The Science Bit: Part 1 – Digestive bacteria

20 05 2010

BioMed Central has now published my first column for the staff magazine so I am now delighted to be able to share it with you. Here’s the first installment for your reading pleasure, ever-so-slightly edited to remove BMC in-jokes…

If you’re reading this on your lunch break, then so much the better. Digestion, the process of breaking down the food you have just eaten into tiny, absorbable molecules, is a complex and wondrous thing. Much of the process is controlled by enzymes – protein molecules that speed up the numerous chemical reactions needed to turn your hunks of cheese and bread into particles small enough to pass through a microscopically thin membrane in your small intestine and into your bloodstream.

It’s mindboggling. In your mouth, enzymes in saliva break down some of the carbohydrates in your food and your teeth mash it all up with the liquid so that you don’t choke on chunks of dry bread when you swallow. Muscles in your oesophagus squeeze the food down your throat, it then sits in a stomach acid bath for about an hour and passes into your small intestine. More enzymes and chemicals of all different types are added to the partly digested food and eventually, all the useful molecules from your cheese sandwich end up in the blood. From here, they are transported to wherever they are needed to take part in new chemical reactions, perhaps even ending up as a salivary enzyme again.

This complex process has a flaw – we’re pretty rubbish at digesting fruit and vegetables. Since we don’t make the right enzymes needed to digest all of the plant matter that is good for us, we’ve enlisted the help of bacteria. FYI: you don’t get these bacteria from eating probiotic yoghurts – they’re already there (although the yoghurts may help to replenish them if you’ve been ill and, ahem, flushed them all out). Bacterial enzymes break down the things that our enzymes can’t; the bacteria take some of the nutrients, we take some of the nutrients and everybody’s happy.

A new piece of research in the journal Nature suggests that the enzymes of bacteria in the guts of people around the world may be different, depending on regional diet. In a collaboration between French and Canadian scientists working in Japan, researchers found that bacteria in Japanese guts contained genes from an external bacterium found on seaweed. They believe that in swallowing seaweed-wrapped sushi, surviving sea bacteria on the nori may have transferred their genes to the bacteria in the intestines, thus empowering the intestinal bacteria with the ability to digest seaweed. Since Japanese people eat a lot of seaweed – approximately 14 grams per day – that’s a pretty big boost to their digestive systems.

The study was only small, but it is the first time that bacteria outside of the body, from a completely different ecosystem, have been found to alter the bacteria inside the body. With further research, we may well find that microorganisms, like the nori bacteria, help to shape and evolve the human body and our behaviour in more ways that we previously thought.

Reference: Hehemann et al, Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota, Nature 464, 908-912 (2010)

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