Paenibacillus maysiensis sp. nov., a Nitrogen-Fixing Species Isolated from the Rhizosphere Soil of Maize.

A novel bacterium SX-49T with nitrogen-fixing capability was isolated from the rhizosphere soil of maize. Phylogenetic analysis of nifH gene fragment and 16S rRNA gene sequence revealed that the strain SX-49T is a member of the genus Paenibacillus. Values of 16S rRNA gene sequence similarity were highest between SX-49T and P. jamilae DSM 13815T (97.0%), P. brasiliensis DSM 14914T (97.8%), P. polymyxa DSM 36T (97.5%), and P. terrae DSM 15891T (98.8%). The similarity between SX-49T and other Paenibacillus species was < 97.0%. DNA-DNA hybridization values between strain SX-49T and the four type strains were P. jamilae DSM 13815T: 40.6%, P. brasiliensis DSM 14914T: 27.9%, P. polymyxa DSM 36T: 29.2%, and P. terrae DSM 15891T: 66.4%. The DNA G+C content of SX-49T was 46.4 mol%. The predominant fatty acids were anteiso-C15:0, C16:0 and iso-C16:0. The predominant isoprenoid quinone was MK-7. The genome contains 5628 putative protein-coding sequences (CDS), 6 rRNAs and 56 tRNAs. The phenotypic and genotypic characteristics, DNA-DNA relatedness, and genome features suggest that SX-49T represents a novel species of the genus Paenibacillus, and the name Paenibacillus maysiensis sp. nov. is proposed.

Comparative genomic analysis of N2-fixing and non-N2-fixing Paenibacillus spp.: organization, evolution and expression of the nitrogen fixation genes.

We provide here a comparative genome analysis of 31 strains within the genus Paenibacillus including 11 new genomic sequences of N2-fixing strains. The heterogeneity of the 31 genomes (15 N2-fixing and 16 non-N2-fixing Paenibacillus strains) was reflected in the large size of the shell genome, which makes up approximately 65.2% of the genes in pan genome. Large numbers of transposable elements might be related to the heterogeneity. We discovered that a minimal and compact nif cluster comprising nine genes nifB, nifH, nifD, nifK, nifE, nifN, nifX, hesA and nifV encoding Mo-nitrogenase is conserved in the 15 N2-fixing strains. The nif cluster is under control of a σ(70)-depedent promoter and possesses a GlnR/TnrA-binding site in the promoter. Suf system encoding [Fe-S] cluster is highly conserved in N2-fixing and non-N2-fixing strains. Furthermore, we demonstrate that the nif cluster enabled Escherichia coli JM109 to fix nitrogen. Phylogeny of the concatenated NifHDK sequences indicates that Paenibacillus and Frankia are sister groups. Phylogeny of the concatenated 275 single-copy core genes suggests that the ancestral Paenibacillus did not fix nitrogen. The N2-fixing Paenibacillus strains were generated by acquiring the nif cluster via horizontal gene transfer (HGT) from a source related to Frankia. During the history of evolution, the nif cluster was lost, producing some non-N2-fixing strains, and vnf encoding V-nitrogenase or anf encoding Fe-nitrogenase was acquired, causing further diversification of some strains. In addition, some N2-fixing strains have additional nif and nif-like genes which may result from gene duplications. The evolution of nitrogen fixation in Paenibacillus involves a mix of gain, loss, HGT and duplication of nif/anf/vnf genes. This study not only reveals the organization and distribution of nitrogen fixation genes in Paenibacillus, but also provides insight into the complex evolutionary history of nitrogen fixation.