Characteristics and product analysis of naphthalene degradation by Pseudomonas stutzeri YC-YH1

Abstract:

[Objective] Naphthalene is the simplest of polycyclic aromatic hydrocarbons and is considered as an environmental pollutant that has gained a lot of public concern owing to its carcinogenicity and persistent organic properties. Biodegradation is generally recognized as the mass balance-wise most important route of naphthalene degradation. A previous study has revealed that Pseudomonas stutzeri YC-YH1 could degrade naphthalene effectively. This study aimed to characterize degradation, optimize the degradation rate of Pseudomonas stutzeri YC-YH1 for naphthalene and investigate naphthalene degradation pathways. [Methods] Firstly, effects of pH, temperature, inoculum amount and initial concentration of naphthalene for the naphthalene-degrading rate of Pseudomonas stutzeri YC-YH1 were determined by single factor experiments. Then based on the results of the single factor experiments, the software Design Expert 8.0.5 and Box-Behnken design was used to analyze and optimize the model of naphthalene degradation rate by three key factors (pH, temperature, and inoculums amount) through response surface methodology. LC-MS was used to analyze the degradation pathway and products. [Results] An optimization model was then constructed, and its validity was verified. The model was significant (P<0.001) and fitting well. In confirming experiments, under the optimization condition of temperature 32.4 °C, pH 7.10, inoculation 5.74% (V/V), the degradation rate of 100 mg/L naphthalene was 100% after incubation for 3 days. LC-MS data indicate that it is possible to find three major metabolites of naphthalene, which include 1,2- dihydroxynaphthalene, salicylic acid and catechol. [Conclusion] The results suggested that three key factors (pH, temperature, and inoculums amount) could affect the degradation rate of naphthalene, and optimization of the response surface methodology could improve the biodegradation efficiency of naphthalene by Pseudomonas stutzeri YC-YH1. The possible degradation pathway of strain YC-YH1 was catechol pathway. Naphthalene was first turned into1,2-dihydroxynaphthalene, and then salicylic acid and pyrocatechol, finally entered the tricarboxylic acid cycle.