Pseudomonas Spp. can Inhibit Streptomyces scabies Growth and Repress the Expression of Genes Involved in Pathogenesis

Abstract

Common scab, caused by Streptomyces scabies, is an economically important disease affecting potato crops world- wide. Con fi rmed and putative pathogenicity- and virulence-related factors, including the phytotoxic thaxtomins, the necrosis protein Nec1 and the tomatinase TomA, have been characterized in S. scabies. Using plate inhibition assays, the ability of three antimicrobial metabolite-producing Pseudomonas strains (LBUM 223, LBUM 300 and LBUM 647) to inhibit the growth of S. scabies was studied. Their capacity to alter the expression of thaxtomin biosynthesis genes ( txtA and txtC ), nec1 and tomA was also investigated using newly developed TaqMan probe-based quantitative reverse transcription-polymerase chain reaction assays. Pseudomonas sp. LBUM 223 signi fi cantly inhibited S. scabies growth and repressed transcription of all targeted genes in the pathogen. S. scabies growth was also signi fi cantly inhibited by Pseudomonas sp. LBUM 300; however, this strain failed to alter the expression of any of the targeted genes. Finally, Pseudomonas sp. LBUM 647 was unsuccessful both at inhibiting pathogen growth and at repressing gene transcription in S. scabies. To our knowledge, this is the fi rst demonstration that an antagonistic organism can repress the expression of key genes involved in S. scabies pathogenesis. This capacity is unlikely a trait common to all Pseudomonas spp.