STATISTICAL, MOLECULAR, AND ULTRASTRUCTURAL INSIGHTS INTO THE STRESS-ALLEVIATING POTENTIAL OF AUTOCHTHONOUS STEPPE BACTERIAL LINEAGES

Abstract

The identification and characterization of multi-stress tolerant Plant Growth-Promoting Bacteria (PGPB) are essential for developing sustainable agricultural strategies to mitigate the effects of abiotic stress factors and intensive agrochemical usage. This study aimed to evaluate the stress tolerance of eleven autochthonous strains isolated from steppe zone previously exposed to glyphosate application. Taxonomic identity was confirmed by 16S rRNA gene sequencing, resulting in a phylogenetically diverse collection of isolates belonging to the genera Pseudomonas spp., Paenibacillus spp., and Paenarthrobacter spp. The strains were subjected to a comparative tolerance screening under abiotic and xenobiotic stress, including osmotic, saline, and glyphosate exposure. Quantitative growth histograms revealed distribution of strains depending on stress factors, while principal component analysis (PCA) identified distinct clustering patterns, indicating genus-specific tolerance thresholds. Molecular screening detected the groL and ectA genes in Paenibacillus isolates, indicating potential roles in protein folding and osmoadaptation. Furthermore, ultrastructural scanning and transmission microscopic imaging revealed exopolysaccharide (EPS) production, suggesting its role in cellular protection. Overall, the eleven indigenous strains showed synergistic physiological, genetic, and structural adaptations, highlighting their potential as multi-functional bio-inoculants for stress-resilient agriculture.