may improve their yield, which would help nourish the increasing human population. They don’t mention it, but I would assume it would increase carbon capture by plants as well, helping to reduce the buildup of fossil fuel-derived carbon dioxide in the atmosphere.

South et al. (2019) Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field. Science 363:45.

Trouble brewing in our gut?

Researchers estimate that bacteria in the human intestine contain over 6000 genes that encode antimicrobial resistance (AMR). AMR is a health concern because it can make treatment with antibiotics ineffective.

The good news is, transfer of AMR genes from gut microbiota to pathogens is probably a very rare event. This makes sense. Antimicrobial resistance is a weapon in the never-ending war between bacteria, and it is good practice to stick to your guns rather than share them with others.

The bad news may appear to be the large number of antimicrobial resistance genes in our gut microbiota. However, initial results indicate that this is not the result of antibiotic use, as treatment of patients with antibiotics reduced the variety of AMR genes.

Antimicrobial resistance genes have been present for millions of years in the environment and may likewise have protected human gut microbiota from natural antibiotics long before we discovered penicillin. While we need to more deeply investigate gut-dwelling AMR genes to better understand the safeguards against their transmission to pathogens, at the moment I’m not losing sleep over them.

Ruppé et al. (2019) Prediction of the intestinal resistome by a threedimensional structure-based method. Nature Microbiol. 4:112.


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