Characterization of Gordonia sp. strain CC-NAPH129-6 capable of naphthalene degradation

A naphthalene-degrading isolate able to utilize naphthalene as a sole carbon source was identified as Gordonia sp. CC-NAPH129-6. Here a detail characterization of the naphthalene catabolic genes present in this strain was conducted. In nar region four structural genes (narAa, narAb, narB, narC), two regulatory genes (narR1, narR2), a rubredoxin encoding gene (rub1) and a gene (orf7) with unknown function were obtained. When compared with most of the members within naphthalene-degrading Rhodococcus, these naphthalene catabolic genes in strain CC-NAPH129-6 were organized into an operon-like gene cluster and present in the same order. This naphthalene gene cluster located in a 97-kb small plasmid of strain CC-NAPH129-6, as can be seen from the PFGE and Southern blot hybridization data. Besides, a partial transposase sequence containing an IS element structure with 12-nt inverted repeat at both ends was found, which was flanked by direct repeats downstream the narC gene in strain CC-NAPH129-6. This novel transposase gene sequence was unlike to the transposase sequence found between narR2 and rub1 genes in Rhodococcus opacus R7. The comparative analyses of the naphthalene catabolic genes, 16S rRNA and gyrB gene present in strain CC-NAPH129-6 and naphthalene-degrading Rhodococcus species imply that the naphthalene catabolic genes in strain CC-NAPH129-6 might be horizontally transferred from Rhodococcus members. This is the first report demonstrating that naphthalene catabolic genes organized into an operon-like gene cluster in the genus Gordonia, and this might provide evidence of the importance of this actinobacterial lineage in the bioremediation of oil-contaminated soils.