ABSTRACT
Microbes are the oldest and, at the same time, most abundant living organisms, having existed for almost four billion years. Although eukaryotic protists, the pioneer metazoans, and the earliest plants were surely around much earlier, it was not until about 550–600 million years ago that the massive evolution of multicellular animal and plant species occurred. It is perhaps unsurprising that microbes remain the dominant life form on our planet, since the explosion of multicellular life provided a huge and abundant diversity of environments for bacteria to colonize. Microbes display a wide diversity of specialized interactions with eukaryotic organisms.
