SPHINGOMONAS SP HV3 HAS A NOVEL SET OF OPERONS FOR CATABOLISM OF AROMATICS

Kim Yrjälä, Lars Paulin, and Martin Romantschuk.

Department of Biosciences and Institute of Biotechnology, University of Helsinki

P.O. Box 56, Biocenter 1C, FIN-00014 University of Helsinki

Sphingomonas bacteria have been found to be important in biodegradation of xenobiotics. We have studied the function of the pSKY4 Sphingomonas sp. HV3. degradative plasmid in degradation of aromatics. Sphingomonas sp. HV3 was isolated in the late 1970's from Finnish field soil as a herbicide degrading strain. It was classified as a Pseudomonas species. A detailed taxonomic study revealed recently that strain HV3 is a Sphingomonas species. The cmp- plasmid-encoded aromatic pathway of HV3 is very similar to the chromosomal pathway from Sphingomonas yanoikuyae. The gene organization is also very similar to the unpublished plasmid-encoded pathway of Sphingomonas aromaticivorans which was isolated from deep subsurface soil. Catabolic pathways have only been described in these three Sphingomonas species. It appears that the aromatic-degrading Sphingomonas bacteria may have a common pathway for biodegradation of aromatics. The novel aspect in these pathways is that different kinds of aromatics such as xylenes, polyaromates and biphenyls appear to be degraded through the same complex pathway which is either chromosomal or plasmid-encoded. Sphingomonas sp.HV3 does not degrade xylenes and biphenyls like S. yanoikuyae and S. aromaticivorans. It is therefore of interest to find out how the pathways differ in gene structure and encoded proteins.

S. aromaticivorans might be considered as a more ancient type of the Sphingomonas bacteria since it is isolated from deep subsurface soil carrying a less evolved degradative plasmid pNL1. The surface soil S. yanoikuyae in turn can be thought of as a more evolved soil bacterium with its chromosomal pathway. In this context Sphingomonas sp. HV3 is an interesting surface soil bacterium with a plasmid-encoded pathway which has been subjected to selective and changing conditions in Finnish field soil. Comparison of these bacteria give valuable evolutionary insights of this novel aromatic pathway.