W731 Interspecies Signaling Interactions and Pathogen Suppression Among Soilborne Streptomyces

Date: Sunday, January 15, 2012
Time: 9:40 AM
Room: Pacific Salon 2
Linda L. Kinkel , Department of Plant Pathology, University of Minnesota, Saint Paul, MN
Patricia Vaz , Department of Plant Pathology, University of Minnesota, Saint Paul, MN
Christine Salomon , Center for Drug Design, University of Minnesota, Minneapolis, MN
In Streptomyces, diverse signaling compounds have been suggested to provide a highly specific means for mediating antibiotic production.  However, little empirical work has explored the frequency of signaling, the complexity of signaling networks, the possible effects of signaling on pathogen suppressive activity of Streptomyces communities, or the diversity of signaling compounds within individual communities in soil. We explored pairwise inhibitory and signaling interactions and phylogenetic relatedness (16S rRNA) among Streptomyces in soil.  Thirty Streptomyces were isolated from 3 soil microcores within a Midwestern U.S. prairie.  Antibiotic inhibition (mean zone size) and signaling were determined among all possible combinations from within and among cores.  Plates were coinoculated with Streptomyces isolates growing 1 cm apart.  After 3 d, a target Bacillus was overlaid and after 24 h, inhibition zones were measured.  Signaling was evaluated as any significant increase or decrease in inhibitory zone size induced by the presence of another isolate. Induction or repression of antibiotic production occurred in 38% of 870 isolate combinations.  The frequency of signaling was significantly higher among isolates from the same than from different soil cores, suggesting local selection for signaling among coexisting Streptomyces.  The impacts of signaling on antibiotic production varied among locations:  isolates from 2 locations had consistently enhanced antibiotic production in the presence of another isolate, while isolates from the third location exhibited consistent repression of antibiotic production.  Collectively, these data suggest that interspecies signaling is likely to have a significant effect on Streptomyces phenotypes and, consequently, on pathogen suppression in soil.