Isolation Of Tetrabromobisphenol A (TBBPA) Degradation Bacteria From Anaerobic Sludge And The Degradation Characteristics

Tetrabromobisphenol A (TBBPA) is widely used in the world with the increasing accumulation in various environmental media. TBBPA has been demonstrated to cause adverse effects on environment and biosome because of its refractory, biological migration and accumulation. The notoxic transformation of TBBPA in the environment is going to be a hot area of research with more and more attentions. Biodegradation is more economical and efficacious than the other degradation technologies for the mineralization of TBBPA. After acclimatization, the bactiera capable of degrading TBBPA were isolated from anaerobic sludge obtained from a sewage treatment plant in Nanjing, China. The optimal degradation conditions including temperature and pH were investigated. The biodegradation pathway and the fate of the metabolites were speculated.The process of acclimatization was completed in a reactor. In order to ensure a stable acclimatization conditions, the reactor, shaking at 180 r/min, was controlled at 30℃ and pH 6.8-7.0. After 100 days of acclimatization, the microorganisms in the reactor were able to degrade TBBPA effectively in 10 days. The degradation rates were 94.8%.Two different TBBPA degradation bacteria were isolated from the anaerobic sludge after isolation and purification, named as NJUST20 and NJUST21. Both of them were able to degrade TBBPA at 30℃ and pH 7.0. The degradation rates of NJUST20 and NJUST21 were 62.85% and 42.28%, respectively, with the initial TBBPA concentration of 10 mg/L,6 days later.The colonies of strain NJUST20 were yellowish white with regularly edges and concave, smooth, glossy surfaces.3 days later, the diameters of the colonies were about 2-4 mm. The colonies of strain NJUST21 were opaque and somewhat iridescent. The edges were not clear and surfaces were dendritic. Both of them were gram negative bacteria. The cells of strain NJUST20 were straight rods in shape and about 0.61×(1.33-1.57) μm in size and peritrichous under SEM. While strain NJUST21 were nearly spherical short rods. Size of cells was about 0.59×(0.64-0.93)μm. Strains NJUST20 and NJUST21 were identified as Enterobacter sp. and Serratia sp. based on the 16S rDNA analysis, repectively. The names Enterobacter sp. NJUST20 and Serratia sp. NJUST21 were proposed. Comparison of the characteristics between NJUST20 and the species of the genus Enterobacter showed that NJUST20 was closer to Enterobacter gergoviae.Strain NJUST20 was chosed because of the higher TBBPA degradation rate. The results of single factor experiments indicated that the optimum conditions for strain NJUST20 were 35℃ and pH 7.0.6 days later, the residual TBBPA and the degradation rate were 1.8 mg/L and 81.9%, respectively. The degradation process fit the first order model. The degradation rate constant (k) and degradation half-live (T1/2) was found to be 0.4020 d-1 and 1.6 d, respectively. On basis of the metabolites identification and previous reports, the pathway for the metabolism of TBBPA by strain NJUST20 was proposed as:TBBPA was initially converted as BPA by losing four bromine atoms. Subsequently, BPA was transformed into 2,4-dihydroxyacetophenone and 2,5-dihydroxybenzoic acid.2,4-dihydroxyacetophenone may be transformed as 2,4-dihydroxybenzoic acid. After that,2,5-dihydroxybenzoic acid and 2,4-dihydroxybenzoic acid were further degraded as 4-hydroxy-5-methyl-2-hexanone. The end metabolites were oxalic acid and isobutyric acid, which were nontoxic and could be used by microorganisms directly.This work is promising for the remediation of environmental media contaminated by TBBPA. It’s significant for the completely mineralization of TBBPA under anaerobic conditions and the development of the engineering bacteria for TBBPA degradation. Moreover, we provide a useful reference for the investigation of TBBPA biodegradation pathways and degradation conditions in anaerobic.