First Report of Drought-Tolerant Halobacteria Associated with <i>Agave potatorum</i> Zucc

The rhizosphere microbiota of arid plants plays a crucial role in adaptation to environmental stress. However, few studies have characterized microorganisms associated with <i>Agave</i> species and their contribution to resilience against salinity and drought. This study aimed to isolate and characterize halotolerant bacteria from the rhizosphere of <i>Agave potatorum</i> 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, <i>p</i> < 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, <i>p</i> < 0.05), while SM1 exhibited the highest GA₃ production (1285.38 μg mL⁻¹, <i>p</i> < 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 <i>A. potatorum</i> 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 <i>Kosakonia</i>, <i>Priestia</i>, <i>Streptomyces</i>, <i>Bacillus</i>, <i>Stutzerimonas</i>, <i>Pseudomonas</i>, and <i>Exiguobacterium</i>. This study highlights the diversity of halotolerant bacteria in the rhizosphere of <i>A. potatorum</i> and their potential as bioinoculants for enhancing soil fertility and restoring degraded soils.