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1 Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
2 Department of Microbiology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
3 Department of Industrial Chemistry, Faculty of Engineering, Shibaura Institute of Technology, 3-9-14 Shibaura, Minato-ku, Tokyo 108-8548, Japan
Correspondence
Hiroshi Habe
hiroshi.habe{at}aist.go.jp
Sphingomonas sp. strain A4 is capable of utilizing acenaphthene as its sole carbon and energy source. To isolate the genes responsible for acenaphthene degradation, transposon mutagenesis was performed on strain A4 and four mini-Tn5-inserted mutants lacking the ability to utilize acenaphthene were isolated. In three of the four mini-Tn5 inserted mutants, the mini-Tn5s were inserted into the same locus (within about 16 kb) as the arhA1A2 genes, which had previously been identified as the genes encoding the terminal oxygenase components for the initial oxygenation of acenaphthene. The nucleotide sequence analysis of the corresponding 16.4 kb DNA fragment revealed the existence of 16 ORFs and a partial ORF. From these ORFs, the genes encoding the ferredoxin (ArhA3) and ferredoxin reductase (ArhA4) complementary to ArhA1A2 were identified. RT-PCR analysis suggested that a 13.5 kb gene cluster, consisting of 13 ORFs and including all the arhA genes, forms an operon, although it includes several ORFs that are apparently unnecessary for acenaphthene degradation. Furthermore, using gene disruption and quantitative RT-PCR analyses, the LysR-type activator, ArhR, required for expression of the 13.5 kb gene cluster was also identified. Transcription of the gene cluster by ArhR was induced in the presence of acenaphthene (or its metabolite), and a putative binding site (T-N11-A motif) for ArhR was found upstream from the transcription start point of arhA3.
The GenBank/EMBL/DDBJ accession number for the sequence of the arh genes and their flanking regions reported in this paper is AB240454.
Present address: National Institute of Advanced Industrial Science and Technology (AIST), Central 5-2, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan.
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