Abstract: The enrichment culture method was used to screen low temperature strains using naphthalene as the sole carbon source and energy source from the contaminated soil in Daqing Oilfield,Heilongjiang Province. The gas chromatography-mass spectrometry（GC-MS）was employed to study the degradation of naphthalene by degrading bacteria in naphthalene-inorganic salt medium. The single-factor test and orthogonal test were applied to determine and optimize the culture conditions of the degrading bacteria,and the main controlling factors in the degradation stage were analyzed. The results showed that 2 strains efficiently degrading naphthalene under low temperature condition were screened and named as GN1 and GN2. GN1 and GN2 rapidly degraded naphthalene under low temperature conditions. On the basis of the non-biological factors of the control group,the degradation rate of naphthalene（300 mg/L）reached 94.43% and 95.47% in 4 days,indicating that they had obvious advantages in tolerance and degradation rate. The 2 strains were identified as Pseudomonas by morphological observation,physiological and biochemical characteristics and 16S rDNA gene. The strains GN1 and GN2 grew best in naphthalene-inorganic salt medium（Naphthalene concentration 300 mg/L）,culture temperature 15℃,initial pH 6.0,culture rotation 180 r/min,and culture time 7 d. The growth of the 2 bacteria was significantly related to 5 environmental factors.

Key words: low temperature, naphthalene, biodegradation, Pseudomonas