I like potatoes, even if they spoil sometimes

Potatoes are very versatile. I like cutting them into small cubes and frying them with chorizo. I also like making tuna croquettes, hash-browns, and of course french fries. Potatoes are basically balls of starch and a super cheap foodstuff too. One of the drawbacks though is that since potatoes are so inexpensive, I inadvertently end up getting more than I can eat within a reasonable time span. Despite how hardy potatoes seem to be, I have embarrassingly forgotten to cook the lot and then found an overgrown, smelly surprise.

The ability of potatoes to grow bacteria actually has a history dating to the 19th century. Robert Koch, the founder of modern microbiology, used potatoes as he pioneered laboratory techniques. One of the fundamental principles of bacteriology is to conduct experiments on pure bacterial cultures. This is because the results of an experiment must be linked to a single, pure type of bacteria. Growing bacteria from natural samples can be challenging in itself, but an additional hurdle is to take mixed species of bacteria and parse them out into pure cultures.

In the 19th century there was no golden standard for growing bacteria. Scientists discovered that a potato slice could be used to grow bacteria from environmental samples (e.g. pond water). They observed that a colony of bacteria would grow from a single bacteria cell that made contact with the potato surface. From here, scientists could take a single colony of bacteria and move it to a new growth medium. This is called single colony isolation and it allows scientist to conduct experiments on single, pure species of bacteria.

Of course a difficulty arose in that potatoes slices aren’t good at growing many kinds of bacteria (this doesn’t stop our potatoes from going bad!). Robert Koch reasoned that using a nutrient-rich gelatin could expand the range of bacteria being grown, but a difficulty arose in that gelatin melts at 37 °C.  This temperature is the standard body temperature and it allows bacteria that grow on the body to grow optimally. To solve this conundrum, it was suggested to Koch to instead use agar in his growth media. Agar melts at high temperatures, but becomes solid once it cools down. Best of all it remains solid at 37 °C and as a bonus it results in clear media where we can visualize cultures growing.

Even today, laboratories used the versatility of agar to prepare growth media for many organisms. But as my pantry would remind you, potatoes can still hold their own as growth media so be sure to eat them before bacteria beat you to it!

Robert Koch (via WikiMedia)

Reference:
Madigan, Michael T., et al. Brock Biology of Microorganisms: Thirteenth edition. Benjamin Cummings: Boston, 2012. Print.