Plant growth promoting potential of Bacillus, Azotobacter and Streptomyces bacteria from nettle rhizospheric soil

Abstract

The significance of employing Plant Growth Promoting (PGP) microorganisms holds immense value in the cultivation of medicinal plants, where the attainment of high-quality plant biomass is indispensable. Therefore, it becomes imperative to isolate and identify a diverse array of microorganisms from the rhizosphere of various plants and assess their efficacy in enhancing the growth of medicinal plants. The primary aim of this research was to isolate and characterize bacteria belonging to the Bacillus, Streptomyces, and Azotobacter genera from the rhizosphere of nettle (Urtica dioica L.). Additionally, the study explored the influence of the bacterial isolates on the germination of oregano (Origanum vulgare L.) and marjoram (Origanum majorana L.) seeds. Isolation, physiological characterization (the growth of isolates at different temperatures, levels of acidity and concentrations of NaCl, and resistance of isolates to Cd and Pb), biochemical characterization (the production of lipase, amylase, pectinase, and cellulase), and PGP characterization of isolates were performed. The impact of isolates on seed germination was monitored under controlled conditions. The count of sprouted seeds was assessed at 7- and 10-day intervals. The results of this study reveal that the isolated rhizospheric bacteria of nettle have multiple physiological, biochemical and PGP properties. All isolates showed good PGP potential, but the isolates Azotobacter A1 and Streptomyces Ac1 stood out. The applied isolates had a positive effect on the seed germination of oregano and marjoram, the best effect being exhibited by Bacillus B2 and Azotobacter A1 on the seed germination of oregano and by Bacillus B1 and Streptomyces Ac1 on that of marjoram.