A Synthetic Biology Approach to Combat Fungal Infections

Candida albicans is the most prevalent human fungal pathogen causing life-threatening infections in individuals with an impaired immune system. In most cases, systemic infections arise from endogenous sources like the intestine, where C. albicans can be found as normal member of the gut flora. However, upon certain triggers the fungus can switch from a yeast-like growth form to filamentous growth, penetrate the intestinal mucosa and cause severe systemic infections, which are associated with high mortality rates in part due to difficulties in rapid diagnosis. The triggers for the transition from the non-pathogenic to the pathogenic form of C. albicans remains poorly understood. Prophylaxis with antifungal drugs is currently used to avoid systemic infections. This, however, can promote an increase in resistant fungal strains. Thus, novel strategies to counteract invasive fungal infections are needed. The main hypothesis of this fellowship application proposes the use of reprogrammed gut bacteria as prophylaxis against C. albicans infections. A synthetic biology approach will be used to develop bacterial strains able to sense the fungus in the intestine, bind to it and produce filamentation inhibitors thereby preventing mucosal invasion and systemic infection. To enable sensing of C. albicans, bacterial promoters, which are activated in the presence of the fungus, will be identified in a screening approach. These promoters will be used to control the expression of the Streptococcus gordonii SspB protein, which will facilitate bacterial-fungal interaction. Furthermore, identified promoters will be coupled to a filamentation-inhibition module enabling bacterial cells to produce filamentation inhibitors, thereby blocking mucosal penetration. The developed system will be tested in vitro during interaction with mucosal cells as well as in vivo in a mouse infection model. The use of reprogrammed bacteria as prophylaxis against fungal infections represents a novel strategy with great potential in the future. Furthermore, the system described in this proposal will also serve as a highly valuable tool to study the transition from the non-pathogenic to a pathogenic form of C. albicans, as well as the interaction of bacterial and fungal species with the host.

Candida albicans is the most prevalent human fungal pathogen causing life-threatening infections in individuals with an impaired immune system. In most cases, systemic infections arise from endogenous sources like the intestine, where C. albicans can be found as normal member of the gut flora. However, upon certain triggers the fungus can switch from a yeast-like growth form to filamentous growth, penetrate the intestinal mucosa and cause severe systemic infections, which are associated with high mortality rates in part due to difficulties in rapid diagnosis. The triggers for the transition from the non-pathogenic to the pathogenic form of C. albicans remains poorly understood. Prophylaxis with antifungal drugs is currently used to avoid systemic infections. This, however, can promote an increase in resistant fungal strains. Thus, novel strategies to counteract invasive fungal infections are needed. The main hypothesis of this project proposed the use of reprogrammed gut bacteria as prophylaxis against C. albicans infections. A synthetic biology approach has been used to develop bacterial strains able to sense the fungus and respond by producing a filamentation inhibitor thereby preventing host cell damage and mucosal invasion. To enable sensing of the fungus, a novel substance produced by C. albicans has been discovered and used to create a bacterial sensor. Furthermore, the developed sensor has been coupled to a filamentation-inhibition module enabling bacterial cells to produce a filamentation inhibitor, thereby blocking damage of host cells by C. albicans. The developed system was successfully tested in vitro during interaction with mucosal cells. The use of reprogrammed bacteria as prophylaxis against fungal infections represents a novel strategy with great potential in the future. Furthermore, the sense-and-respond system developed in this project will also serve as a highly valuable tool to study the transition from the non-pathogenic to a pathogenic form of C. albicans, as well as the interaction of bacterial and fungal species with the host.