Non-indigenous endospore persistence following release in a snow–soil system

Knowledge of snow–soil–microbial interactions could lead to the development of strategies that exploit snow as a delivery system for microorganisms to soil or for nutrients that would in turn influence the soil microbiota. A predictable soil–snow–microbial system could promote or sustain native or introduced microbial activity during periods of snow cover or preserve and preposition viable but inactive microorganisms until conditions become favorable for growth. Knowledge of these manipulations could result in strategies to target desired soil microbial processes. Potential applications include bioremediation and decontamination. We hypothesized that population dynamics at the snow–soil interface would be a determinant in the growth and survival of an introduced species and that the microbial community would not be static. Using replicated field studies, we characterized native microbial populations in a local soil with and without snow cover using molecular-based taxonomic methods. We introduced the bacterial species Bacillus thuringiensis to the soil prior to snowfall and to the snow covering following snowfall. As competition, we also added Pseudomonas syringae to the snow in selected treatments. During a single winter and into the spring, we periodically sampled the snow–soil interface to characterize the prevailing microbial populations. Results showed that micro-eukaryotes, either protists or fungi, increased significantly under snow. P. syringae survival and growth was detected for up to 80 days post-inoculation to snow. B. thuringiensis, added as endospores, remained and survived mainly in the endospore state.