The mammalian microbiota plays a crucial role in the pathogenesis of many diseases. Thanks to recent advances in metagenomics, proteomics, and metabolomics, microbiome composition and metabolic activity can now be studied in detail. Results obtained by such fascinating and provocative studies would be meaningless without considering the perspective of the whole organism. Our work using gnotobiology as the major tool to unravel the mechanisms of host-microbe interaction has demonstrated the crucial role of microbiota in the initiation and progression of inflammation-associated colorectal neoplasia. Carcinogenesis in the gut is driven by the presence of potentially harmful microbes or by lack of protective ones, by the production of carcinogens generated by microbes, and by the induction of inflammation and modulation of the immune system. Here, we review these mechanisms with special emphasis on those where gnotobiology has yielded important insights.

From the *Institute of Microbiology Academy of Sciences of the Czech Republic Prague and Novy Hradek Czech Republic; † 1st Faculty of Medicine Institute of Immunology and Microbiology Charles University Prague Prague Czech Republic; and ‡Department of Pathology Immunology and Laboratory Medicine College of Medicine University of Florida Gainesville FL

References provided by Crossref.org

Colorectal Tumour Mucosa Microbiome Is Enriched in Oral Pathogens and Defines Three Subtypes That Correlate with Markers of Tumour Progression

Spontaneous and Induced Tumors in Germ-Free Animals: A General Review

Oral Bacterial and Fungal Microbiome Impacts Colorectal Carcinogenesis

Gnotobiotic mouse model's contribution to understanding host-pathogen interactions