Kinetic Aspects Of The Bioconversion Of 4-Chlorobenzoate To 4-Hydroxybenzoate By Alcaligenes Denitrificans Ntb-1 Immobilized In Carrageenan

Abstract

Alcaligenes denitrificans NTB-1 converts 4-chlorobenzoate to 4-hydroxybenzoate by means of a hydrolytic dehalogenation. In the presence of oxygen the product is further metabolized by the cells. Although it has been shown that the dehalogenation does not require oxygen, no bioproduction of 4-hydroxybenzoate was achieved by whole cells when oxygen was absent. An energy-dependent active transport may explain this anomaly. Little activity was lost after immobilization of whole cells in carrageenan. Diffusion of oxygen within the carrageenan beads rapidly limited the rate of decolorization. This effect was magnified with increasing bead diameters and cell loadings. External transport of oxygen, on the other hand, did not decrease the reaction rate, except at extremely low oxygen concentrations. Maximal dehalogenation activity was observed at 35°C and at pH 8.0 and this was independent of whether free or immobilized cells were used. 4-Hydroxybenzoate significantly inhibited the rate of decolorization, while the chloride formed and the substrate 4-chlorobenzoate did not show inhibitory effects on decolorization. The yield of this bioconversion was mainly dependent on the oxygen concentration. In the case of free cells, 4-hydroxybenzoate was produced only at very low oxygen concentrations, while immobilized cells still produced 4-hydroybenzoate at air saturation as a result of oxygen diffusion limitation.

Key Words:

• Bioconversion
• 4-chlorobenzoate dehalogenation
• 4-hydroxybenzoate formation
• immobilized
• Alcaligenes
• carrageenan.