How do bacteria adapt to new environments?

By reproducing in huge numbers.





Oversimplification:


Say you've got 1% variation in your genes, so 1 out of every 100 bacteria that derive from you (a bacterium, in this case) is just a teensy-weensy bit different than the others.





If you make millions of offspring, MOST are going to be like you, but some of them are going to be different... (sort of like the brothers and sisters from the same parents aren't all the same.)





Every now and then, one of those differences is going to make the bacteria breed easier.





So say you normally live in salt water, but there is a protein you can make that helps you live without salt... maybe you make enough of this protein that you can survive, oh, fresh water from rain running into your salt water.





Now, say one of your offspring makes a LOT of this protein...





...Now, the offspring of THAT offspring is going to live through the water stopping being salty, right?





If the water then went totally fresh, and the new bacteria were all derived from your one weird offspring, your family of bacteria will be said to have adapted...because now you ALL make that protein. (or you died.)