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Streptomyces bacteria from soil often produce antibiotics which inhibit growth of other microbes. When comparing Streptomyces’ inhibitory ability between different soils, it may be important to match the pH of the medium used in assays to the pH of the soil they came from. We assayed Streptomyces isolates collected from a long-term agricultural experiment with nitrogen-fertilized and non-fertilized treatments to determine their ability to inhibit growth of other bacteria by producing antibiotics. Average soil pH was 6.8 in fertilized soil and 7.2 in non-fertilized soil. We dotted isolates on a glucose-asparagine agar medium adjusted to different pH values and overlaid them with a non-pathogenic Streptomyces standard to measure their inhibitory ability. Some isolates produced different inhibition zone sizes depending on medium pH. However, response to assay medium pH did not differ significantly among isolates from soils of different pH. More tests are needed to determine whether it is necessary to match the medium pH to the pH of the soil the isolates came from when comparing prevalence of antibiotic production among Streptomyces from different soils

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Streptomyces; Soil microbiology; Bacterial growth


Bacteriology | Environmental Microbiology and Microbial Ecology | Food Science

Effect of Assay Medium pH on Inhibitory Ability of <i>Streptomyces</i>