Bacteria Made Your Lunch

Cows that house bacteria


I was thinking of doing a post with a title like ‘In defense of cows’ or something along those lines.  This is not just because I’m a sort of carnivorous and contrarian guy (which I am), but because cows can actually do something that is objectively remarkable.  I know that lots of the readers on this blog are vegetarians or even vegans, and that is fine as a life-style choice for you. But no matter what your personal food choices are, it is worth thinking about what cows can do for the rest of us.

What Cows Do

One of the most abundant natural, organic chemicals in the world (cellulose), is something we humans can’t digest at all.  Cows are cool because they can eat cellulose and turn it into human-edible foods like milk and meat.  The reason that I switched the title of the post is that it isn’t actually the cows that should get the credit for this feat, at least not most of it.  Cows (and other ruminants like sheep, goats, bison, camels, llamas, yaks, water buffalos…) can only make this conversion because of the bacteria that they house in one of their stomachs.  In the whole world, there are only a few bacteria and a few fungi that have the capability of turning cellulose (the main structural polymer of all plants) back into the energy-rich, glucose sub-units of which it is made (bacteria also do that job for termites!).

I can relate to why many people have ethical issues with aspects of how beef or milk is produced today. But that does not, at least for me, mean that we should abandon the idea of harnessing the remarkable microbial process that has allowed ruminant animals to be such an important part of the human food supply in diverse cultures for millenia.  In fact I would like to see us refine not just the “animal wellness” aspect of this industry, but also its greenhouse gas issues.

What We Wish Cows Didn’t Do

The climate change “down-side” of ruminants is that they are an extremely important source of the potent greenhouse gas, methane.  Some of that comes from the manure they generate, but at least there is a well developed technology for that could turn that waste stream into “carbon-neutral” energy using methane digesters.  Much more of the methane comes from the cow’s “burps” and some from “flatulence.”  This is true of both “range fed” and “feedlot finished” animals.  The methane is generated by non-beneficial bacteria that also live in ruminants stomachs and which are actually robbing the animal of some energy and making this problematic greenhouse gas at the same time.  We need to figure out how to safely reduce or eliminate this inefficiency through feed management, probiotics or something. I’m not an animal scientist, but I know those folks are working on this problem.

How We Get Protein

But the good, ruminant bacteria aren’t the only ones making our collective lunch.  Just as cellulose is a huge energy source unavailable to humans without the help of bacteria, nitrogen in the atmosphere is a huge, but mostly unavailable source of what it takes to make the protein we need.  Once again, there are a small number of bacteria that are able to turn the seemingly inert, di-nitrogen (N2) in the air into the forms of nitrogen that can be assimilated by plants (nitrate, ammonia, urea…).  Some of this occurs in aquatic systems by cyanobacteria and we benefit from it through the food chain it supports.  Some of it occurs through free-living bacteria like Azospirillum that lives on the surface of tropical grasses like sugarcane.

Picture of an alfalfa nodule

The main way that we humans benefit from these remarkable bacteria is through the services of “legumes” which are plants that form a symbiotic relationship with a “nitrogen-fixing” bacterium called Bradyrhizobium that provides the plant with biologically available nitrogen in “trade” for the glucose that the plant can make using solar energy.  World-wide, farmers take considerable advantage of these bacteria to be able to grow crops that don’t need much, if any, added nitrogen fertilizer. I looked up the FAO statistics on global crop area, and 18.5 percent of the land planted to food crops are legumes even without considering animal feeds like alfalfa.

We can’t get all our nutritional or food enjoyment needs from legumes.  Ruminants have their place in the food supply, but it is not all we need.  Still, as a “technology guy,” I’m humbled by the contribution that these “lowly” and ancient bacteria make to our survival. No matter what your food choices are, we all depend on bacteria.

You are welcome to comment on this post or to email me directly at

Legume nodule image from ninjatacoshell

Cows image from jrubinc

Written by sdsavage

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