After appropriate time intervals, 20 mL of the culture medium was withdrawn and the pH was adjusted to 2 with 6 M HCl and extracted three times with equal amount of ethyl acetate. The ethyl acetate phase was further extracted three times with an equal volume of NaOH (60 mL, 10 mM). The organic phase (neutral fraction) was dried over anhydrous Na2SO4 and the solvent was removed in vacuo. The residue was dissolved in 20 mL methanol and used for quantitative UV analysis at 267 nm. see more Chrysene utilization and

accumulation of metabolites were also demonstrated by changes in the UV-visible spectra of supernatants and by examination of metabolites accumulated in the spent medium by TLC and HPLC. Strain PNK-04 was grown in 100 mL PMS medium containing 100 mg 1-hydroxy-2-naphthoic acid

at 37 °C with shaking at 180 r.p.m. for 72 h. Cells were harvested by centrifugation (5000 g for 10 min) and the cell pellet was washed three times with phosphate Wnt antagonist buffer (50 mM, pH 7.0). Cells were then transferred to PMS medium containing 1 g L−1 chrysene. The washed cell suspension was incubated on a rotary shaker for 48 h (180 r.p.m., 37 °C). After centrifugation, the supernatant was adjusted to pH 2 with 6 M HCl and extracted twice with an equal volume of ethyl acetate. The organic phase was dried over anhydrous sodium sulphate and concentrated under vacuo. The residue was dissolved in 1 mL methanol and used for analysis. The metabolites were analysed by TLC on silica gel 60 plates

using the solvent system benzene/chloroform/methanol (6 : 4 : 1, v/v/v). Metabolites were initially tentatively identified by comparing their Rf values with those of authentic standards. Chrysene metabolites and the respective reference compounds were then analysed by HPLC (Shimadzu Corp., Japan) using an LC 10ATVP pump and a 250 × 4.6 mm C18 Inertsil ODS-8 column (particle size, 5 μm; Phenomenex) at a flow rate of 1 mL min−1. Injection of samples was via a Rheodyne injector equipped with a 20-mL sample loop. UV absorption was measured at 254 nm. The compounds were eluted using a linear gradient of 40–100% methanol/water gradient at 1 mL min−1 over 55 min. LC-ESI-MS of chrysene metabolites and respective authentic standards were recorded Mannose-binding protein-associated serine protease on a Micromass Quattro II triple quadrupole mass spectrometer (Waters, UK) connected to a JASCO PU-980 HPLC pump. The column was a PARTISIL-10 ODS-3 (250 × 4.6 mm, 5 μm, wavelength 254 nm). The solvent system was methanol/water gradient, at 0.8 mL min−1. Cell-free extracts were prepared by growing cells on chrysene, 1-hydroxy-2-naphthoic acid or salicylic acid according to the method of Veeranagouda et al. (2006). All the enzyme assays were performed using the crude enzyme. The reaction mixture of 1,2-dihydroxynaphthalene dioxygenase assay (Kuhm et al., 1991) contained 1 mL acetic acid–NaOH buffer (50 μmol, pH 5.5) and enzyme (0.1 mL). The reaction was initiated by the addition of 1,2-dihydroxynaphthalene (0.4 μmol) in tetrahydrofuran (10 μL).