Click here to view fulltext PDF

Permanent link:
https://www.ias.ac.in/article/fulltext/jgen/069/02/0067-0078

Diazotrophs; nif genes; phylogeny; sequence analysis; dendrogram; evolution; nitrogenase

Hierarchical clustering and similarity coefficients of pairwise alignments of the published nucleotide sequences of 27nifH genes suggest thatnif genes are as ancient as the archaebacteria and clostridia. The positions ofnifHl ofMethanococcus thermolithotrophicus, nifH3 ofClostridium pasteurianum, nifH3 ofAzotobacter vinelandii andnifH ofFrankia suggest that a variety of lateral transfers may have occurred during evolution ofnifH gene. The genes for type 3 nitrogenase ofA. vinelandii may have diverged early from methanogens and clostridia. A high similarity coefficient with the derived amino acid sequence of type 3 nitrogenase suggests the presence of a functionally similar enzyme inC. pasteurianum. The type 2 nitrogenase genenifH2 of azotobacters seems to have originated recently from the genenifHl for conventional type I nitrogenase. RhizobialnifH genes comprise two closely related but discrete clusters that are in consonance with the plasmid or chromosomal location ofnif genes. The chromosomal and plasmid locatednifH of rhizobia seem to have evolved independently but contemporaneously.

Manjula Mathur¹ Rakesh Tuli¹

1. Molecular Biology and Agriculture Division, Bhabha Atomic Research Centre, Trombay, Bombay - 400 085, India

Published

August 1990

Manuscript received

27 January 1990