Abstract

A COMPARATIVE STUDY ON NITROGEN FIXATION IN PULSES

Brij Mohan Singh, Chandra Mohan Rajoriya, Aashiq Hussain, Rajveer Singh Rawat and Dr. Bhanwar Lal Jat*

Abstract

In recent years, our understanding of biological nitrogen fixation has been bolstered by a diverse array of scientific techniques. Still, the origin and extant distribution of nitrogen fixation has been perplexing from a phylogenetic perspective, largely because of factors that confound molecular phylogeny such as sequence divergence, paralogy, and horizontal gene transfer. Here, we make use of 110 publicly available complete genome sequences to understand how the core components of nitrogenase, including NifH, NifD, NifK, NifE and NifN proteins, have evolved. These genes are universal in nitrogen fixing organisms- typically found within highly conserved operons-and overall, have remarkably congruent phylogenetic histories. Additional clues to the early origins of this system are available from two distinct clades of nitrogenaseparalogs; a grou composed of genes essential to photosynthetic pigment biosynthesis and a group of uncharacterized genes present in methanogens and in some photosynthetic bacteria. We explore the complex genetic history of the nitrogenase family, which is replete with gene duplication, recruitment, fusion and horizontal gene transfer and discuss these events in light of the hypothesized presence of nitrogenase in the last common ancestor of modern organisms, as well as the additional possibility that nitrogen fixation might have evolved later, perhaps in methanogenicarchaea and was subsequently transferred into the bacterial domain.

Keywords: NifH, NifD, NifK, NifE and NifN.