Evolution and Functional Analysis of Within Gene Cluster from RSA19.

is a genus of Gram-positive, facultative anaerobic and endospore-forming bacteria. Genomic sequence analysis has revealed that a compact (nitrogen fixation) gene cluster comprising 9⁻10 genes () is conserved in diazotrophic species. The evolution and function of the gene within the gene cluster of species is unknown. In this study, a careful comparison analysis of the compositions of the gene clusters from various diazotrophs revealed that located downstream of was identified in anaerobic , the facultative anaerobic species and aerobic diazotrophs (e.g., and ). The predicted amino acid sequences encoded by the gene, part of the gene cluster in RSA19, showed 60⁻90% identity with those of the genes located downstream of from different diazotrophic species, but shared no significant identity with those of the genes from different taxa of diazotrophic organisms. Transcriptional analysis showed that the gene was expressed under nitrogen fixation conditions from the promoter located upstream from . Mutational analysis suggested that the gene functions in nitrogen fixation in the presence of a high concentration of O₂.