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J. Bacteriol., Mar 1995, 1505-1510, Vol 177, No. 6
SI Waugh, DM Paulsen, PV Mylona, RH Maynard, R Premakumar and PE Bishop
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.
Copyright © 1995, American Society for Microbiology
The genes encoding the delta subunits of dinitrogenases 2 and 3 are required for mo-independent diazotrophic growth by Azotobacter vinelandii
Department of Microbiology, North Carolina State University, Raleigh 27695-7615.
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