1.1. Bacterial strain and culture conditions
The PAH-degrading bacteria, Sphingomonas sp. AJ1, was pur- chased from the Biological Resource Center of the National Insti- tute for Technology and Evaluation, Japan. Sphingomonas sp. AJ1
is a well-known PAH-degrader and this particular isolate has been reported to metabolize naphthalene and phenanthrene (Iwabuchi et al., 1994; Komukai-Nakamura et al., 1996). The cells were reju- venated in 3.74% Difco 2216 Marine broth and then transferred in 5.51% Difco 2216 marine agar plates. The agar growths were incu- bated at 25 °C (Sanyo Incubator). For a typical inoculum build-up, 10 mL of 3.74% Difco 2216 Marine broth was inoculated with cells from the agar plates and then incubated at 25 °C for 48 h under continuous shaking at 150 rpm (Taitec Bioshaker BR-300LF). The average final cell concentration of shake flask cultures was 2 £ 109 CFU mL¡1.