Pathogenic potential of bacteria isolated from commercial biostimulants

Daniela Bulgari,Silvia Filisetti,Matteo Montagna,Emanuela Gobbi,Franco Faoro

doi:10.1007/s00203-022-02769-1

Daniela Bulgari, Silvia Filisetti + Show 3 more

Open Access

https://doi.org/10.1007/s00203-022-02769-1

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Abstract

Microbial-based products are a promising alternative to agrochemicals in sustainable agriculture. However, little is known about their impact on human health even if some of them, i.e., Bacillus and Paenibacillus species, have been increasingly implicated in different human diseases. In this study, 18 bacteria were isolated from 2 commercial biostimulants, and they were genotypically and phenotypically characterized to highlight specific virulence properties. Some isolated bacteria were identified as belonging to the genus Bacillus by BLAST and RDP analyses, a genus in-depth studied for plant growth-promoting ability. Moreover, 16S rRNA phylogenetic analysis showed that seven isolates grouped with Bacillus species while two and four clustered, respectively, with Neobacillus and Peribacillus. Unusually, bacterial strains belonging to Franconibacter and Stenotrophomonas were isolated from biostimulants. Although Bacillus species are generally considered nonpathogenic, most of the species have shown to swim, swarm, and produced biofilms, that can be related to bacterial virulence. The evaluation of toxins encoding genes revealed that five isolates had the potential ability to produce the enterotoxin T. In conclusion, the pathogenic potential of microorganisms included in commercial products should be deeply verified, in our opinion. The approach proposed in this study could help in this crucial step.

Highlights

Microbial products represent a promising alternative to agrochemicals in a sustainable agriculture either as biopesticides or biofertilizers or biostimulants (Bulgari and Faoro 2018; Communicated by Erko Stackebrandt.Bulgari et al 2019; Pellegrini et al 2020)
Five colonies, identified by BLAST and RDP analyses on partial 16S rRNA gene sequences, resulted as belonging to the class of Gammaproteobacteria and assigned to the genus Franconibacter and Stenotrophomonas; 13 colonies belong to the phylum of Firmicutes and showed high identity values with members of the genus Bacillus, Neobacillus and Peribacillus (Table 2)
Bacillus were the most abundant microorganisms resulting present in the commercial biostimulants, Bacillus is a heterogeneous group of bacteria with a different impact on human life ranking from severe illness, food poisoning, industrial and agriculture applications

Summary

Introduction

Microbial products represent a promising alternative to agrochemicals in a sustainable agriculture either as biopesticides or biofertilizers or biostimulants (Bulgari and Faoro 2018; Communicated by Erko Stackebrandt.Bulgari et al 2019; Pellegrini et al 2020). Microbial products represent a promising alternative to agrochemicals in a sustainable agriculture either as biopesticides or biofertilizers or biostimulants Biostimulants are composed mainly by protein hydrolysates and other N-containing compounds, seaweed extracts, chitosan, humic, and fulvic acids, plant growth-promoting bacteria, and fungi (Yakhin et al 2017). Microorganisms can enhance plant growth directly by phosphate solubilization, atmospheric nitrogen fixation, iron chelation, and production of secondary metabolites or indirectly by protecting plant from pathogens deleterious effects (Hardoim et al 2015). Few genera are formulating for plant growth promotion or pest and pathogens control. Bacillus is a species-rich genus of Gram-positive rod-shape bacteria inhabiting different environments such as soil, water, and plants. Several strains of the species Bacillus amyloliquefaciens, B. subtilis, B. pasteurii, B. cereus, B. pumilus, B. mycoides, and B. sphaericus

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