Microecology A midsummer bug hunt
D EPENDING ON WHERE you live, June 21st is either the summer or the winter solstice. For some, this is a moment of celebration, accompanied by strange rituals. And among the celebrants are members of the International Metagenomics and Metadesign of Subways and Urban Biomes Consortium (MetaSUB). If, in Bogotá, Doha, Kuala Lumpur, London, Minneapolis or any other of some 60 cities around the world, you see on that day someone furtively swabbing a ticket counter, handrail, turnstile or seat in your local underground-railway station, be not afraid. It is just one of MetaSUB’s volunteers gathering samples of the local microbes.
MetaSUB’s purpose is to understand the invisible complexes of bacteria, archaea, fungi and viruses that are life’s smallest representatives. Every year, on June 21st, it co-ordinates an army of small-game hunters who have the task of sampling their city’s public transport. The swabs are then tagged with time of collection, local temperature and humidity, and the nature of the sampled surface, and sent off for genetic sequencing and statistical analysis.
The consortium’s latest findings, published recently in Cell, are based on 4,728 samples collected in 2015, 2016 and 2017. These show that each city has a microbial ecosystem distinctive enough (see chart) to serve as a fingerprint. An algorithm trained on the data could identify the origin of a randomly chosen sample 88% of the time. A few species are ubiquitous. Thirty-one (all bacteria) were found on almost every swab, and a further 1,145 (also, bar brewers’ yeast, bacteria) turned up in over 70% of samples. The vast majority of the 4,246 identifiable species were, however, much more narrowly distributed.
