Aerobic biodegradation of diphenylamine

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Kim, Jenny Gi Yae
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Diphenylamine (DPA) is a primary pollutant used as a stabilizer and as precursor for pesticides, pharmaceutical products and dyes. It has recently been found that a dioxygenase enzyme is responsible for the ability of bacteria to biodegrade diphenylamine (8). Despite our understanding of the degradation pathway of DPA, important questions remain regarding the evolutionary origin of the gene that encodes the dioxygenase. The answers to these questions will help future efforts to biodegrade this hazardous pollutant. Through selective enrichment, isolation and genetic screening, aniline degrading bacteria have been discovered to be responsible for the genes that encode the lower part of the DPA degradation pathway. Using the same technique of enrichment, isolation and genetic sequencing, we screened for candidates for the origin of the genes that encode DPA dioxygenase. Our hypothesis is that carbazole dioxygenase is the progenitor of DPA dioxygenase at the Repauno site. Comparison of the dioxygenase genes will allow us to test the hypothesis that horizontal gene transfer facilitated assembly of the pathway. We have also hypothesized that DPA degrading bacteria will not be able to degrade carbazole as a sole carbon, nitrogen and energy source to determine whether or not degrading bacteria are capable of having two pathways of degradation. We will test DPA degraders to determine whether or not they are able to degrade carbazole. Analyzing carbazole degradation will allow us to test the hypothesis that DPA degrading bacteria will not have retained the ability to degrade carbazole during the evolution of DPA dioxygenase due to our hypothesis that DPA dioxygenase originated from carbazole dioxygenase. In our future studies we are hoping that a carbazole degrader will encode a carbazole dioxygenase that will show significant similarities to DPA dioxygenase. We hope to develop results what will suggest that the dioxygenase gene originated from carbazole degraders through horizontal gene transfer. Experiments revealed that carbazole was not degraded by DPA degraders. The data support our hypothesis that DPA degrading bacteria did not retain the carbazole degradation pathway from carbazole degrading bacteria during the evolution of DPA dioxygenase.
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