As described elsewhere [13]. Briefly, 1 mL of fresh medium was taken with a syringe from the anaerobic culture bottles and immediately filtered through a 0.45 mm (pore diameter) filter unit (Millex-HV, Millipore, Ireland) and injected (50 mL) into the HPLC apparatus. The concentration of thiol-groups was calculated by using the DTNB molar extinction coefficient of 13.6 mM21 cm21. Sulfide was also determined spectrophotometrically by the methylene blue formation as described by King and Morris [14] with some modifications: in 10 mL anaerobic bottles sealed with a butyl KS 176 rubber stopper and secured with an aluminum crimp collar, 23.7 mM zinc acetate, 60 mM NaOH, 0.18 mM 
N,N-dimethyl-p-phenylenediamine (DMPD) dissolved in 5 N HCl and 0.1 mL of culture medium, or different amounts of sulfide, were added by using a syringe and mixed until homogeneity. Then, 2.8 mM FeCl3 was added and incubated at room temperature for 30 min for color development (methylene blue formation). Final volume was 2.5 mL. Samples were measured at 670 nm under anoxic conditions in an anaerobic chamber. The sulfide contentabsorbance relationship was linear up to 350 nmol. Methane production and methanol were determined by gas chromatography (Shimadzu GC2010 apparatus), equipped with a capillary column HP-PLOT/U of 30 m length, 0.32 mm I.D. and 10 mm film (Agilent, USA) and flame ionization detector. MethaneBiogas Production and Metal Removal2.6 Cadmium removal and accumulationCells were harvested and washed as indicated above with 200 volumes of a solution containing 50 mM Tris-HCl, 2 mM MgCl2 and 2 mM EGTA (TME buffer) at pH 7.5; the pellet was resuspended in fresh buffer to give 5?0 mg protein/mL and frozen at 270uC until use. Aliquots of the cell suspension were digested with H2SO4+HNO3 (1:3) for 2 h at 100uC and the intracellular cadmium content determined by atomic absorption spectrophotometry (Varian Spectra AA 640).2.7 Ultrastructure analysisMethanol-grown cells with or without 100 mM CdCl2 were fixed by immersion in glutaraldehyde (3 , v/v, in phosphate buffer, pH 7.4), after removal from the culture medium, and dehydrated in graded ethanol. Samples of 1 mm2 containing the cells were cut out in cross section with a diamond knife and embedded in 1:1 epoxy resin. To determine cadmium and sulfur localization inside the cells, atomic-resolution high angle annular dark-field scanning-transmission electron microscopy (HAADFSTEM) was used as reported previously [18]. The protein content was determined after cells were washed once with TME buffer by the Biuret method with bovine serum albumin as standard as described previously [13]. For the statistical analysis of the data, the Student’s t-test or a two way ANOVA and Bonferroni post analyses were performed using the Graph Pad PRISM version 5.01 software.Results and Discussion Cadmium solubility and effect on cell growthBecause cysteine and sulfide present in the culture medium bind the cadmium added with high affinity, the (-)-Indolactam V biological activity soluble free Cd2+ concentrations were estimated (see Table I) by using the program Chelator [19] and the following physico-chemical conditions. The concentration of the reduced cysteine and sulfide in the medium determined experimentally were for cysteine 1.760.03 mM and for sulfide 1.2160.4 and 0.9560.03 mM as determined by HPLCData shown were obtained from cell cultures at the end of the growth curve. Values are the mean 6 SD of at least 4 cultures from different batches. a : P,0.05 vs acetate-gro.As described elsewhere [13]. Briefly, 1 mL of fresh medium was taken with a syringe from 
the anaerobic culture bottles and immediately filtered through a 0.45 mm (pore diameter) filter unit (Millex-HV, Millipore, Ireland) and injected (50 mL) into the HPLC apparatus. The concentration of thiol-groups was calculated by using the DTNB molar extinction coefficient of 13.6 mM21 cm21. Sulfide was also determined spectrophotometrically by the methylene blue formation as described by King and Morris [14] with some modifications: in 10 mL anaerobic bottles sealed with a butyl rubber stopper and secured with an aluminum crimp collar, 23.7 mM zinc acetate, 60 mM NaOH, 0.18 mM N,N-dimethyl-p-phenylenediamine (DMPD) dissolved in 5 N HCl and 0.1 mL of culture medium, or different amounts of sulfide, were added by using a syringe and mixed until homogeneity. Then, 2.8 mM FeCl3 was added and incubated at room temperature for 30 min for color development (methylene blue formation). Final volume was 2.5 mL. Samples were measured at 670 nm under anoxic conditions in an anaerobic chamber. The sulfide contentabsorbance relationship was linear up to 350 nmol. Methane production and methanol were determined by gas chromatography (Shimadzu GC2010 apparatus), equipped with a capillary column HP-PLOT/U of 30 m length, 0.32 mm I.D. and 10 mm film (Agilent, USA) and flame ionization detector. MethaneBiogas Production and Metal Removal2.6 Cadmium removal and accumulationCells were harvested and washed as indicated above with 200 volumes of a solution containing 50 mM Tris-HCl, 2 mM MgCl2 and 2 mM EGTA (TME buffer) at pH 7.5; the pellet was resuspended in fresh buffer to give 5?0 mg protein/mL and frozen at 270uC until use. Aliquots of the cell suspension were digested with H2SO4+HNO3 (1:3) for 2 h at 100uC and the intracellular cadmium content determined by atomic absorption spectrophotometry (Varian Spectra AA 640).2.7 Ultrastructure analysisMethanol-grown cells with or without 100 mM CdCl2 were fixed by immersion in glutaraldehyde (3 , v/v, in phosphate buffer, pH 7.4), after removal from the culture medium, and dehydrated in graded ethanol. Samples of 1 mm2 containing the cells were cut out in cross section with a diamond knife and embedded in 1:1 epoxy resin. To determine cadmium and sulfur localization inside the cells, atomic-resolution high angle annular dark-field scanning-transmission electron microscopy (HAADFSTEM) was used as reported previously [18]. The protein content was determined after cells were washed once with TME buffer by the Biuret method with bovine serum albumin as standard as described previously [13]. For the statistical analysis of the data, the Student’s t-test or a two way ANOVA and Bonferroni post analyses were performed using the Graph Pad PRISM version 5.01 software.Results and Discussion Cadmium solubility and effect on cell growthBecause cysteine and sulfide present in the culture medium bind the cadmium added with high affinity, the soluble free Cd2+ concentrations were estimated (see Table I) by using the program Chelator [19] and the following physico-chemical conditions. The concentration of the reduced cysteine and sulfide in the medium determined experimentally were for cysteine 1.760.03 mM and for sulfide 1.2160.4 and 0.9560.03 mM as determined by HPLCData shown were obtained from cell cultures at the end of the growth curve. Values are the mean 6 SD of at least 4 cultures from different batches. a : P,0.05 vs acetate-gro.