|We all know cash can be super dirty! <SOURCE>|
As far as methods go, the research group relied on pretty standard shotgun metagenomic sequencing approaches. As a brief refresher from a previous post discussing these methods, this means the microbial genomes (including bacterial, fungal, etc) were sequenced. This allowed the researchers to see what kinds of bacteria were present on the bills, and what kinds of genes these microbes contained (allowing predictions about functionality). To get the DNA from the cash, the group collected pools of three Indian currency values (10, 20, 100), suspended the notes in DNA extraction buffer for 10-12 hours, and extracted/sequenced the DNA.
|A figure from the paper, showing the distribution of|
microbes found on money. (Figure 2A)
Moving on from asking "what microbes are present?" to "what are they doing?", the group looked at the functional potential of the microbes found on the notes. They did do a general survey of all of the genes present, but this is pretty abstract and difficult for us to sink our teeth into. As a nice specific investigation, the group looked at the antibiotic resistance genes present on the notes. Their sequencing approach, as well as PCR validation to those genes, revealed 78 potential antibiotic resistance genes. While this is interesting and further highlights a source of antibiotic gene resistance transfer in our environment and culture, it is so important to take this with a grain of salt because these are only potential antibiotic resistance genes.
In the end, what can we say about this paper? There are two main points you should leave with. First is that the microbial communities of money are primarily environmental eukaryotes including algae, with a much smaller fraction being bacteria. In retrospect, this makes sense because our money is constantly in contact with the environment, so it seems to pick up the environmental DNA. The second point is that money harbors potential antibiotic resistance genes, which suggests it could play a role in transmitting antibiotic resistance. While this does not mean your cash will give you a terrible, antibiotic resistant infection (or at least it is highly unlikely), it does highlight currency as another means of pathogenic gene transfer.
You still don't need a lab safety suit to handle
your cash. <SOURCE>
So what does all of this mean for your life? Honestly not a whole lot. Out of our own experiences, we intuitively know money can be dirty, and this paper further supports that by telling us more about how dirty it is. But next time you pay for something, think about the bacteria, eukaryotes, and other microbes that bill left behind on your hands and in your wallet. This is pretty cool stuff.
Jalali S, Kohli S, Latka C, Bhatia S, Vellarikal SK, Sivasubbu S, Scaria V, & Ramachandran S (2015). Screening currency notes for microbial pathogens and antibiotic resistance genes using a shotgun metagenomic approach. PloS one, 10 (6) PMID: 26035208