Diversity and Bioactivity of Endophytic Actinobacteria Associated with the Roots of Artemisia herba-alba Asso from Algeria

The isolation of endophytic actinobacteria from the roots of wild populations of Artemisia herba-alba Asso, a medicinal plant collected from the arid lands of Algeria, is reported for the first time. Forty-five actinobacterial isolates were identified by molecular analysis and in vitro evaluated for antimicrobial activity and plant growth-promoting (PGP) abilities (1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, nitrogen fixation, phosphate and potassium solubilization, ammonia, and siderophores production). The phylogenetic relationships based on 16S rRNA gene sequences show that the genus Nocardioides (n = 23) was dominant in the sampled localities. The remaining actinobacterial isolates were identified as Promicromonospora (n = 11), Streptomyces (n = 6), Micromonopora (n = 3), and Saccharothrix (n = 2). Only six (13.33%) strains (five Streptomyces and one Saccharothrix species) were antagonistic in vitro against at least one or more indicator microorganisms. The antimicrobial activity of actinobacterial strains targeted mainly Gram-positive bacteria. The results demonstrate that more than 73% of the isolated strains had ACC deaminase activity, could fix atmospheric nitrogen and were producers of ammonia and siderophores. However, only one (2.22%) strain named Saccharothrix sp. BT79 could solubilize phosphorus and potassium. Overall, many strains exhibited a broad spectrum of PGP abilities. Thus, A. herba-alba provides a source of endophytic actinobacteria that should be explored for their potential biological activities.