Bioprospecting of Rhizobacteria Producing ACC‐Deaminase That Contribute to Abiotic Stress Tolerance in Wheat

ABSTRACT

The present study focuses on the bioprospection of plant growth‐promoting rhizobacteria (PGPR), with particular emphasis on ACC deaminase (ACCD) production. In a preliminary screening, rhizospheric soil from seven weed plants from the semidesert of Coahuila was collected, and 55 ACCD+ bacteria were isolated in DF (Dworkin and Foster) medium supplemented with 1‐aminocyclopropane‐1‐carboxylic acid (ACC) as the unique source of nitrogen. The isolates exhibited multiple plant growth‐promoting (PGP) traits, including nitrogen fixation, high phosphate solubilization index, and high indole‐3‐acetic acid levels. Additionally, α‐ketobutyrate quantification was used to assess ACC deaminase activity across all isolates; M4B4, M2B4, and M1B7 exhibited high activity, at 0.94, 3.27, and 3.62 µmol KB mg ⁻¹ h ⁻¹ , respectively. Consequently, these three isolates were evaluated for saline and drought stress assays under in vitro conditions, with M2B4 showing slight growth at 1% NaCl; meanwhile, M2B4 and M4B4 showed greater increases with 5% polyethylene glycol. Bioassays on Arabidopsis thaliana Col‐0 inoculated with M4B4 significantly increased foliar area under in vitro conditions. The growth‐promoting effect was evaluated in wheat ( Triticum aestivum L.); M4B4 significantly increased root dry biomass compared with control plants. In wheat plants under abiotic stress, M2B4 exhibited greater size and stem diameter than the control at 175 mM NaCl, and M4B4 showed increased stem diameter at 200 mM. Furthermore, drought‐stressed wheat plants with M4B4 showed reduced stomatal conductance and transpiration. The isolates M2B4 and M4B4 were categorized as ACCD+ rhizobacteria and identified as Serratia and Citrobacter , respectively. Overall, these isolates have high potential as bioinoculants.