Sphingomonas yanoikuyae strain B1 is able to degrade a wider range of aromatic hydrocarbons than S. paucimobilis strain TNE12 can degrade. Various culture techniques were used to corroborate that B1 used m-xylene, biphenyl, toluene, naphthalene, and phenanthrene as sole carbon and energy sources. In contrast, TNE12 could not mineralize m-xylene, biphenyl, toluene, or naphthalene. However, fluoranthene served as carbon and energy source for TNE12 but not B1. Southern blots were performed using the cloned genomic region (approximately 23 kb) containing the degradative genes for the upstream pathways for biphenyl and in-xylene and a TOL plasmid-type meta operon from B1 as a probe against the KpnI restriction-digested total DNA of TNE12. This 23 kb probe hybridized to three KpnI-digested fragments of TNE12 DNA; thus significant homology existed between the aromatic hydrocarbon-degrading genes of B1 and TNE12. Further work with smaller probes revealed, however, that TNE12 DNA fragments did not hybridize with the probe containing the genes encoding for xylene monooxygenase and part of an aromatic dioxygenase. A recombinant plasmid, which contains only the genes for xylene monooxygenase, is able to complement TNE12 on m-xylene. These genes are, therefore, probably missing from TNE12. Hence, TNE12 cannot use monocyclic aromatics whereas B1 can. Pulsed field gel electrophoresis coupled with Southern blotting revealed that the aromatic degradative genes were on an approximately 240 kb plasmid of TNE12; the same genes in B1 are known to be chromosomal.
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Acknowledgments This research was supported in part by an appointment of EK to the Postgraduate Research Program at the National Center for Toxicological Research through an interagency agreement between the U.S. Department of Energy and the U.S. Food and Drug Administration and a grant from Yonsei University. The authors would like to thank Bruce Erickson and Ashraf Khan for critical review of the manuscript.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology