Construction of a Hybrid Pathway for Selectively Removing Nitrogen Atom from Carbazole

Acid precipitation resulting from oil combustion has driven enormous efforts to remove sulfur and nitrogen contaminants from fossil fuels, including biological treatment as alternatives. Unlike biodesulfurization where sulfur is selectively removed from substrates leaving the hydrocarbon portion of the molecule intact, the pathway of carbazole (typical nitrogen compound in oils) degradation only liberates nitrogen in the course of completely degrading the substrates, leading a loss of the oil combustion values. While there have been no publications concerning pathway engineering to investigate the selective removal of nitrogen atom from carbazole. In the native pathway, carbazole was firstly metabolized into 2’-aminobiphenyl-2,3-diol catalyzed by carbazole 1,9a-dioxygenase. A novel deaminase from chloronitrobenzene degradation is expected to be evolved, which could selectively remove amino-group from 2’-aminobiphenyl-2,3-diol. Combination of the carbazole 1,9a-dioxygenase and the evolved deaminase, a ‘hybrid’ pathway for carbazole metabolism is proposed, in which carbazole should be selectively transformed into hydroxylated biphenyl. The synthetic pathway will be capable of simultaneously and selectively removing nitrogen atom to retain the carbon skeleton of the fuels and therefore keep the combustion values.