First Report of Drought-Tolerant Halobacteria Associated with Agave potatorum Zucc

The rhizosphere microbiota of arid plants plays a crucial role in adaptation to environmental stress. However, few studies have characterized microorganisms associated with Agave species and their contribution to resilience against salinity and drought. This study aimed to isolate and characterize halotolerant bacteria from the rhizosphere of Agave potatorum Zucc from two different sites and evaluate their in vitro Na+ sequestration, desiccation resistance, and phytohormone production. These traits were compared with those of halotolerant bacteria isolated from a highly saline soil at a third site. Bacteria were obtained through serial dilutions and cultured on R2A plates supplemented with varying NaCl concentrations. The most efficient Na+-sequestering isolates underwent an 18-day desiccation assay, and their production of indole-3-acetic acid (IAA) and gibberellic acid (GA3) was quantified. Among the 48 halotolerant isolates obtained, 7 (SM1, SM10, SPM5, SM7, SM19, VZ9, and SPM1) exhibited the highest Na+ sequestration efficiency. Among these isolates, SM1 exhibited the highest in vitro Na+ sequestration capacity (10.74 μg L−1, p < 0.05). SM1 and SPM1 demonstrated the greatest desiccation resistance, at 88.39% and 83.05%, respectively. Additionally, SM7 produced the highest levels of IAA (13.69 μg mL−1, p < 0.05), while SM1 exhibited the highest GA3 production (1285.38 μg mL−1, p < 0.05). Based on these characteristics, isolates SPM1 and SM1 exhibited the highest efficiency in tolerating drought and salinity stress. However, isolate SPM1 may colonize the rhizosphere of A. potatorum more effectively, likely due to its adaptation as a native isolate to the edaphic and environmental conditions in which this agave thrives. Molecular identification confirmed that the isolates belong to the genera Kosakonia, Priestia, Streptomyces, Bacillus, Stutzerimonas, Pseudomonas, and Exiguobacterium. This study highlights the diversity of halotolerant bacteria in the rhizosphere of A. potatorum and their potential as bioinoculants for enhancing soil fertility and restoring degraded soils.