Identification of Streptomyces strains isolated from Humulus lupulus rhizosphere and determination of plant growth promotion potential of selected strains.

In the present study it was aimed to obtain novel strains of actinomycetes that have the ability to promote plant growth. For this, seven soil samples from the rhizosphere of Humulus lupulus (Pazaryeri, Bilecik) were used and potential isolates were obtained. 16S rRNA genes of 30 isolates were amplified by PCR and sequenced. Eighteen isolates were found to be closely related to Streptomycetes spp. and they were tested for their proteolytic activity, cellulase activity, phosphate solubility, IAA production, biofilm formation, and growth in nitrogen-limited medium. Two isolates, HCI 12 and HCI 36, were selected according to the results of these tests and their effects on growth of tomato plants (Solanum lycopersicum) were determined. Results indicated that the HCI 12 and HCI 36 strains caused a significant increase in root and shoot lengths, dry/fresh weights, and vigor index values compared to the control. The change in macromolecular structure including carbohydrates, proteins, and lipids of tomato plants with HCI 12 and HCI 36 inoculation was determined by Fourier transform infrared (FTIR) analysis. The results obtained from FTIR analysis were used in principal component analysis to evaluate changes in amide, carbohydrate, and lipid ratios of plant leaves due to microorganism application. Inoculation with the HCI 12 and HCI 36 strains caused a significant increase in the total carbohydrate and lipid ratio of tomato.