Kunming Institute of Zoology, Chinese Academy of Sciences

Despite the prevalence of colorectal cancer (CRC) around the world in general and China in particular, relatively little is known about the underlying causal mechanisms of CRC. Current research that has attempted to find novel risk factors for these disorders suggests that alongside the traditional risks of dietary, genetic, and environmental factors, bacterial infections may play a significant role in CRC. Previous reports observed that several infectious bacteria, including Fusobacterium spp., Bacteroides fragilis, and Escherichia coli—all of which are widely distributed throughout China—are connected with a higher risk of CRC in several different populations across the globe. These findings prompted ZHANG Zhigang and GENG Jiawei of the Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences (CAS) to investigate if connections between CRC and bacteria in the gut microbiome may be a common phenomenon or may even have specific patterns among different populations.　

In collaboration with researchers at the First People’s Hospital of Yunnan’s Department of Gastroenterology, ZHANG’s team evaluated eight Chinese patients, comparing their cancerous and healthy gut tissues to see if there was a higher prevalence and pattern to some of the hypothesized infectious bacterial agents. Using pyrosequencing-based molecular monitoring of bacterial 16S rRNA genes, they were able to analyze and describe the basic features of the CRC-associated microbiome.

ZHANG’s team discovered a surprising diversity in the tumor-associated bacterial communities. In half of the Chinese patients they studied, there were significant increases in Roseburia and a concurrent decrease of both Microbacterium and Anoxybacillus in the cancerous tissue. This novel pattern of over-represented Roseburia at tumor sites and similarly over-represented Microbacterium and Anoxybacillus away from tumor sites was closely related in Chinese patients suffering from CRC, illustrating a novel pattern of bacterial communities among Han Chinese.

When comparing their findings to previous studies done on other populations, like the French and the Dutch, ZHANG’s team noted that two factors traditionally considered to be strongly involved in risk for CRC—diet and genetics—might play less of a role than previously thought in CRC and these kind of bacterial infections. The differentiation of Roseburia for CRC among Chinese was consistent between the Chinese and the Dutch, two populations with large dietary and genetic differences. ZHANG’s team concluded that the potential role of Roseburia as a passenger bacteria should s examined much more thoroughly in occurrences of CRC across all populations

ZHANG’s findings of a new population-specific pattern of bacterial communities associated with CRC in the gut provides researchers a preliminary understanding of bacterial links to CRC and paving the way for individual and population-specific treatments. While the discoveries made in this study are just the beginning in exploring a deeper and more complete picture of the role bacteria in the gut microbiome of patients with CRC, these findings highlight the need to constantly approach how we view human disease risk factors in a new light, as well as the potential gains we can make in borrowing from both high-throughput meta-genomic or transcriptomic data and (animal) model experiments to more fully understand human disease pathogenesis.