Isolation of nitrogen-fixing bacteria containing molybdenum-independent nitrogenases from natural environments

Abstract

Seven diazotrophs that grow well under Mo-deficient, N(2)-fixing conditions were isolated from a variety of environments. These isolates fall in the gamma subdivision of the class Proteobacteria and have genes that encode the Mo nitrogenase (nitrogenase 1) and the V nitrogenase (nitrogenase 2). Four of the isolates also harbor genes that encode the iron-only nitrogenase (nitrogenase 3).

FIG. 1

Phylogenetic relationships between the environmental isolates and selected members of the Proteobacteria, as shown by an unrooted tree. Ten Pseudomonas strains used in the phylogenetic analysis are represented on the tree by Pseudomonas stutzeri. Bootstrap values (100 replicates) are shown at the branches for the environmental isolates; the values above the lines are DNA parsimony values, and the values below the lines are DNA maximum-likelihood values. Values less than 50% are not shown.

FIG. 2

Comparisons of the amino acid sequences of VnfG (A) and AnfG (B). The amino acid sequences were deduced from the DNA sequences of PCR products and were aligned by using the Clustal-W algorithm. The sequences of A. vinelandii VnfG and AnfG were obtained from references and , respectively.