Isolation of phytohormone-degrading bacteria interacting with tea (Camellia sinensis (L.) O. Kuntze) plant and soil, and determination of their enzyme activities

In this study, the aim was to isolate bacteria capable of degrading three different phytohormones, 1-aminocyclopropane-1-carboxylate (ACC), indole-3-acetic acid (IAA), and salicylic acid (SA), which play critical roles in plant growth and defense processes, from rhizosphere, phyllosphere, endophytic (root, leaf, seed), and soil samples associated with the tea plant (Camellia sinensis (L.) O. Kuntze). More than 100 isolates collected from various locations across Rize province were initially subjected to biochemical tests to screen for ACC deaminase, IAA degradation, and SA degradation activities. Activity analyses revealed that some isolates were capable of degrading more than one phytohormone. In particular, certain IAA-degrading strains also exhibited ACC deaminase activity, indicating a multi-faceted plant–bacteria interaction potential. In contrast, the ability to degrade SA was restricted to the SA-positive group, suggesting that this trait may have a narrower ecological distribution. The specific activity values for ACC deaminase-positive isolates ranged from 0 to 2.58 μmol α-KB mg⁻¹ h⁻¹. Representative strains with high enzymatic activity were selected from the isolates, and species-level identification was performed via 16S rRNA gene sequence analysis. Phylogenetic analyses revealed that the majority of the isolates were affiliated with the phylum Proteobacteria, with Pseudomonas, Burkholderia, and Acinetobacter being the dominant genera. As a result, the study demonstrated the presence of high-activity isolates among microbial communities associated with the tea plant, which can be considered potential PGPb (plant growth-promoting bacteria) candidates for agricultural biotechnology. These strains are valuable genetic resources that could be utilized in future greenhouse and field trials for biofertilizer and biocontrol applications.