WITHDRAWN: Nitrogen sources enhance siderophore-mediated competition for iron between potato common scab and late blight causative agents

Abstract

How do pathogens colonizing the same host interact with each other? We evaluated here the types of interactions taking place between Streptomyces scabiei and Phytophthora infestans, the causative agents of common scab and late blight diseases on potato crops, respectively. Under most conditions tested S. scabiei impaired or completely inhibited the growth of P. infestans by producing either soluble and/or volatile compounds. Media component analysis revealed that increasing peptone levels correlated with increased inhibition of P. infestans. Comparative metabolomics showed that production of S. scabiei siderophores (desferrioxamines, pyochelin, scabichelin and turgichelin) increased with the quantity of peptone thereby suggesting that they participate in the inhibition of the oomycete growth. Mass spectrometry imaging further uncovered that the zones of secreted siderophores and of P. infestans growth inhibition coincided. Moreover, either the repression of siderophore production or the neutralization of the iron-chelating activity of siderophores both led to a resumption of P. infestans growth. Importantly, replacement of peptone by natural nitrogen sources such as sodium nitrate, ammonium sulfate, and urea also triggered siderophore production in S. scabiei. Overall, our work further emphasizes the importance of competition for iron between microorganisms that colonize the same niche. As common scab never alters the biological function of tubers, we propose that S. scabiei, under certain conditions, could play a protective role for its hosts against much more destructive pathogens through exploitative iron competition and volatile compound production.