Ph.D. Student Penn State University Park, Pennsylvania
Body of Abstract: Plant-produced resources could affect microbial activity and microbial composition in the soil. Compared to the sparse resources available in the soil, plant roots release sugar and metabolites. We hypothesize that this spatial gradient of resources corresponds to a gradient of low to high microbial activity spanning the soil-rhizosphere-endosphere compartments. To test this, we used BONCAT (Bioorthogonal Non-Canonical Amino Acid Tagging) to measure microbial activity in-situ across the soil-rhizosphere-endosphere gradient. After two months of growth, we incubated plants for 24 hours with a methionine analog (HPG- L-Homopropargylglycine) and sampled microbes from the rhizosphere, and nodules. We clicked the HPG to a fluorescent probe making the translationally active cells fluorescent. We used FACS (fluorescence-activated cell sorting) to count the number of active fluorescent cells over total extracted cells and collected cells for 16S rRNA sequencing. We found a higher absolute number of active cells in the rhizosphere than in bulk soil. As we predicted, microbial activity was higher in the plant fractions (endosphere and nodule) than in both soil fractions (rhizosphere and soil) ( >10% to 1%, respectively). These results confirmed our hypothesis and aligned with previous studies that had demonstrated increased microbial activity in the rhizosphere using other activity probing techniques. Our 16S rRNA sequencing of the active microbial community revealed differential community composition between active and inactive microbial communities and across the soil-rhizosphere-endosphere compartments. Our implementation of BONCAT in the rhizosphere and root tissues opens the door to understanding plant-driven selection in the soil microbial community.