Isolation and Characterization of Agrobacterium Strains from Soil: A Laboratory Capstone Experience†

In this investigation, the students' goal was to isolate and characterize Agrobacterium strains from soil. Following selection and enrichment on 1A-t medium, putative Agrobacterium isolates were characterized by Gram stain reaction and biochemical tests. Isolates were further evaluated using polymerase chain reaction (PCR) with different primer sets designed to amplify specific regions of bacterial deoxyribonucleic acid (DNA). Primer sets included AGRH to identify isolates that were members of the Rhizobiaceae, BIOVAR1 primers to identify members of Agrobacterium biovar group I, and a third set, VIRG, to determine presence of virG (only present in pathogenic Agrobacterium strains). During the investigation, students applied previously learned techniques including serial dilution, use of selective/differential media, staining protocols, biochemical analysis, molecular analysis via PCR, and electrophoresis. Students also gained practical experience using photo documentation to record data for an eventual mock journal publication of the capstone laboratory experience. Pre- and post-evaluation of class content knowledge related to the techniques, protocols, and learning objectives of these laboratories revealed significant learning gains in the content areas of Agrobacterium-plant interactions (p ≤ 0.001) and molecular biology (p ≤ 0.01). The capstone journal assignment served as the assessment tool to evaluate mastery and application of laboratory technique, the ability to accurately collect and evaluate data, and critical thinking skills associated with experimental troubleshooting and extrapolation. Analysis of journal reports following the capstone experience showed significant improvement in assignment scores (p ≤ 0.0001) and attainment of capstone experience learning outcomes.