Don't touch my coffee!

Some researchers going after the microbiome of everyday-items don't shy away from anything - not even from one of the holiest items in the household: the coffee machine [1]!

It's not particularly surprising that coffee machines are sprawling with bacteria. They are warm and moist - bacteria's paradise! But the surprising part: there are caffeine-degrading bacteria in coffee machines. Yes: CAFFEINE. DEGRADING. BACTERIA! Scary, huh? Does that mean I've been drinking decaf all along? How I am supposed to generate love for bacteria if they dare touching my coffee? They should know better than to touch a Ph.D. student's coffee!

Well, the good news is: the caffeine-degrading bacteria were found in the waste containers of common capsule coffee machines [1]. Unless you are so desperate for caffeine that you drink out of the drip tray, your caffeine supply is safe. The same study found no indications, that these bacteria were actually found in the coffee capsules, so the bacteria only come into play after you've had your coffee.

How come that bacteria can degrade caffeine in the first place? Chemically, caffeine belongs to the group of "xanthines". Xanthine is a precursor for guanine - one of the bases in the DNA. Hence, bacteria that degrade caffeine to xanthine have an additional source for this building block of their DNA. There's even an example of bacteria that are literally addicted to caffeine [2]! Normally, bacteria can synthesize xanthine to make guanine to use in their DNA. Researchers have engineered a strain of Escherichia coli that can not synthesize xanthine anymore, but instead these bacteria can degrade caffeine to xanthine, which they normally can't. This strain is addicted to caffeine! It can only grow in the presence of caffeine, because it needs it to make xanthine so it can build its DNA. And you thought you needed coffee to live...

Structural similarity between caffeine (left) and xanthine (right). Source: PubChem

Caffeine-degrading bacteria are interesting in another aspect: Caffeine is a water pollutant, but wastewater treatment can remove it [3]. The presence of caffeine in the environment indicates that  untreated sewage is entering the environment. Coffee beans undergo processing before they are the black elixir in your cup and this process uses a lot of water. Caffeine-degrading bacteria could give insights how to clean up the mess we are making to make Monday mornings a little bit more bearable.

Sources: 
[1] Vilanova, C., A. Iglesias, et al. (2015). "The coffee-machine bacteriome: biodiversity and colonisation of the wasted coffee tray leach." Scientific Reports 5: 17163.

[2]Quandt, E. M., M. J. Hammerling, et al. (2013). "Decaffeination and measurement of caffeine content by addicted Escherichia coli with a refactored N-demethylation operon from Pseudomonas putida CBB5." ACS Synth Biol 2(6): 301-7.

[3] Buerge, I. J., T. Poiger, et al. (2006). "Combined sewer overflows to surface waters detected by the anthropogenic marker caffeine." Environ Sci Technol 40(13): 4096-102.