The Study On Degradation Of Biphenyl And Derivates By Rhodococcus Sp. R04

In today's world, the increasingly serious environmental problems have become the world topics of concern to people. However, among many of methods for pollutant treatment, one of most efficient and popular is biological treatment method, which is economic, efficient, especially, not produce secondary pollution. It is found that the microorganisms play an important role in the bioremediation. Rhodococcus is one of them, which can not only degrade many halogenated biphenyls, hydrocarbons, lignin, coal, but also petroleum and other substances.This paper firstly researched the degradated ability to polychlorinated biphenyls, polybrominated and fluoride biphenyl by Rhodococcus sp. R04 via HPLC. Three influencing factors, including different substituted elements, numbers and position of substituted elements were investigated to correlate structural features to degradation of polyhalogenated biphenyls by Rhodococcus sp. R04. The results showed, for mono-substituents, the degradation preference of R. sp. R04 were in the order 4-FB>4-CB≥4-MB>4-BrB. When the substituted elements were same, the degradation rates of halogenated biphenyls reduced as halogen substitution increased. This strain was relatively insensitive to the halogen substitution pattern on the biophenyl ring, when halogenated biphenyls containing the same halogen substitution and numbers, the effect of the position of substituted halogen on the degradation of polyhalogenated biphenyls was great, especially 2,6-CB, which intensively showed striking resistance to degradation, eventually led to the reduction of degradation rates.The yellow cleavage products (YCP), which were produced in the aerobic metabolism of polyhalogenated biphenyls, were measured by spectroscopy and HPLC. The results indicate that polyhalogenated biphenyls were degraded in the oxidation open-loop degradation pathway, thus YCPs act as a biomarker during the degradation of polyhalogenated biphenyls. YCP accumulation inevitably blocks the degradation pathway of polyhalogenated biphenyl. Furthermore, this paper investigated the transformation of the yellow cleavage products by the laccase. The results showed that the laccase can transform the yellow cleavage products, and the degradation ability was different due to the different halogenated biphenyl. The laccase have a strong degradation ability towards the intermediate metabolites of 4-FB,4,4'-FB, and 4-CB, which could be faded completely in the shorter time by 0.045 U of laccase. For the yellow cleavage products of 3,4-CB and 4-MB, the degradation ability is relatively weak, the yellow can be faded completely after 60 min at room temperature by 0.045 U of laccase; The transformation of yellow cleavage products of 2,4',5-CB, which can not be transform by R04 is further reduced after 9 hours by 0.45 U of laccase.Moreover, we investigated the degradation of DBT by Rhodococcus sp. R04 and its mutant strains whose genes relative to PCB degradation were knocked out. The results showed that Rhodococcus sp. R04 preincubated in the basal medium containing biphenyl can degrade DBT, and it can be almost completely degraded after three days; however, its mutant strain (ΔA,ΔB,ΔC,ΔD) can not degrade DBT, so we suggest that the bph gene cluster is responsible for not only biphenyl degradation but also DBT degradation in the strain R04.