Nutrient-Dependent Efficacy of the Antifungal Protein YvgO Correlates to Cellular Proliferation Rate in Candida albicans 3153A and Byssochlamys fulva H25

YvgO is a recently characterized antifungal protein isolated from Bacillus thuringiensis SF361 that exhibits a broad spectrum of activity and pH stability. Customized colorimetric metabolic assays based on standard broth microdilution techniques were used to determine the variable tolerance of Byssochlamys fulva H25 and Candida albicans 3153A to YvgO exposure under select matrix conditions impacting cellular proliferation. Normalization of the solution pH after antifungal challenge expanded the available pH range under consideration allowing for a comprehensive in vitro assessment of YvgO efficacy. Indicator susceptibility was examined across an array of elementary growth-modifying conditions, including media pH, incubation temperature, ionic strength, and carbohydrate supplementation. Under suboptimal temperature and pH conditions, the indicator growth rate reduced, and YvgO-mediated susceptibility was attenuated. While YvgO association but not efficacy was somewhat influenced by solution ionic strength, carbohydrate supplementation was shown to be the most influential susceptibility factor, particularly for C. albicans. Although the specific choice of carbohydrate/nutrient supplement dictated the extent of enhanced YvgO efficacy, D-glucose additionally improved the association between antifungal and target. Indeed, when exposed to YvgO under conditions that lead to increased cellular proliferation, both indicators displayed a stronger association and susceptibility to YvgO when compared to carbohydrate-deprived media or suboptimal incubation environments. With further study, YvgO may have the capacity to function as a prophylaxis for food safety and preservation, as well as a pharmaceutical agent against opportunistic fungal pathogens either independently or in combination with other established treatments applied to both livestock and human health concerns.