A possible mechanism of action of plant growth-promoting rhizobacteria (PGPR) strain Bacillus pumilus WP8 via regulation of soil bacterial community structure

Abstract

According to the traditional view, establishment and maintenance of critical population densities in the rhizosphere was the premise of PGPR to exert growth-promoting effects. In light of the facts that soil bacterial community structures can be changed by some PGPR strains including Bacillus pumilus WP8, we hypothesize that regulation of soil bacterial community structure is one of the plant growth-promoting mechanisms of B. pumilus WP8, rather than depending on high-density cells in soil. In this study, denaturing gradient gel electrophoresis (PCR-DGGE) was performed to evaluate the relationship between changes in soil bacterial community structure and growth-promoting effect on the seedling growth of fava beans (Vicia faba L.) during three successive cultivations. We found that B. pumilus WP8 lacks capacity to reproduce in large enough numbers to survive in bulk soil more than 40 days, yet the bacterial community structures were gradually influenced by inoculation of WP8, especially on dominant populations. Despite WP8 being short-lived, it confers the ability of steadily promoting fava bean seedling growth on soil during the whole growing period for at least 90 days. Pseudomonas chlororaphis RA6, another tested PGPR strain, exists in large numbers for at least 60 days but less than 90 days, whilst giving rise to slight influence on bacterial community structure. In addition, along with the extinction of RA6 cells in bulk soils, the effect of growth promotion disappeared simultaneously. Furthermore, the increment of soil catalase activity from WP8 treatment implied the ability to stimulate soil microbial activity, which may be the reason why the dominant population changed and increased as time passed. Our study suggests that regulation of treated soil bacterial community structure may be another possible action mechanism.

Taxonomic Identity Resolution of Highly Phylogenetically Related Strains and Selection of Phylogenetic Markers by Using Genome-Scale Methods: The Bacillus pumilus Group Case

“…safensis strains, including the Type strain FO-36b(T) [ 41 ], were only found in Cluster III, we propose that the B . pumilus strains WP8 [ 5 ], B4134, B4107, CCMA-560 [ 42 ] and Fairview [ 43 ] should be renamed as B . safensis .…”

Traits-Based Integration of Multi-Species Inoculants Facilitates Shifts of Indigenous Soil Bacterial Community

“…The direct effects of microbial inoculants promote plant growth had been extensively described ( Colla et al, 2015 ; Wang et al, 2017 ). Nowadays, some works had been suggested that regulation of soil bacterial community structure is one of the plant growth-promoting mechanisms of microbial inoculants ( Kang et al, 2013 ; Rodriguez-Caballero et al, 2017 ). Our results did support this opinion.…”

Taxonomic and Functional Changes of Bacterial Communities in the Rhizosphere of Kimchi Cabbage After Seed Bacterization with Proteus vulgaris JBLS202

“… Kang et al (2013) suggested that Bacillus pumilus might not maintain a high density population in the rhizosphere, but that its presence might have a crucial long-term impact on the surrounding microbiome, which consequently affects plant growth. Since the quality and quantity of root exudate nutrients can differ with plant age, plant growth stage also impacts the composition and abundance of the rhizosphere microbial community ( Liu et al, 2015 ).…”

“…Because of complex roles of the microbial inoculants in the introduced rhizosphere, the effects of introduced PGPRs on the rhizosphere microbial communities are still controversial ( Kang et al, 2013 ). For example, Chowdhury et al (2013) reported that PGPRs cause minor changes in the microbial community and Kozdrój (2008) found that they cause significant shifts.…”