# Bacillus velezensis Ag129 and Ag132: two novel probiotics enhancing drought tolerance and agronomic performance in maize and soybean

## TL;DR

Two new probiotic bacteria, Bacillus velezensis Ag129 and Ag132, improve drought tolerance and crop yields in maize and soybean.

## Contribution

Identification and validation of two novel Bacillus velezensis strains with plant growth-promoting traits for drought resilience.

## Key findings

- Ag129 and Ag132 increased maize yields by 10.01% and 8.79%, respectively, under drought conditions.
- Both strains improved soybean yields by 10.82% and 15.20%, with consistent performance across environments.
- Genomic analysis revealed traits like IAA production, biofilm formation, and stress response relevant to drought resilience.

## Abstract

Water deficit is one of the main challenges to yield stability in tropical agricultural systems. This study aimed to identify bacterial strains capable of promoting plant growth and mitigating drought effects across different crop species. Initially, eight Bacillus strains were evaluated under water-deficit conditions in both growth chamber (Arabidopsis thaliana) and greenhouse experiments (common bean, soybean, and maize). Based on agronomic performance, two strains (Ag129 and Ag132) were selected for further validation under field conditions in different edaphoclimatic conditions. In maize, mean yield increases of 10.01% and 8.79% were observed for Ag129 and Ag132, respectively. In soybean, the average gains were 10.82% and 15.20% relative to the uninoculated control, with broad production stability across environments. Genome sequencing identified both strains as Bacillus velezensis (4,046,556 and 4,039,722 bp; GC 46.14% and 46.22%). We annotated 3,005 and 3,169 coding sequences, of which 2,861 and 3,011 were assigned to 22 COG categories. KEGG mapping allocated 2,259 and 2,369 genes to 252 and 265 pathways, respectively. Functionally, both genomes harbor a broad repertoire of plant growth-promoting traits relevant to drought resilience, including responses to abiotic stress, phytohormone biosynthetic potential (indole-3-acetic acid and cytokinins), phosphate solubilization, iron acquisition, and exopolysaccharide production/biofilm formation. These genomic features are consistent with our in vitro analyses, which confirmed high capacity for exopolysaccharide and biofilm production. Moreover, both strains produce indole-3-acetic acid (IAA), are compatible with Bradyrhizobium japonicum and Azospirillum brasilense, and exhibit antagonistic activity against soilborne phytopathogens, highlighting their biotechnological potential for inoculant development.