Mechanism for nitrogen isotope fractionation during ammonium assimilation by Escherichia coli K12.

ABSTRACT: Organisms that use ammonium as the sole nitrogen source discriminate between [(15)N] and [(14)N] ammonium. This selectivity leaves an isotopic signature in their biomass that depends on the external concentration of ammonium. To dissect how differences in discrimination arise molecularly, we examined a wild-type (WT) strain of Escherichia coli K12 and mutant strains with lesions affecting ammonium-assimilatory proteins. We used isotope ratio mass spectrometry (MS) to assess the nitrogen isotopic composition of cell material when the strains were grown in batch culture at either high or low external concentrations of NH3 (achieved by controlling total NH4Cl and pH of the medium). At high NH3 (≥ 0.89 µM), discrimination against the heavy isotope by the WT strain (-19.2‰) can be accounted for

SUBMITTER: Vo J 

PROVIDER: S-EPMC3666723 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature