Prokaryotic and eukaryotic diversity of the human gut.

The human intestinal tract is one of the most densely populated ecosystems studied to date. Recently, the gut microbiota have been implicated as an environmental factor in health and disease; however, as with all ecosystems, a significant proportion of these microbiota are as yet uncultured. Hence culture-independent molecular-based methods have been applied and have started to provide insights into the microbes in this system. This review explores the recent significant findings in the last 5 years in the area of gut microbial ecology. Most significant is the observation that the gut microbiota are dominated by species from the phyla Firmicutes and Bacteroidetes. Regardless of whether first- or second-generation sequencing technologies are used to explore the microbial diversity, these two phyla are found throughout the intestinal tract, with other microbes such as the viruses and micro-eukayrotes, which, while being present, are either in low numbers or have not received much attention. Simply put, the Firmicutes and Bacteroidetes have made the gut their own, and the next stage in the study of this fascinating system will be to establish the roles they play in the host's health.