Atlant’s Column: Feeding Frenzy in the Gut

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Welcome to the section on which explores, analyzes and explains fascinating microscopical structures.

Intestinal BacteriaBacteria are the heroes of our digestion. They split carbohydrates for us, supply us with essential vitamins and protect us from intestinal diseases.

Text by science writer Atlant Bieri
Photography by Martin Oeggerli

This is a tiny specimen of human faeces. The rods and cones are bacteria occurring in astronomical large numbers in our intestine. Every millilitre gut content harbours up to one trillion of them. There, they engage in one of the biggest feeding frenzies on our planet. 24 hours a day, they gorge themselves with chocolate, pasta and veal.

That they help themselves in an all-you-can-eat style to our food is not a cause for concern. On the contrary, they help us to split indigestible foods into their component parts. The chemical spectrum of our intestine is not broad enough to do this. The bacteria on the other hand cope with almost anything because of their high diversity.

The enzymes they produce, are able to break up complex carbohydrates such as starch and various sugars. Once the bacteria are done with them, they are on hand as short chained fatty acids. They are small enough to pass the intestinal mucosa and enter our blood stream, which transports them to all the cells of the body where they are used as fuel.


Fly proboscisIncompletely Digested Plant Fiber

However, there are also substances which even bacteria cannot crack that easily. These include for example plant fibres. One of them runs right across the image. It is made up of very long carbohydrate chains that resemble in their microstructure a synthetic polymer and thus withstand all sorts of chemical attacks. Our gut bacteria only cope with a small part of them. The rest we discard undigested.

Altogether, more than 33’000 different species of bacteria have been identified in the human intestine. According to estimates by researchers there are at least five hundred different species of bacteria growing in a healthy intestine. Some of them not only digest but also produce vitamins such as vitamin K, which makes blood clotting possible, or vitamin B12, which plays an important role for cell division and the function of the nervous system.

Fly proboscisOne of the most important bacterium is Escherichia coli, which is visible as turquoise-coloured rods on the image. It is so numerous that it covers the entire intestinal mucosa like a single carpet. In this way it protects us from infections, such as salmonella, which cause diarrhea. If we ingest the pathogen with contaminated food, it finds no place to insinuate itself and multiply thanks to the living shield on the intestinal mucosa. Thus, without causing any damage, it ends up in the toilet.

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Continue reading Atlant’s Column: Cyclops in a Kilt , August 2013, or go back to the archive