SOIL AGGREGATION BY STREPTOMYCES BACTERIA

Experiments were conducted to assess the potential for Streptomyces bacteria to aggregate soil. Soil microbes known to stabilize soils are abundant and have filamentous growth habits that allow for enmeshing soil particles. Streptomyces exhibit both characteristics. Soil aggregation is an important ecosystem function provided by some soil microbes. Well aggregated soils hold more air and water, resist erosion, and sequester large amounts of carbon. The purpose of this study was to observe and quantify the ability of 4 Streptomyces strains to create soil aggregates from unstructured soil. Soil was crushed to 500 pm particles and half was sterilized before being mixed with an equal mass of unsterilized crushed soil, and then inoculated with Streptomyces. Controls were treated with sterile growth medium, and 5 replicates were set up for each treatment. After inoculation and incubation, the samples were dried and measured for aggregation. This was done by placing the samples in a set of 4 sieves of decreasing mesh size which were submerged in a pail of water. The sieves were agitated, and the soil particles settled until trapped in a given sieve. The total mass of aggregates on each sieve was used to calculate the amount of aggregation compared to the controls to determine the effectiveness of each strain. The data were analyzed using an ANOVA with treatment as the factor. Half of the isolates examined significantly increased the size of the aggregates produced over 4 weeks (F9,56 = 8.5, p