Robot Measures Exponential Growth

The plan was to grow harmless probiotics like lactobacillus on some agar media. We would repeat a previous experiment adding different hand washes and cleaning products to see which was most effective at sanitising them. And try a second experiment using the same yogurt brand but of different use by dates to see how many bacteria they retained (via serial dilution). The lab robot was going to be used to remotely monitor their growth on the petri dishes in the lab over the warm bank holiday weekend.

This required making a now close to mythical lactose-yeast extract media made in a previous experiment. Mythical because it failed again on attempt 6 with the milk protein precipitating out.

A previous failed attempt at getting a milk powder-yeast extract agar. Pure milk powder and agar on the left works fine. Different concentrations of yeast extract in the centre and right… which have precipitated out / denatured the milk powder proteins… again

With the robot ready to roll and the media decidedly lumpy we abandoned the planned experiments, poured the media into an open plastic container and left it to nature’s devices.

On returning a couple of days later it was decidedly dried out and non inhabited. We doused it with some pure water and left it again for the weekend. It was quickly investigated by some fruit flies… where do they come from?! And within 12 hours was showing some mould growth. Within a few days it was pretty unrecognisable! … and slightly too characterful

Decomposers and fruit flies getting to work!

We applied a simple threshold filter on the red channel (making blue and green maximum) to the pictures to get the following data:

If we assume the growth is in 3 dimensions; as the mould grows into the agar media, then we’re reminded that nature grows exponentially when given the right conditions!

If you’re wondering what happened to the mould… bleach. Lots of bleach.

Source code here.

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