Characterization of a ring-hydroxylating dioxygenase from phenanthrene-degrading Sphingomonas sp. strain LH128 able to oxidize benz[a]anthracene
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Sphingomonas sp. strain LH128 was isolated from a polycyclic aromatic hydrocarbon (PAH)-contaminated soil using phenanthrene as the sole source of carbon and energy. A dioxygenase complex, phnA1fA2f, encoding the α and β subunit of a terminal dioxygenase responsible for the initial attack on PAHs, was identified and isolated from this strain. PhnA1f showed 98%, 78%, and 78% identity to the α subunit of PAH dioxygenase from Novosphingobium aromaticivorans strain F199, Sphingomonas sp. strain CHY-1, and Sphingobium yanoikuyae strain B1, respectively. When overexpressed in Escherichia coli, PhnA1fA2f was able to oxidize low-molecular-weight PAHs, chlorinated biphenyls, dibenzo-p-dioxin, and the high-molecular-weight PAHs benz[a]anthracene, chrysene, and pyrene. The action of PhnA1fA2f on benz[a]anthracene produced two benz[a]anthracene dihydrodiols.
KeywordsBioremediation Meta-cleavage operon genes Indigo formation Rieske nonheme iron oxygenase
L.S. gratefully acknowledges the Fund for the Promotion of Research in Industry and Agriculture (F.R.I.A.), Belgium, for providing a doctoral fellowship. L.S. also wishes to thank the members of the Unit of Physiological Biochemistry (FYSA), Catholic University of Louvain, for their daily help and constructive remarks for many years. PH is a research associate at the Belgian National Fund for Scientific Research (FNRS).
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