Degradation of low concentrations of dichlorobenzenes and 1,2,4-trichlorobenzene byPseudomonassp. strain P51 in nonsterile soil columns

Abstract

A newly isolated Pseudomonas species, strain P51, growing aerobically on all dichlorobenzene isomers and on 1,2,4-trichlorobenzene as sole carbon and energy sources was tested for its ability to mineralize these components also in a non-sterile soil environment. Untreated sand from the river Rhine in which none of the dichloro- and trichlorobenzenes were degraded was placed in a percolation column and inoculated with Pseudomonas sp. strain P51. The column was fed continuously with synthetic river water containing the chlorinated compounds at concentrations between 10 μg/1 and 1 mg/1. The inoculated microorganisms were able to degrade the chlorinated benzenes and survived for at least 60 days in the column. For each compound a specific threshold concentration was observed below which no further degradation took place, and which was independent of the initial concentration. These threshold were 6 ± 4 μg/1 for 1,2-dichlorobenzene, 20 ± 5 μg/1 for 1,2,4-trichlorobenzene and more than 20 μg/1 for the 1,3- and 1,4-isomers. Repeated inoculation of the column with strain P51 did not affect this minimal concentration. In noninoculated soil columns the native microbial population adapted to degrade 1,2-dichlorobenzene after a long lag phase, and reduced it from 25 μg/1 to a threshold concentration of 0.1 μg/1.