Sorry there’s not been many posts for a while. I entered a poonami. For those of you without children, that’s a technical biology term for when you’ve just finished changing one nappy (American: ‘diaper’) only to have another spurt out. You understand me…

But it did get me thinking again (my poor, post-partum, sleep-deprived brain) about metagenomics of human mucosa. I wondered: okay, so we’ve started to look in depth at the microbial community composition of different parts of the gut, and variations both between individuals and over time: but what about the skin? Surely there’s as much variation there – I mean the environmental exposure ought to guarantee a healthy number of arrivals, if nothing else? And what about the meeting-areas (yes, I was looking at a bum covered in nappy-rash at the time, as I said)?

Turns out this week’s seen a really tidy paper published that starts to answer this question (see also Patrick Schloss’ comment in the same issue). In Nature, Julia Oh and colleagues present a fascinating metagenomic analysis of multiple skin sites (18: including gems such as the ‘earhole’, ‘crotch’ and, mmmm, ‘toenail’) and critically, individuals. I say ‘critically’ because the comparison between individuals lets them pool data to see, in effect, whether variance at skin sites is nested among individual and/or whether, say, an armpit swab is an armpit swab is an armpit swab, if you look at two individuals or two thousand (a cheering thought).

Excitingly, they see big differences in the community compositions between skin sampling locations, both in terms of kingdom (bacteria/viruses/eukaryotes) and more granular scales of organisation – and some of these differences vary by individual, others not. With more data-driven (OK, you might say ‘fishing’) experiments like this it’s tempting to underplay results like this: the finding that, well, microbial communities are variable might not seem that unexpected. Well, it isn’t: but that doesn’t mean we should ignore the fact that this is vastly more interesting than the obvious null hypothesis, e.g: if all skin everywhere on the body looks the same and feels the same to us, the simplest expectation would be that the communities are composed similarly too. Instead this research raises all sorts of questions – obviously related to pathogenicity and disease risks / burdens – but also more interesting biological ones, such as: does gene flow occur between these sites? Is composition vertically influenced by your parents’ microbial metagenome? And so on. And there’s a hefty data set published to look at as well.

Unfortunately, in answer to the questions ‘do some poos sting a raw bum more than others?’ and ‘how can I prevent a poonami?’ require further research at this point…