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Title:   Author  item
                                            DAVELOS, ANITA - UNIVERSITY OF MINNESOTAitem
                                            KINKEL, LINDA - UNIVERSITY OF MINNESOTAitem
                                            Samac, Deborah

                                                         - *Debby*
  Submitted to: Applied and Environmental Microbiology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/19/2003
                                    Publication  Date: 2/1/2004
                                    Citation: Davelos, A.L., Kinkel, L.L., Samac, D.A. 2004. Spatial variation in the frequency and intensity of antibiotic interactions among streptomycetes from prairie soil. Applied and Environmental Microbiology. 70(2):1051-1058.Interpretive Summary: Antibiotic-producing microorganisms are common in most soils. The antibiotics most likely give the producing microorganism a competitive advantage. Antibiotics also play a central role in the management of many diseases of animals and plants. The majority of known antibiotics are made by Streptomycete bacteria. Several Streptomycetes are used to control plant tdiseases. Despite their importance, little is known about the ecology of antibiotic-producing microorganisms in soil or on factors that lead to development of antibiotic production and antibiotic resistance in soil communities. In this study, Streptomycetes were isolated from 3 locations and 4 depths in a prairie soil and tested for their ability to produce antibiotics and resist antibiotics produced by other Streptomycetes. Among the 162 isolates tested, the ability to resist antibiotics was more common than the ability to produce antibiotics. Resistance was found at similar  rates in all locations and depths. This suggests that antibiotic resistanc confers a greater benefit than antibiotic production or may be less costly to maintain. The Streptomycetes producing antibiotics were very diverse and were found at higher rates at lower soil depths suggesting a greater amount of competition lower in soil. Most of the isolates that produced antibiotics were not the same isolates that were resistant to antibiotics. These results indicate that the factors leading to antibiotic production by Streptomycetes are distinct from those leading to antibiotic resistance. Understanding the ecology of Streptomycetes in native soils will aid in developing strategies for using Streptomycetes to control plant diseases in agricultural soils. Development of such biological controls will give growers more choices for ecologically sound crop production.
                                Technical Abstract: The production of antibiotics may increase the fitness of micro-organisms by providing them a competitive advantage. Furthermore, the spatial distribution of antibiotic-producing and non-producing microbes is likely to influence ecological interactions among soil micro-organisms. Indeed, antibiotic activities of indigenous microbes have been implicated in the  development of disease suppressive soils and may play a role in pathogen inhibition in non-agricultural systems. However, little is known of the frequency, intensity, and diversity of antibiotic inhibition and resistance among indigenous microbes in prairie soil. The ability of Streptomyces isolates from prairie soil to inhibit growth and resist antibiotics produced by 10 standard Streptomyces isolates from a disease-suppressive soil was examined. Wide variation in antibiotic inhibition and resistance for individual isolates among 3 locations and 4 soil depths within a 1 m2  plot was revealed. Fewer than 10% of isolates could inhibit or resist all 10 standards. One-third of isolates were unable to inhibit any of the standards while no isolate was susceptible to all of the standards. The frequency and intensity of inhibition of the standards by indigenous Streptomyces isolates differed among locations and tended to increase with increasing depth of isolation. Resistance was more common than inhibition and had a fairly stable frequency across locations and depth. No correlation between inhibition and resistance phenotypes was found, indicating that inhibition and resistance may be under independent selection. Antibiotic activities may be highly clustered in space and might be structured by a variety of competitive interactions.


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