Study: Microbial companions are highly specialised

Zoologists at the University of Basel have demonstrated that microbial communities on humans and animals are largely dominated by specialists.

Whilst humans and other mammals are often hosts to several thousand species, and even minute organisms like water fleas which can carry over one hundred species, the initial question by the researchers was how specialised these microbes are. Most bacteria only get recruited after their hosts’ birth and it would assumed that most of them are generalists, with microbes able to live in different environments and on a variety of hosts having a significant advantage over specialists.

Backed by funding from the European Research Council, the scientists, led by Dieter Ebert, hypothesised that the successful microbes are specialists, meaning that the successful species are those that prefer one specific host, where they then occur locally in great numbers. To test their thesis they developed a statistical method allowing them to align the relative abundance of a specific bacteria species with the degree of its local specificity.

With this new method, the researchers analysed data from three very different sources: zooplankton from the Ägelsee in Frauenfeld (Switzerland), different habitats on the people (including ear, nose, mouth and armpit), and a set of diverse ecosystems, including water and sediment samples from fresh water and from the sea.

All three data sets revelaved that locally abundant microbes are local specialists and conversely, the smaller the relative abundance of one species, the more likely is it found in several habitats. Generalists are everywhere but nowhere in abundance, whereas specialists only occur in significant numbers locally.

The full results are published in the journal Ecology Letters.