Streptomyces scabiei, only a plant pathogen? Understanding the antagonism between Streptomyces scabiei and Phytophthora infestans

Abstract

So far, the study of the interaction between potato phytopathogens and their host has primarily focused on their virulence determinants and their infection mechanisms. In this study, our aim is to understand the interactions between two pathogens (Streptomyces scabiei and Phytophthora infestans) that infect the same plant host (Solanum tuberosum). A prior study illustrated the antagonistic effects of S. scabiei 87-22 against P. infestans. The inhibition increased proportionally to the amount of peptone added in the medium. A comparative metabolomic study revealed that desferrioxamines (siderophores) are suggested to be the best candidates responsible for this antagonism. The first objective of this master’s thesis is to identify the molecules by which S. scabiei inhibits the growth of P. infestans and determine whether this characteristic is also shared by other members of the Streptomyces genus. The second objective is to unveil the environmental elicitors that trigger the production of these antagonistic compounds. Main results: Through our experiments to answer the first question, we demonstrated that by targeting iron homeostasis (by depleting or replenishing the media with iron), we could modulate the growth inhibition of P. infestans, meaning that siderophores play a key role in this antagonism by competing for this essential nutrient, thus depriving P. infestans and inhibiting its growth. We also observed that this strategy was widespread amongst Streptomyces species. To achieve the second objective, we substituted peptone (a nitrogen source used for synthetic media preparations in labs) with nitrogen sources commonly used for soil amendment in agriculture. We demonstrated that nitrogen sources triggered the production of siderophores and induced growth inhibition of P. infestans. However, the mechanism by which nitrogen sources control siderophore production remains unknown.