Propachlor removal by Pseudomonas strain GCH1 in an immobilized-cell system

Abstract

A bacterial strain capable of growing on propachlor (2-chloro-N-isopropylacetanilide) was isolated from soil by using enrichment and isolation techniques. The strain isolated, designated GCH1, was classified as a member of the genus Pseudomonas. Washed-cell suspensions of strain GCH1 accumulated N-isopropylacetanilide, acetanilide, acetamide, and catechol. Pseudomonas strain GCH1 grew on propachlor with a generation time of 4.2 h and a rate of substrate utilization of 1.75 +/- 0.15 micromol h(-1). Gene expression did not require induction but was subject to catabolite expression. Acetanilide was a growth substrate with a yield of 0.56 +/- 0.02 mg of protein micromol(-1). GCH1 strain cells were immobilized by adsorption onto a ceramic support and were used as biocatalysts in an immobilized cell system. Propachlor elimination reached 98%, with a retention time of 3 h and an initial organic load of 0.5 mM propachlor. The viability of immobilized cells increased 34-fold after 120 days of bioreactor operation.

FIG. 1

Schematic of reactor for immobilized cell in ceramic support. (a and b) Scanning electron micrographs of immobilized GCH1 cells adsorbed onto the surface of the ceramic support, 48 h (a) and 360 h (b) after inoculation. (c and d) Laser scanning confocal micrographs showing viable cells after 60 days (c) and 120 days (d) of reactor operation. (e to g) Viability cell evolution during 150 days of reactor operation.

FIG. 2

Growth of Pseudomonas strain GCH1 in batch culture with propachlor as the carbon source. Shown are the metabolic intermediates identified by GC-MS analysis as described in Materials and Methods.

FIG. 3

Results obtained from operation of the bioreactor treating synthetic wastewater. (A) Removal of propachlor from the wastewater expressed as percentage of initial propachlor concentration. (B) Kinetics of propachlor degradation. The results are the averages of a three-cycle operation run.