Abstract A07: The involvement of a type VII secretion system in the interactions between Streptococcus gallolyticus subspecies gallolyticus and colorectal cancer

Colorectal cancer (CRC) is the 2nd-3rd most common cancer worldwide and is a leading cause of cancer-related death. Increasing evidence suggests that the gut microbiome plays an important role in the development of CRC. One such organism of the gut microbiome that plays an important role in CRC is Streptococcus gallolyticus subspecies gallolyticus (Sgg). Previously, we reported that Sgg stimulates CRC cell proliferation in a β-catenin dependent manner. Using an azoxymethane-induced mouse model of CRC, we have also shown that Sgg-treated mice had significantly higher tumor burden in the colon compared to mice treated with saline or negative control bacteria, suggesting that Sgg actively promotes the development of CRC. The mechanism underlying Sgg’s role in CRC development, however, has yet to be elucidated. The type VII secretion system (T7SS), also called the Esx secretion system, is a specialized secretion system found primarily in Firmicutes and Actinobacteria and has been shown to play an important role in virulence in Staphylococcus aureus and Mycobacterium tuberculosis. Here, we examined the genome of Sgg and found that it encodes a putative T7SS (SggT7SS) highly similar to the T7SS in S. aureus with respect to sequence identity and gene organization. We further showed that the SggT7SS is functional. To investigate if the SggT7SS is involved in the connection between Sgg and CRC, we generated an Sgg mutant lacking the core components of the T7SS secretion machinery. Functional characterization of the mutant indicates that SggT7SS is intimately involved in the interactions between Sgg and CRC cells. Taken together, our results suggest that a T7SS system may be important in inducing specific host responses to Sgg in the context of CRC. Studies to further elucidate the activities of T7SS and its role in Sgg’s contribution to CRC are currently under way. Citation Format: John Culver Taylor, Jacob Rutherford, Maria Nunez, Yi Xu. The involvement of a type VII secretion system in the interactions between Streptococcus gallolyticus subspecies gallolyticus and colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr A07.