Phytomicrobiome of Helianthus annuus: in vitro assessment of plant growth-promoting traits and heavy metal tolerance

Endophytic bacteria are usually found within plant tissues. They enhance plant growth, with potential agricultural and environmental applications. They might enhance the plant tolerance to abiotic stresses and inhibit the metal toxicity within metal hyperaccumulator plants. The majority of endophytic bacteria possess plant growth-promoting features. They secrete secondary metabolites that improve plant growth and physiological functions. Twelve endophytic bacteria strains were isolated from the root, stem and leaves of Helianthus annuus plant grown in contaminated soil with the heavy metals lead, zinc and chromium. The isolates were identified and characterized by colony morphology, biochemical tests including gram, spore staining, catalase, starch hydrolysis, hydrogen cyanide and auxin production, phosphate solubilization and nitrogen fixation, along with 16S rRNA gene-based molecular identification of bacteria. Five bacterial isolates showed positive results in all Plant growth-promoting traits. The molecular identification through amplification of bacteria's 16S rRNA using PCR has shown eight Bacillus spp., with two Acinetobacter spp., Providencia vermicola and Enterobacter cloacae. The findings highlight the diversity of endophytic bacteria associated with the COH3 variety of Helianthus annuus plant grown in HM-contaminated soil and evaluate their plant growth-promoting and heavy metal tolerance under in vitro conditions. Further studies are required to evaluate their efficiency under field conditions.