Wn cells at any other concentration of cadmium; b : P,0.05 vs methanol-grown cells at any other concentration of cadmium; c acetate-grown cells vs 25, 50 and 100 mM cadmium, using the Student’s t-test. doi:10.1371/journal.pone.0048779.tTable 1. Methane production and cadmium accumulation in 
M. acetivorans cultured on acetate or methanol.acetyl-CoA and measuring the release of CoA with DTNB at 412 nm. As several different enzymes may release CoA from acetyl-CoA, this activity was also specifically determined by measuring the CO-dependent reduction of methyl viologen as MNS reported elsewhere [12]. Briefly, in an anaerobic sealed bottle the Hepes-Mg buffer +0.5 mM methyl viologen was saturated with CO by bubbling the gas for 30 min (UKI-1 cost reaction mixture); then, 1.2 mL of reaction mixture was poured into a sealed glass cuvette previously purged with CO. The reaction was started by adding 50 mg of protein and followed at 603 nm. 1326631 As control of the CODH/AcCoAs activity, the cytosolic fraction was gently mixed with air for 10 min, with the remaining activity being lower than 53 (n = 2) of that determined with saturating CO or acetyl-CoA (representative trace is shown in figure S2). Also, 0.5 mM sodium cyanide inhibited the reduction of methyl viologen coupled to CO oxidation by 8568 (n = 3) as reported previously for the enzyme from M. thermophila [17]. Carbonic anhydrase (CA) activity was determined by incubating 2.5? mg of cytosolic protein with 100 mM Na-bicarbonate in a sealed 10 mL bottle with rubber stopper. To detect the CO2 formation, 5 mL of the head space was taken and injected at different times (0, 30, 60 and 120 s) in a gas chromatograph equipped with a Thermal Conductivity Detector. CO2 formed in assay reaction buffer without enzyme and with boiled enzyme was subtracted from the CO2 formed with enzyme (representative traces are shown in figures S3 and S4).of cadmium removed 240 h(acetate) or 96 h (methanol)Methanol38623 5569 9406326b 13876225 4.160.03 4.660.2 9.663.8 5.960.6acetate1664cCd removed and accumulated nmol/total cell protein862c10.8.364.Methane produced mmol/240 h (acetate) or 96 h (methanol)methanol4.0860.4.160.4.160.4.560.acetate4.560.4.360.methanol4.460.4.660.8.961.mg of total protein/culture5.261.acetate9.663.10.7.961.5.660.Estimated Free [Cd2+] pM5.860.21.2.Total [CdCl2] mM6.460.5.161.8.962.4.760.4.160.Acetatea20546929bmethanolBiogas Production and Metal Removal(DTNB) and spectrophotometrically (methylene blue), respectively (mean 6 SE, n = 4); the ionic strength = 0.77, pH = 7.0 and temperature = 36uC. The log values of the equilibrium constants (Keq) for the association of the complexes were 13.4 and 20.13 for Cys-cadmium and Cys-Cd-Cys, and 6.1 for sulfide-cadmium [20]. Cells cultured on methanol showed similar growth 1326631 either in the absence or presence of up to 100 mM total CdCl2 (Fig. 1A and inset). With acetate, growth was slightly faster in cultures with 100 mM cadmium during the exponential phase (Fig. 1B and inset). To undoubtedly establish that the turbidity increase induced by cadmium was indeed reporting cell growth in acetate cultures, the growth rate (GR) and the duplication time (DT) were determined by using the curve of methane production vs time and assuming that methane production is proportional to the number of living cells present in the culture. The duplication times were similar to those reported previously for M. acetivorans [11]. No significant differences in GR values (0.06460.003 versus 0.062560.Wn cells at any other concentration of cadmium; b : P,0.05 vs methanol-grown cells at any other concentration of cadmium; c acetate-grown cells vs 25, 50 and 100 mM cadmium, using the Student’s t-test. doi:10.1371/journal.pone.0048779.tTable 1. Methane production and cadmium accumulation in M. acetivorans cultured on acetate or methanol.acetyl-CoA and measuring the release of CoA with DTNB at 412 nm. As several different enzymes may release CoA from acetyl-CoA, this activity was also specifically determined by measuring the CO-dependent reduction of methyl viologen as reported elsewhere [12]. Briefly, in an anaerobic sealed bottle the Hepes-Mg buffer +0.5 mM methyl viologen was saturated with CO by bubbling the gas for 30 min (reaction mixture); then, 1.2 mL of reaction mixture was poured into a sealed glass cuvette previously purged with CO. The reaction was started by adding 50 mg of protein and followed at 603 nm. 1326631 As control of the CODH/AcCoAs activity, the cytosolic fraction was gently mixed with air for 10 min, with the remaining activity being lower than 53 (n = 2) of that determined with saturating CO or acetyl-CoA (representative trace is shown in figure S2). Also, 0.5 mM sodium cyanide inhibited the reduction of methyl viologen coupled to CO oxidation by 8568 (n = 3) as reported previously for the enzyme from M. thermophila [17]. Carbonic anhydrase (CA) activity was determined by incubating 2.5? mg of cytosolic protein with 100 mM Na-bicarbonate in a sealed 10 mL bottle with rubber stopper. To detect the CO2 formation, 5 mL of the head space was taken and injected at different times (0, 30, 60 and 120 s) in a gas chromatograph equipped with a Thermal Conductivity Detector. CO2 formed in assay reaction buffer without enzyme and with boiled enzyme was subtracted from the CO2 formed with enzyme (representative traces are shown in figures S3 and S4).of cadmium removed 240 h(acetate) or 96 h (methanol)Methanol38623 5569 9406326b 13876225 4.160.03 4.660.2 9.663.8 5.960.6acetate1664cCd removed and accumulated nmol/total cell protein862c10.8.364.Methane produced mmol/240 h (acetate) or 96 h (methanol)methanol4.0860.4.160.4.160.4.560.acetate4.560.4.360.methanol4.460.4.660.8.961.mg of total protein/culture5.261.acetate9.663.10.7.961.5.660.Estimated Free [Cd2+] pM5.860.21.2.Total [CdCl2] mM6.460.5.161.8.962.4.760.4.160.Acetatea20546929bmethanolBiogas Production and Metal Removal(DTNB) and spectrophotometrically (methylene blue), respectively (mean 6 SE, n = 4); the ionic strength = 0.77, pH = 7.0 and temperature = 36uC. The log values of the equilibrium constants (Keq) for the association of the complexes were 13.4 and 20.13 for Cys-cadmium and Cys-Cd-Cys, and 6.1 for sulfide-cadmium [20]. Cells cultured on methanol showed similar growth 1326631 either in the absence or presence of up to 100 mM total CdCl2 (Fig. 1A and inset). With acetate, growth was slightly faster in cultures with 100 mM cadmium during the 
exponential phase (Fig. 1B and inset). To undoubtedly establish that the turbidity increase induced by cadmium was indeed reporting cell growth in acetate cultures, the growth rate (GR) and the duplication time (DT) were determined by using the curve of methane production vs time and assuming that methane production is proportional to the number of living cells present in the culture. The duplication times were similar to those reported previously for M. acetivorans [11]. No significant differences in GR values (0.06460.003 versus 0.062560.
