Sequencing, RFLP analyses and experiments utilizing a lacZ transcriptional reporter fused to the promoter regions of nahR and nahG in Pseudomonas putida Cg1 confirmed that regulation of naphthalene degradation in both P. putida Cg1 and the type strain, P. putida NCIB 9816-4, is consistent with that of NAH7 from P. putida G7. Two nahR knockout strains (RK1 and Cg1-NAHR from P. putida NCIB 9816-4 and Cg1, respectively) showed a growth defect in the presence of naphthalene as sole carbon and energy source. We hypothesized that nahR influences ecological fitness of bacteria in naphthalene-contaminated soil and tested this hypothesis using both parent and nahR-knockout strains introduced to soil microcosms with and without added naphthalene. After 21 days, loss of cell viability was pronounced in the presence of added naphthalene crystals for nahR mutants of both test bacteria, relative to the wild types. Diminished viable counts were attributed to toxicity. Thus, our data indicated that NahR in P. putida Cg1 is virtually identical to its homologues in other pseudomonads and that nahR is required for resistance to naphthalene toxicity, hence the persistence of bacterial cells in soil with high concentrations of naphthalene.
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology