Nature's microbiome: introduction

In recent years, it has become common knowledge that we, and the many organisms around us, are symbiotic crea- tures, harbouring large numbers of internal and external microbial residents. Research on symbiosis has progressed remarkably since the days of van Leeuwenhoek and de Bary, whose discoveries paved the way for over two centuries of fascinating work. Indeed, since their findings on bacteria in human mouths and algal-fungal partnerships that constitute lichens, we have discovered that microbial symbionts have shaped the make-up of the eukaryotic cell and that they continue to influence growth, development, energy metabolism, nutrition, digestion and defence of eukaryotes from across the globe (Wernegreen 2012; McFall-Ngai et al. 2013). It is now widely understood that microbial symbionts are important sources of innovation across eukaryotes, making symbiosis one of the hallmarks of eukaryotic biology.