BackgroundMembers of the genus Paenibacillus are important plant growth-promoting rhizobacteria that can serve as bio-reactors. Paenibacillus polymyxa promotes the growth of a variety of economically important crops. Our lab recently completed the genome sequence of Paenibacillus polymyxa CR1. As of January 2014, four P. polymyxa genomes have been completely sequenced but no comparative genomic analyses have been reported.ResultsHere we report the comparative and genetic analyses of four sequenced P. polymyxa genomes, which revealed a significantly conserved core genome. Complex metabolic pathways and regulatory networks were highly conserved and allow P. polymyxa to rapidly respond to dynamic environmental cues. Genes responsible for phytohormone synthesis, phosphate solubilization, iron acquisition, transcriptional regulation, σ-factors, stress responses, transporters and biomass degradation were well conserved, indicating an intimate association with plant hosts and the rhizosphere niche. In addition, genes responsible for antimicrobial resistance and non-ribosomal peptide/polyketide synthesis are present in both the core and accessory genome of each strain. Comparative analyses also reveal variations in the accessory genome, including large plasmids present in strains M1 and SC2. Furthermore, a considerable number of strain-specific genes and genomic islands are irregularly distributed throughout each genome. Although a variety of plant-growth promoting traits are encoded by all strains, only P. polymyxa CR1 encodes the unique nitrogen fixation cluster found in other Paenibacillus sp.ConclusionsOur study revealed that genomic loci relevant to host interaction and ecological fitness are highly conserved within the P. polymyxa genomes analysed, despite variations in the accessory genome. This work suggets that plant-growth promotion by P. polymyxa is mediated largely through phytohormone production, increased nutrient availability and bio-control mechanisms. This study provides an in-depth understanding of the genome architecture of this species, thus facilitating future genetic engineering and applications in agriculture, industry and medicine. Furthermore, this study highlights the current gap in our understanding of complex plant biomass metabolism in Gram-positive bacteria.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-851) contains supplementary material, which is available to authorized users.

Background Paenibacillus polymyxa is a plant-growth promoting rhizobacterium that could be exploited as an environmentally friendlier alternative to chemical fertilizers and pesticides. Various strains have been isolated that can benefit agriculture through antimicrobial activity, nitrogen fixation, phosphate solubilization, plant hormone production, or lignocellulose degradation. However, no single strain has yet been identified in which all of these advantageous traits have been confirmed.Results P. polymyxa CR1 was isolated from degrading corn roots from southern Ontario, Canada. It was shown to possess in vitro antagonistic activities against the common plant pathogens Phytophthora sojae P6497 (oomycete), Rhizoctonia solani 1809 (basidiomycete fungus), Cylindrocarpon destructans 2062 (ascomycete fungus), Pseudomonas syringae DC3000 (bacterium), and Xanthomonas campestris 93-1 (bacterium), as well as Bacillus cereus (bacterium), an agent of food-borne illness. P. polymyxa CR1 enhanced growth of maize, potato, cucumber, Arabidopsis, and tomato plants; utilized atmospheric nitrogen and insoluble phosphorus; produced the phytohormone indole-3-acetic acid (IAA); and degraded and utilized the major components of lignocellulose (lignin, cellulose, and hemicellulose).Conclusions P. polymyxa CR1 has multiple beneficial traits that are relevant to sustainable agriculture and the bio-economy. This strain could be developed for field application in order to control pathogens, promote plant growth, and degrade crop residues after harvest.

Here we report the complete genome sequence of the bacterium Paenibacillus polymyxa CR1 (accession no. CP006941), which consists of one circular chromosome of 6,024,666 bp with 5,283 coding sequences (CDS), 87 tRNAs, and 12 rRNA operons. Data presented will allow for further insights into the mechanisms underpinning agriculturally and industrially relevant processes.