Special issue: The Human Intestinal Microbiota.

in the colon. The impact that this complex community hasupon the host is increasingly recognized not only as apotential source of infection but also as a contributor tonutrient and energy supply, gut development and immunehomeostasis. Recent evidence has indicated links betweengut microbial activities and the aetiology of disorders suchas inflammatory bowel disease and colorectal cancer, andalso conditions such as heart disease, diabetes andmetabolic syndrome. All this makes a special issue ofMicrobiology devoted to the human intestinal microbiotatimely. This topic necessarily depends heavily on microbialecology, a discipline that has not always been naturalterritory for the journal, notwithstanding some importantcontributions to human intestinal microbiology (e.g.Macfarlane et al., 1986). Molecular methodologies havedone much to accelerate recent progress by allowing therapid analysis of this complex community, culminating inthe application of in-depth metagenomics (Qin et al.,2010). Nevertheless, the commonly perceived wisdom thatmost human intestinal bacteria are inherently unculturablemay not be entirely accurate, since many of the mostcommon intestinal bacteria found by molecular methodsin faecal samples correspond to cultured species of obligateanaerobes (Walker et al., 2010). The future, in which thejournal can play an important role, will surely require acombination of genomics, microbial ecology and studies ofsingle cultured organisms.Four reviews in this special issue deal with the role of thehuman gut microbiota in irritable bowel syndrome(Salonen et al., 2010), the metabolism of dietary phyto-chemicals (Kemperman et al., 2010), interactions ofprobiotic bacteria with the gut mucosa (Sa´nchez et al.,2010) and the impact of long-term antibiotic use on thegut microbial community (Jernberg et al., 2010). Theimpact of a new antibiotic upon the intestinal communityof Clostridium difficile-infected patients is reported byTannock et al. (2010). The diversity of the intestinalcommunity is explored by Roger & McCartney (2010) andby Roger et al. (2010) in infants, by Rajilic´-Stojanovic´ et al.(2010) in an in vitro intestinal model system and byContreras et al. (2010) in the oral cavity of Amerindians.Interactions of intestinal bacteria with the mammalianimmune system are considered by Knoch et al. (2010) forthe microbial community of the caeca of interleukin-10gene-deficient mice, and by Donato et al. (2010) for aprobiotic strain of Lactobacillus rhamnosus. Probiotic andprebiotic approaches are of course aimed at manipulatingthe intestinal microbial community and host responses toachieve health benefits. Penders et al. (2010) explorethe possible relationship between lactobacilli and allergy,while O’Flaherty & Klaenhammer (2010) report on aLactobacillus acidophilus surface protein, and MacKenzieet al. (2010) on mucin-binding proteins of Lactobacillusreuteri. Bifidobacteria are most commonly chosen astargets for prebiotics, and understanding of this group isadvanced by a comparative genomic study by Bottaciniet al. (2010). An informative study using an in vitrofermenter model (Zihler et al., 2010), however, illustratesthe difficulty of predicting the impact of prebiotics andprobiotics on complex microbial communities. Finally, onepaper focuses on an obligate anaerobe, examining thecapsular polysaccharides of Bacteroides fragilis (Patricket al., 2010). We would like to thank all the authors who responded tothe call for manuscripts to be considered for this specialissue, and to all the reviewers and editors involved inprocessing these papers. This has resulted in a valuableand varied set of contributions that provide a snapshot ofthe rapid progress taking place in this topical field. Wefirmly believe that Microbiology can make an increasinglyvaluable contribution to this field in the future bypublishing quality papers on the ecology, physiology andgenetics of micro-organisms that inhabit the humanintestinal tract.