Culturable rhizosphere bacteria associated with Alcea nudiflora (Lindl.) Boiss. in the Zailiyskiy Alatau (Kazakhstan): isolation, characterization and functional potential

Abstract

Abstract The rhizosphere of medicinal plants represents a reservoir of culturable bacteria with potential value for plant protection and biotechnology. In this study, we characterized the culturable rhizosphere bacterial community associated with Alcea nudiflora (Lindl.) Boiss. collected from three sites in the Zailiyskiy Alatau. Rhizosphere microorganisms were isolated using tenfold serial dilutions followed by plating on meat-peptone agar and oatmeal agar, purified by streaking, and phenotypically characterized by colony morphology, Gram staining, and motility assays. Nineteen morphologically distinct isolates were recovered and grouped into four morphotypes: Streptomyces-like actinomycetes, Bacillus-like spore-forming rods, coryneform bacteria, and coccoid forms. All isolates showed a Gram-positive reaction. Antagonistic activity was screened using agar well diffusion, disk diffusion, and agar block assays against test microorganisms (Escherichia coli, Staphylococcus aureus, Candida albicans, C. utilis, Aspergillus niger, Fusarium oxysporum and Penicillium chrysogenum). Several isolates exhibited broad or target-specific antagonism, including strains 5/1 (balanced antibacterial and antifungal activity), 4/7 and 7/1 (anti-staphylococcal activity), 9/3 and 8/2 (antifungal activity, including against Candida spp.), and 1/2 (specific activity against A. niger). Overall, these results provide a baseline characterization of the culturable rhizosphere bacteria associated with Alcea nudiflora (Lindl.) Boiss. in this region and identify candidate isolates for molecular identification and plant-focused validation.