Abstract
Biphenyl dioxygenase is one of the Rieske-type oxygenases, which catalyze the insertion of oxygen into the aromatic ring, and is produced in chemoheterotrophic bacteria that have ability to degrade biphenyl and congeners of polychlorinated biphenyl (PCBs). Comamonas testosteroni strains YAZ2 and YU14-111 are gram-negative and rod-shaped aerobic bacteria that are newly isolated from the soil from Yonezawa. They can utilize biphenyl as a sole carbon energy source and can degrade PCBs effectively. Meanwhile, microbubbles with diameters less than 100 μm are receiving attention because of their properties such as large surface area per unit volume, low rising velocity, and self-pressurization due to surface tension. Using microbubbles can make the solubility of oxygen improved in comparison with conventional bubble contactors. Here, we present that the biphenyl dioxygenase over-expressed bacterial formulations of C. testosteroni strains highly degraded PCBs when the solution for catalyzing reaction was saturated with oxygen by ultrasonically generated microbubbles. The degradation rate of PCBs by the YU14-111 formulation with oxygen microbubbles increased up to 8% compared to that without the microbubbles. Furthermore, the time-dependent PCB degradation by the YAZ2 formulation also resulted in increased degradation rate up to 15.1% in 48hrs with oxygen microbubbles compared to that without microbubbles. These data suggest that the ultrasonically generated microbubble with oxygen up-modulates the catalytic activity of the PCB-degrading bacterial formulation regardless of the strains.
