Plant Stress (Jun 2024)
A root-associated Bacillus albus LRS2 and its metabolites for plant growth promotion and drought stress tolerance in little millet (Panicum sumatrense L.)
Abstract
The exploitation of drought-tolerant plant-associated bacteria in sustainable agriculture is considered potential for boosting plant growth and development under adverse environments featured by low water potentials. Herein, the present study aimed to decode the drought-tolerant root-associated bacteria from little millet (Panicum sumatrense L.). A sum of 25 bacterial isolates was obtained from roots of little millet (Var. ATL1) grown under induced drought conditions (-10 bars). They were initially assessed for their capacity to tolerate the drought up to – 36.6 bars (-3.6 MPa) on PEG (PEG 6000) infused agar plates and of which, 9 isolates (LRS1, LRS2, LRS6, LRS9, LRS14, LRS17, LRS22, LRS23, LRS25) were selected. Further, the cultures were assessed for their plant growth-promoting (PGP) traits such as the production of 1-aminocyclopropane-1-carboxylate deaminase (ACCd), exopolysaccharide (EPS), siderophore, indole acetic acid (IAA), ammonia, and hydrogen cyanide (HCN) and plant nutrition properties including phosphorous, potassium, and zinc. Of three isolates, LRS2 produced the highest ACCd (147 mol α- ketobutyrate mg protein–1h–1), IAA (15.89 μg mL–1), siderophore (54.85 % ) and P solubilization compared to other isolates. Further, the potential isolates LRS2, LRS22 and LRS23 were identified as Bacillus albus, Bacillus amyloliquefaciens and Enterobacter sp. respectively based on 16S rRNA sequence analysis. Biotization of little millet seeds (ATL1) with these strains showed that the inoculation of B. albus LRS2 elevated the plant germination (33 %), shoot length (13.5 %), and root length (25.2 %) followed by LRS23 with plant germination (22 %), shoot length (12.2 %) and root length (13.2 %) under induced drought stress (-0.45 MPa). Besides, metabolite profiling of B. albus LRS2 under induced stress analyzed in GC–MS yielded several drought-tolerant metabolites belonging to the class viz., organic acids, fatty acids, amino acid and its derivatives, organoheterocyclic compounds, and benzenoids. The compounds responsible for drought tolerance such as phenol, proline, fumaric acid, ascorbic acid, and gibberellic acid are more pronounced under induced drought stress (PEG 6000) which would aid in drought stress tolerance and facilitate plant health and fitness. These results implied that B. albus LRS2, a root-associated drought-tolerant endophytic bacteria, would enhance plant growth under drought stress, and lay a foundation for developing a novel bioinoculant for mitigating abiotic stress and promoting sustainable little millet production.
