Vanadium and molybdenum requirement for the fixation of molecular nitrogen by two Methanosarcina strains

Abstract

Nitrogen fixation of the Methanosarcina barkeri strains “Fusaro” (DSM 804) and “227” (DSM 1538) was found to be dependent on the presence of vanadium or molybdenum whereby molybdenum (added as Na2-molybdate) was preferred to vanadium (added as VCl3). Strain “227” showed less pronounced effects on diazotrophic growth with respect to vanadium and molybdenum. Rhenium (ReCl3) or tungsten (Na2-tungstate) could not replace vanadium or molybdenum. The optimum concentrations were found to be 2μM for vanadium and 5μM for molybdenum (strain “Fusaro”). This Mo optimum of methanogenesis was 10-fold higher with N2 than with NH4Cl as nitrogen source. A vanadium requirement with NH4Cl could not be detected. No interferences were observed if molybdenum and vanadium were added simultaneously under diazotrophic conditions. Growth yields were smallest for strain “227” grown diazotrophically (\(Y_{CH_3 OH}\)=0.6g dw/mol in the presence of vanadium and \(Y_{CH_3 OH}\)=0.9g dw/mol in the presence of molybdenum), obviously higher for strain “Fusaro” grown diazotrophically (\(Y_{CH_3 OH}\)=1.15g dw/mol in the presence of V and \(Y_{CH_3 OH}\)=1.4g dw/mol with Mo) and highest if M. barkeri was grown on NH4Cl as N-source (\(Y_{CH_3 OH}\)=3.4g dw/mol with Mo, strain “Fusaro”).