Effects of Soil Matric Suction on Retention and Percolation of Bacillus Subtilis in Intact Soil Cores

Abstract

Bacillus subtilis endospores (resistant to rifampicin) irrigated on the surface of intact soil cores (20 cm diameter × 8 cm length) which were equilibrated under selected suctions, i.e. 0, 0.5, 2, 5, 10 kPa, were then percolated by saturated water flow. The bacterial retention and percolation percentage were significantly correlated with the suctions. The higher retention with higher suction was explained by micropore storage, attachment to static air-water interface (AWI), and irreversible adsorption to soil particles. The bacterial percolation was mainly controlled by initial replacement of pore water storage, and following reversible detachment process. Another sensitivity experiment with four replicates using lincomycin-resistant B. subtilis at 0 and 0.5 kPa suctions revealed that small increase (0 to 0.5 kPa) in soil matric suction incurred a substantial higher level of bacterial retention. Based on our experimental results, soil matric suction was proposed as a comprehensive parameter to monitor bacterial transport and fate for animal waste disposal (irrigation) and subsurface bioremediation.