Special issue: The Human Intestinal Microbiota.

The human intestine is home to very large numbers of micro-organisms, with bacterial cells exceeding 10 ml in the colon. The impact that this complex community has upon the host is increasingly recognized not only as a potential source of infection but also as a contributor to nutrient and energy supply, gut development and immune homeostasis. Recent evidence has indicated links between gut microbial activities and the aetiology of disorders such as inflammatory bowel disease and colorectal cancer, and also conditions such as heart disease, diabetes and metabolic syndrome. All this makes a special issue of Microbiology devoted to the human intestinal microbiota timely. This topic necessarily depends heavily on microbial ecology, a discipline that has not always been natural territory for the journal, notwithstanding some important contributions to human intestinal microbiology (e.g. Macfarlane et al., 1986). Molecular methodologies have done much to accelerate recent progress by allowing the rapid analysis of this complex community, culminating in the application of in-depth metagenomics (Qin et al., 2010). Nevertheless, the commonly perceived wisdom that most human intestinal bacteria are inherently unculturable may not be entirely accurate, since many of the most common intestinal bacteria found by molecular methods in faecal samples correspond to cultured species of obligate anaerobes (Walker et al., 2010). The future, in which the journal can play an important role, will surely require a combination of genomics, microbial ecology and studies of single cultured organisms.