[Characteristics and pathway of naphthalene degradation by Pseudomonas sp. N7].

The biodegradation characteristics of a typical polycyclic aromatic hydrocarbon, naphthalene by the strain (Pseudomonas sp. N7) were investigated by using HPLC and UV analytical techniques. The results showed that the addition of nutritious salt and microelements accelerated the degradation of naphthalene by 23.65%. Degradation efficiency increased with increasing dissolved oxygen and reached 95.66%, then remained stabilized when dissolved oxygen was over 4.3 mg/L, yet decreased with increasing naphthalene concentration. Neutral and weak alkaline condition favored the biodegradation with degradation capacity all over 82.88%. Pseudomonas sp. N7 had a maximum degradation capability of 95.66% when dealing with 100 mg/L naphthalene at 30 degrees C and pH 7.5 with 165 r/min rotary shaking for 72 h. By measuring the absorbance, pH and degradation of substrates during treatment of different substrate with strain N7, it was demonstrated that Pseudomonas sp. N7 could also degrade other aromatic hydrocarbons, such as toluene, dimethylbenzene, phenol, 2,4-nitrophenols, benzyl acid, 1-naphthol and salicylic acid, utilizing each of them as sole carbon and energy source for growth and breeding, thus showing its good biodegradation diversity. The pathway of naphthalene degradation was explored through analyzing metabolic intermediates at different degradation stages by using UV-Vis and GC-MS. The result revealed that there were two possible degradation pathways for naphthalene: one was phthalic acid pathway, and the other was that naphthalene was first oxidized to 1,2-dihydroxynaphthalene, and then the cleavage of rings caused the formation of salicylic acid, catechol, and 2-hydroxymuconic semial-dehyde. Finally these metabolites entered the tricarboxylic acid cycle (TCA).