DEGRADATION OF CHLOROANILINES BY IMMOBILIZED ​ACINETOBACTER BAUMANNII STRAIN GFJ1

Abstract

Chloroanilines are aromatic amines, which have been widely used as ingredients for chemical production including pesticides, dyes and several pharmaceuticals. They are also generated from natural transformation of several herbicides applied into agricultural areas. Thus, they are widely detected in environment, especially in water. Because they are toxic to human and other living organisms and are included in the priority pollutant list, the treatment of these pollutants is necessary. In this study, Acinetobacter baumannii strain GFJ1 isolated from soil was the first pure culture showing its biodegradation ability towards mono-, di- and trichloroanilines as growth substrates. A. baumannii GFJ1 is the first reported bacterial strain that utilized CAs as sources of sole carbon, nitrogen and energy under both aerobic and anaerobic conditions. The determination of the aerobic utilization profile showed that the utilization kinetics followed the Edward model. Under anaerobic conditions, 42.0 ± 4.5% and 32.2 ± 8.5% of 0.1 mM 4CA, and 44.2 ± 0.2% and 28.0 ± 0.3% of 0.1 mM 34DCA were utilized as a growth substrate by A. baumannii GFJ1 with nitrate and sulfate as electron acceptors, respectively, after 20 days. However, the anaerobic utilization of 4CA and 34DCA was significantly lower than that under aerobic conditions. The determination of degradation pathway in A. baumannii GFJ1 showed that the bacteria strain transformed 34DCA to 3CA, 3CA and 4CA was degraded via a modified ortho-cleavage pathway. The 34DCA degradation rates and growth rates of A. baumannii GFJ1 immobilized in beads were significantly higher than freely suspended cells. To enhance the biodegradation rates and mass transfer in the polyvinyl alcohol (PVA)–alginate matrix, pore-forming agents (progens) was used in cell immobilization processes. The addition of CaCO3 and polyethylene glycol (PEG) as porogens into carriers resulted in the changes of bacterial activities. The bead with 10% PVA, 2% alginate and 5% porogen achieved the highest biodegradation rates with 93.6% ± 2.8% of 34DCA degraded after 12 hours, and growth rates among the various tests with different CaCO3 and PEG concentrations. It was found that the addition of the porogens into the carriers increased diffusion coefficient, porosity, pore size and swelling ratio of carriers. The addition of cryopotectants into immobilized gels enhanced cell tolerance during freeze-drying and storage. Among cryoprotectants, glycerol incorporation could effectively sustain 34DCA biodegradation of entrapped cells after 1-month storage at room temperature. The determination of biodegradation of entrapped cells and characterizations of the carrier would provide a method for the design and optimization of the carrier for cell immobilization.