Here’s a cautionary tale for microbiologists everywhere. The bacteria you put to bed at night may not be the same as the ones that you awake in the morning.

This is news to me. I thought an E. coli was an E. coli, whichever way you cut it. Beloved, trusty, experimental ally of molecular biologists. Only get really interesting when they acquire the suffix 0157 and swarm over contaminated meat.

Steven Finkel of the University of Southern California presented a whole host of evidence showing that E. coli are far more fickle than we thought. In one experiment, he started out with 50 identical cultures of the bugs, left them to grow for ten days and then examined the sequence of one gene in each. Three-quarters of them picked up mutations in that gene, and these mutations were of 180 different types.

When he left the bacteria for several months, many of them had chopped out large chunks of their entire genome, discarding 50 or 60 genes like they were unnecessary baggage. Finkel says that the bugs even smell different after ten days, and turn different shades of yellow.

So what? Well, if you’re a microbiologist – analyzing a particular gene in your bacteria, say – this might matter. Many people throw their cultures in the fridge overnight, and come back to analyse them in the morning, or next week, or next month…

Finkel’s results suggest that such a neglected culture might have changed, so that it now contains numerous different bacteria with different genetic make-ups; ten identical cultures could have become ten different ones, although most people don’t know it. He says that microbiologists get nervous when they hear his talk.

There are certainly a lot of perspiring scientists around. But I think that’s more to do with this being sticky Orlando in summer.