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N 2 ‐dependent growth and nitrogenase activity in the metal‐metabolizing bacteria, Geobacter and Magnetospirillum species

2000; Wiley; Volume: 2; Issue: 3 Linguagem: Inglês

10.1046/j.1462-2920.2000.00096.x

1462-2920

Dennis A. Bazylinski, Ann Dean, Dirk Schüler, Elizabeth J. P. Phillips, Derek R. Lovley,

Microbial Fuel Cells and Bioremediation

Cells of Geobacter metallireducens , Magnetospirillum strain AMB‐1, Magnetospirillum magnetotacticum and Magnetospirillum gryphiswaldense showed N 2 ‐dependent growth, the first anaerobically with Fe(III) as the electron acceptor, and the latter three species microaerobically in semi‐solid oxygen gradient cultures. Cells of the Magnetospirillum species grown with N 2 under microaerobic conditions were magnetotactic and therefore produced magnetosomes. Cells of Geobacter metallireducens reduced acetylene to ethylene (11.5 ± 5.9 nmol C 2 H 4 produced min −1 mg −1 cell protein) while growing with Fe(III) as the electron acceptor in anaerobic growth medium lacking a fixed nitrogen source. Cells of the Magnetospirillum species, grown in a semi‐solid oxygen gradient medium, also reduced acetylene at comparable rates. Uncut chromosomal and fragments from endonuclease‐digested chromosomal DNA from these species, as well as Geobacter sulphurreducens organisms, hybridized with a nifHDK probe from Rhodospirillum rubrum , indicating the presence of these nitrogenase structural genes in these organisms. The evidence presented here shows that members of the metal‐metabolizing genera, Geobacter and Magnetospirillum , fix atmospheric dinitrogen.