The genes encoding the delta subunits of dinitrogenases 2 and 3 are required for mo-independent diazotrophic growth by Azotobacter vinelandii.
vnfG and anfG encode the delta subunits of alternative nitrogenases 2 and 3 in Azotobacter vinelandii, respectively. As a first step towards elucidating the role of these subunits, diazotrophic growth and acetylene reduction studies were conducted on mutants containing alterations in the genes encoding these subunits. Mutants containing a stop codon (C36stop) or an in-frame deletion in anfG were unable to grow in N-free, Mo-deficient medium (Anf-). Mutants in which cysteine 36 of AnfG (a residue conserved between VnfG and AnfG) was changed to Ala or Ser were Anf+. Thus, this conserved cysteine is not essential for the function of AnfG in dinitrogenase 3. A mutant with a stop codon in vnfG (C17stop) grew after a lag of 25 h in N-free, Mo-deficient medium containing V2O5. However, a Nif- Anf- strain with this mutation was unable to grow under these conditions. This shows that the vnfG gene product is required for nitrogenase 2-dependent growth. Strains with mutations in vnfG and anfG reduced acetylene to different degrees. This indicates that the delta subunits are not required for acetylene reduction by nitrogenases 2 and 3.
Waugh
S I
SI
Department of Microbiology, North Carolina State University, Raleigh 27695-7615.
Paulsen
D M
DM
Mylona
P V
PV
Maynard
R H
RH
Premakumar
R
R
Bishop
P E
PE
D000114:Acetylene / Q000378:metabolism; D016948:Azotobacter vinelandii / Q000235:genetics / Q000254:growth & development*; D001426:Bacterial Proteins / Q000032:analysis; D001483:Base Sequence; D015180:Electrophoresis, Gel, Two-Dimensional; D005798:Genes, Bacterial / Q000235:genetics*; D007527:Isoenzymes / Q000235:genetics*; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009584:Nitrogen / Q000378:metabolism; D009591:Nitrogenase / Q000235:genetics*; D010084:Oxidation-Reduction; D011487:Protein Conformation; D014638:Vanadates / Q000378:metabolism
D001426:Bacterial Proteins; D007527:Isoenzymes; D014638:Vanadates; D008982:Molybdenum; D009591:Nitrogenase; D009584:Nitrogen; D000114:Acetylene