Deep sequencing and functional analyses identify a role of Fusobacterium species in colorectal tumorigenesis

The tumor microenvironment is a complex community consisting of neoplastic cells, surrounding stromal cells, a broad array of immune cells, and a microbiota. By sheer numbers, the microbiota has its greatest manifestation in colorectal cancer (CRC) because the colon contains up to 100 trillion bacteria, outnumbering human cells by a factor of 10 and encoding a gene-content that is 100-fold larger than that of the human genome. Indeed, previous studies using germ-free mice in a variety of genetic backgrounds have demonstrated that the microbiota can impact colorectal tumorigenesis. In addition, specific strains of enterotoxigenic bacteria have been shown to promote colitis-associated cancer in mice. Here, we explore the composition of the tissue-associated microbiota in human CRC and evaluate the role of tumor-enriched microbes in potentiating colorectal tumorigenesis in mice.