Bacteria are the smallest cellular organisms on Earth. They inhabit the planet for at
least 3.4 billion years, a lot longer than any other organism. The appearance of the 
modern humans occurred “only” 100-200 thousand years ago. 

Bacteria are therefore the most evolved beings on earth. They also replicate very 
quickly. For instance, bacteria of the Escherichia coli species can replicate every 
20-30 minutes under optimal growth conditions (nutrients in abundance, good 
oxygenation, optimum temperature and pH), but these conditions are rarely found 
in nature. Even if E. coli would double every seven hours, after one year, there would 
have been 1250 generations of bacteria. In human terms, whose generation time is 
about 20 years, this would translate into 25,000 years!

In an apparatus called chemostat, bacteria may grow in continuous culture conditions 
over long time periods, from a few hours to months. For example, a population of 
bacteria growing at a rate of 0.1 / h (generation time = 7 hours) will duplicate 100 times
in a period of 30 days. During this period of time, major changes occur in the genome, 
aiming at the adaptation of the bacteria to their environment.

We make use of the chemostat to track and understand the evolution of bacteria in 
real-time. Using this approach, we observe bacterial evolution in real-time. An evolution
 experiment that would be very hard or even impossible to do with multicellular 
organisms, can be easily performed with bacteria.