WATER-FACILITATED TRANSPORT OF BACTERIA IN UNSATURATED SOIL COLUMNS - INFLUENCE OF CELL-SURFACE HYDROPHOBICITY AND SOIL PROPERTIES

The numbers of bacteria, surface applied to soil columns which were subsequently irrigated, decreased exponentially with depth. The numbers of surface-inoculated bacteria decreased by a factor of 10 every 1.1-6.0 cm of soil depth after irrigating the columns with 5 cm of water at a rate of 2.5 cm h-1. Major differences were observed between the examined test strains. The migration of hydrophobic strains was 2-3 times slower compared to that of hydrophilic strains. This was correlated with an increased adhesion of the hydrophobic strains to soil particles. Increasing the bulk density of the soil from 1.27 to 1.37 g cm-3 reduced the volume of the pores with a diameter of 16-30 mum by ca 80%. This corresponded with a decrease in the migration of bacteria by 30-60%. Migration was reduced by ca 40-80% in a sandy soil mixed with 20% clay soil. The reduction was more pronounced for hydrophilic bacteria.