Naphthalene catabolic plasmid

Austen RA, NW Dunn (1980) Regulation of the plasmid-specified naphthalene catabolic pathway of Pseudomonas putida. J Gen Microbiol 117 521-528. 

Stuart-Keil KG, AM Hohnstock, KP Drees, JB Herrick, EL Madsen (1998) Plasmids responsible for horizontal transfer of naphthalene catabolism genes between bacteria at a coal tar-contaminated site are homologous to pDTGl from Pseudomonas putida NCIB 9816-4. Appl Environ Microbiol 64 3633-3640. 

Dunn NW, HM Dunn, RA Austen (1980) Evidence for the existence of two catabolic plasmids coding for the degradation of naphthalene. J Gen Microbiol 117 529-533. 

The naphthalene catabolic genes are located in most cases on plasmids. In this group the best-studied plasmid is NAH7 of P. putida PpG7. It carries two operons, one of which enables the utilization of naphthalene and the other salicylate. Both operons are turned on by the product of another NAH7 gene, nahR, in the presence... 

Fernandez, M., Niqui-Arroyo, J.L., Conde, S., Ramos, J.L., and Duque, E. (2012) Enhanced tolerance to naphthalene and enhanced rhizoremediation performance for Pseudomonas putida KT2440 via the NAH7 catabolic plasmid. Appl. Environ. Microbiol., 78 (15), 5104-5110. 

The reactions, described so far, are derived from tiie most extensively studied catabolic pathway for naphthalene, which is encoded by the NAH7 plasmid of Pseudomonas putida. But, the same sequence of reactions seems to take place in all naphthalene-degrading bacteria, which means that salicylate is a common intmmiediate in naphthalene catabolism. With respect to the enzymes involved in the breakdown of naphthalene, there seem to exist differences between the bacterial species, that can grow on naphtiialene-containing media. A recently isolated and described Rhodococcus sp., for example, seems to have a 1,2-dihydroxynaphthalene oxygenase that requires NADH [38]. 

Figure 2. A) Genetic organization of the pKAl catabolic plasmid. Genes of the upper naphthalene regulatory system encode for proteins that mediate the conversion of naphthalene to salicylate. Salicylate is then further degraded to TCA cycle intermediates. B) In Pseudomonas fluorescens HK44, genes within the lower pathway were replaced with genes of the lux cassette to produce a bioluminescent bioreporter sensitive to naphthalene and salicylate.

The plasmids and operons described above represent the most studied ones, but probably constitute a small fraction of the catabolic operons in bacteria. In one study, 43 bacterial strains (mostly Pseudomonas spp.) from different sources, shown to possess the ability to degrade aromatic and PAHs, were hybridized with probes of NAH and TOL plasmids as well as with genomic DNA of bacteria known to degrade a wide variety of PAHs. Only 14 strains that mineralized naphthalene and phenanthrene showed homology to one of the probes. The remaining isolates mineralized and/or oxidized various PAHs and hybridized with neither pure plasmids nor genomic DNA (Foght Westlake, 1991). 

The aromatic degradative pathways receiving the most attention include those for toluene, benzoate, PCBs, and naphthalene. Five completely independent routes of toluene catabolism have been well characterized for aerobic bacteria (Figure 11.1). To date, all five pathways have been described in Pseudomonas and Burkholderia, despite the fact that at least two have been shown to be encoded by broad-host-range degradative plasmids. 

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