The Isolation And Characterization Of Salt-tolerant Naphthalene-degrading Bacteria

Backgroud information Polycyclic aromatic hydrocarbons (PAHs) are persistent toxic organic pollutants with long-term residual, high bioaccumulation, semi-volatility, carcinogenicity, mutagenicity and teratogenicity. PAHs can be widely distributed in environment due to their abilities to spread via organisms, air, water, soil etc., furthermore, PAHs are difficult to be degraded naturally, that is why now the treatment of PAHs is great contention at present. Comparing with chemical method and physical method, biodegradation is quite promising for removing PAHs pollution with convenience, low cost and no second pollutants.Objective The purpose of this study was to isolate several bacterial strains with high ability to degrade naphthalene, based on researches of bacterial identification, substrate profiles, naphthalene-degrading ability and detection of naphthalene-degrading genes and salt-tolerant genes.Methods1) Isolating naphthalene-degrading bacterium using MM medium plus naphthalene as sole carbon source by means of enrichment cultivation and dish sublimation; Analyzing the strains’basic features, e.g. salt-tolerant abilities, antibiotic resistance, substrate profiles, etc.2) Identifying the bacterial strains based on morphological analyses, biochemical tests, and16S rDNA sequence analyses.3) Detecting both naphthalene-degrading genes and salt-tolerant genes by PCR method to amplifiy related naphthalene dioxygenase gene fragments and salt-tolerant gene fragments using both chromosome DNA and plasmid DNA.4) Analyzing and comparing the naphthalene-degrading abilities of strains by HPLC method.Results1) Three salt-tolerant and naphthalene-degrading bacteria were isolated and named as RL1, RL2and RL3.2) All of three strains belong to Pseudomonas genus.3)10kb-size indigenous plasmid was isolated from each of three strains.4) There was no positive result for PCR amplification of both naphthalene dioxygenase genes and salt-tolerant genes.5) All of eight strains were able to degrade naphthalene, of which Pseudomonas sp. wjq3was the best in naphthalene degradation.Conclusions Three isolated bacteria were identified as Pseudomonas species, all of which can be salt-tolerant and be able to degrade naphthalene to some extent. There might be novel degradation pathways and salt-tolerant mechanism for these three strains. This research may be helpful to provide engineering bacteria for future bioremediation in saline-alkali and oil-polluted soil.