The developmental journey from birth, through infancy, childhood and into adulthood is a complex one, not least for the trillions of bacteria residing in our gut, the so-called gut microbiome. The gut microbiota is a highly complex community which evolves and adapts to its host over a lifetime and is integral to the health of its host, serving a myriad of functions, from providing essential nutrients, prevention of pathogen colonisation, immune functioning to interactions within the brain through the gut-brain microbiome axis. The study of the gut microbiome has been revolutionised over the last 15 years by advances in genetic methods and sophisticated bioinformatic tools. Next generation sequencing (NGS) is a low-cost, high-throughput sequencing platform that enables analysis of all the genomes within an ecosystem sample (shotgun metagenomics), or a description of the taxa within a given community by sequencing conserved marker genes such as the 16srRNA gene of bacteria and archaea. We have been interested for a number of years in studying the gut microbiome in early life and uncovering the plethora of factors that impact the bacteria an infant acquires at birth and in early life. In this study, we sequenced DNA from faecal samples of children over the first four years and found that there is a perpetual evolution of the gut microbiota during this period.

The origin of the eukaryotic cell represents one of the most fundamental mysteries in the evolution of cellular life on Earth. Already in the beginning of the 20th century, several researchers and cell biologists noticed the resemblance of mitochondria and chloroplasts to free-living bacteria, an observation that shaped the basis for various subsequently formulated endosymbiotic theories, which suggest that eukaryotic organelles are derived from bacterial symbionts. Throughout the years, various detailed models have been proposed to account for the partners involved as well as the processes underlying this symbiosis (Lopez-Garcia and Moreira, 2015; Lopez-Garcia et al., 2017; Martin et al., 2017). Yet, while the identity of the ancestors of mitochondria and chloroplasts could be ascribed to alpha-proteobacteria and cyanobacteria, respectively, the nature of the host cell remained an enigma for several decades.