The excessive and irrational use of chemical fertilizers poses a series of environmental problems. A growing number of research studies have focused on the application of beneficial microorganisms to reduce the use of chemical fertilizers. Here, potato field experiments were conducted to investigate whether partial replacement of chemical fertilizers with bio-organic fertilizers containing Bacillus velezensis BA-26 had an effect on plant growth, soil fertility, and soil microbial community composition. Three treatment methods were used in this study: organic fertilizer (OF), bio-organic fertilizer (BOF), and chemical fertilizer (CF). The results showed that the biomass and soluble sugar content of potato were significantly increased with BOF treatment. The soil electrical conductivity, available phosphorus (AP), available potassium (AK), urease, and alkaline phosphatase activity also improved with BOF treatment. Further analysis revealed that BOF treatment increases bacterial diversity and reduces fungal diversity. Potentially, pathogenic microbials; such as Fusarium, Verticillium, and Botryotrichum; treated with BOF were significantly decreased compared with CF treatment. Redundancy analysis showed that soil conductivity and AP had significant effects on bacterial and fungal community composition. Thus, the results suggest that the application of bio-organic fertilizer could reduce the use of chemical fertilizers by promoting potato growth, improving soil fertility, and affecting microbial community composition.

Paenibacillus polymyxa is a well-known Gram-positive biocontrol bacterium. It has been reported that many P. polymyxa strains can inhibit bacteria, fungi and other plant pathogens. Paenibacillus polymyxa employs a variety of mechanisms to promote plant growth, so it is necessary to understand the biocontrol ability of bacteria at the genome level. In the present study, thanks to the widespread availability of Paenibacillus genome data and the development of bioinformatics tools, we were able to analyze and mine the genomes of 43 P. polymyxa strains. The strain NCTC4744 was determined not to be P. polymyxa according to digital DNA-DNA hybridization and average nucleotide identity. By analysis of the pangenome and the core genome, we found that the pan-genome of P. polymyxa was open and that there were 3,192 core genes. In a gene cluster analysis of secondary metabolites, 797 secondary metabolite gene clusters were found, of which 343 are not similar to known clusters and are expected to reveal a large number of new secondary metabolites. We also analyzed the plant growth-promoting genes that were mined and found, surpisingly, that these genes are highly conserved. The results of the present study not only reveal a large number of unknown potential secondary metabolite gene clusters in P. polymyxa, but also suggest that plant growth promotion characteristics are evolutionary adaptations of P. polymyxa to plant-related habitats.

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