Cellobiose transport: the key to trigger virulence in the plant pathogenic bacterium Streptomyces scabies
J. SALAZAR (1), S. Jourdan (2), M. Kim (3), S. Rigali (2), R. Loria (3), I. Francis (1,3) (1) California State University Bakersfield, U.S.A.; (2) University of Liège, Belgium; (3) University of Florida, U.S.A

The phytotoxin thaxtomin A, the main virulence determinant of the pathogens Streptomyces scabies, S. acidiscabies and S. turgidiscabies, affects the plant cell wall by interfering with cellulose synthase leading to stunted growth, cell hypertrophy and tissue necrosis. Cellobiose, a subunit of the plant cell wall polymer cellulose, has been shown to trigger thaxtomin production. Based on homology searches, two gene clusters were identified in the genome of S. scabies. One cluster is highly conserved among streptomycetes, while the other cluster is present in S. scabies. Specific deletion mutants were evaluated to elucidate the role of these transporters in the S. scabies pathology. Our results demonstrate that cellobiose transport and not sensing is required for the induction of thaxtomin biosynthesis and thus virulence. While one transporter was shown to be the actual cellobiose-specific transporter, inactivation of the second transporter did not impair toxin production in the presence of cellobiose. However, under more complex conditions, as would be in plant-microbe interactions, the loss of this transporter could not be compensated for by the first transporter as shown by the results of plant bioassays and the inability of this mutant to produce toxin in plant-based media. Furthermore, our work highlights how genes associated with primary metabolism in nonpathogenic Streptomyces species have been recruited as elements of virulence in plant pathogenic species.

Abstract Number: P7-169
Session Type: Poster