Comparison of Phenolic Substrate Utilization and Growth Kinetics Between Immobilized and Suspended Degradative-Bacteria

Improving dioxygenase stability by gene chromosome insertion: implementation in immobilized-cell systems

The immobilization of recombinant cells by using the unstable 3,4-dihydroxyphenylacetate 2,3-dioxygenase was studied as a model. Dioxygenase activity and cell viability were compared in immobilized-cell systems and cells in suspension. Immobilization increased enzyme stability and the efficient degradation of 3,4-dihydroxyphenylacetate. The stability of the cloned enzyme and the viability of the immobilized recombinant cells were well maintained for at least 15 days. We used the strain Escherichia coli CC118-D in which the hpaB gene from Klebsiella pneumoniae, coding for the subunit of 3,4-dihydroxyphenylacetate 2,3-dioxygenase, was inserted into the chromosome. This study has demonstrated that the implementation of E. coli CC118-D in a pilot-scale bioreactor resulted in a 100% stabilization of dioxygenase activity, and could be a useful tool for bioremediation processes.

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

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.