Evaluation of Mentha viridis and Opuntia ficus-indica juices as plant-based media for beneficial rhizosphere microbes

Synthetic culture media are often costly due to their chemical constituents, prompting interest in developing affordable plant-based alternatives. This study evaluated the potential of Mentha viridis (M. viridis) and Opuntia ficus-indica (O. ficus-indica) juices as culture media for supporting microbial growth, due to their high content of amino acids, vitamins, and minerals. A total of seven bacterial and eight actinomycete isolates were obtained from the rhizosphere of M. viridis, while ten bacterial isolates were recovered from O. ficus-indica. Screening for plant growth-promoting traits revealed that isolate B5 (Bacillus safensis FO-36b) produced the highest levels of indole acetic acid (10.3 mg/mL) and gibberellic acid (28.25 mg/mL), and together with actinomycete isolate A3 (Streptomyces afghaniensis NR-114833.1), showed the strongest phosphate solubilization capacity (877.07 and 758.43 µg/mL, respectively). Additionally, 60% of isolates grown on Mentha-based medium and 40% on Opuntia-based medium produced high levels of ammonia. These findings highlight the potential of plant-based media as cost-effective platforms for isolating and screening beneficial microbes with biofertilizer properties.