Application of rhizobacteria increases soil microbiome diversity, study reveals

Some bacteria that live in association with plant roots produce substances called exopolysaccharides, which are genes that encode the production of polysaccharides excreted by the bacteria and that help in the adhesion and protection of these bacteria. A study, conducted in collaboration between Embrapa Meio Ambiente and the University of Delaware, in the United States (USA), focused on a strain of Bacillus subtilis and highlighted the relevance of some bacterial genes not only for plant development, but also for the modulation of soil microbial communities. 

"In this pioneering study," explains Rodrigo Mendes, a researcher at Embrapa Meio Ambiente, "we showed that the genes responsible for the production of these exopolysaccharides are essential for bacteria to establish themselves in the roots and promote plant growth. Furthermore, we discovered that these genes, when present in an inoculant, can modify the community of other bacteria and fungi that live in the rhizosphere, influencing the entire soil microbiome around the roots."  

Caroline Nishisaka, a scholarship holder at Embrapa Meio Ambiente, explains that the results reveal that the presence of exopolysaccharide genes in the chosen strain is vital for the modulation of soil microbial communities. 

“In soils with lower microbial diversity, the absence of these genes, as observed in plants inoculated with the mutant strain, resulted in significant changes in the bacterial and fungal communities of the rhizosphere. This change demonstrates the essential role of these genes in social interactions and microbial community dynamics, which directly impacts plant health and growth,” highlights Nishisaka.

Furthermore, occurrence network analysis in the study indicated that the absence of exopolysaccharide genes affects the structure and dynamics of bacterial networks in the rhizosphere. Understanding these genetic characteristics is essential to understand how growth promoters interact with the rhizosphere microbiome and consequently influence plant growth. The application of this knowledge could revolutionize agricultural practices, especially in environments with reduced microbial diversity.

Bacillus subtilis is widely recognized for its ability to promote plant growth and mitigate abiotic and biotic stresses. Previous studies have shown that this bacterium is effective in promoting the growth of several crops, such as tomatoes, cucumbers, and wheat, as well as offering protection against soil-borne pathogens. More recently, evidence suggests that B. subtilis and other species of the genus can induce drought tolerance in plants, forming biofilms on the roots and helping to retain moisture.

Research also indicates that the application of rhizobacteria, such as B. subtilis, in agricultural settings can significantly alter the resident soil microbiome, increasing bacterial diversity in the rhizosphere. This highlights the importance of understanding the complex interactions between plants, soil microorganisms, and applied inoculants to optimize plant health and crop yield.

For Rodrigo Mendes, a researcher at Embrapa Meio Ambiente, this pioneering study reinforces the importance of these genetic characteristics for root colonization and the formation of the rhizosphere microbiome.

The findings highlight the need for further research into the interactions between plant growth promoters and the rhizosphere microbiome, especially in soils with low microbial diversity. Understanding these interactions may be key to developing new agricultural management strategies that utilize bacterial inoculants more effectively, promoting healthy plant growth and agricultural sustainability.

Optimizing these approaches could have a profound impact on agriculture, enabling more efficient use of rhizobacteria to improve plant health and increase agricultural productivity, especially in settings where soil microbial diversity is limited.

The study suggests that future research should further investigate the specific genetic characteristics of the microbiome and their implications for rhizosphere colonization, aiming to optimize approaches based on plant growth-promoting rhizobacteria.

The study suggests that future research should further investigate the specific genetic characteristics of the microbiome and their implications for rhizosphere colonization, aiming to optimize approaches based on plant growth-promoting rhizobacteria.

The study is by Caroline Sayuri Nishisaka, João Paulo Ventura, Rodrigo Mendes, Embrapa Meio Ambiente, Harsh Bais, Department of Plant and Soil Sciences, University of Delaware, USA.