Effect of Humic Fractions and Clay on Biodegradation of Phenanthrene by a Pseudomonas fluorescens Strain Isolated from Soil

The mineralization of phenanthrene in pure cultures of a Pseudomonas fluorescens strain, isolated from soil, was measured in the presence of soil humic fractions and montmorillonite. Humic acid and clay, either separately or in combination, shortened the acclimation phase. A higher mineralization rate was measured in treatments with humic acid at 100 μg/ml. Humic acid at 10 μg/ml stimulated the transformation only in the presence of 10 g of clay per liter. We suggest that sorption of phenanthrene to these soil components may result in a higher concentration of substrate in the vicinity of the bacterial cells and therefore may increase its bioavailability.