BackgroundCyanobacterial species have attracted research attention as potential sources of new biostimulants in the recent decade. In this study, the biostimulant activity of five cyanobacterial suspensions on the growth and essential oil composition of Thymus vulgaris L. was evaluated. Moreover, the expression of key genes involved in the biosynthesis of thymol and carvacrol, such as DXR and TPS2 genes were investigated.ResultsThe pot culture experiment revealed that cyanobacterial application significantly improved T. vulgaris L. growth indices, including plant height, dry and fresh weight, leaf and flower number, leaf area and photosynthetic pigments content. Total phenol and flavonoid contents in inoculated plants also showed a significant increase compared to the control. Anabaena torulosa ISB213 inoculation significantly increased root and shoot biomass by about 65.38% and 92.98% compared to the control, respectively. Nostoc calcicola ISB215 inoculation resulted in the highest amount of essential oil accumulation (18.08 ± 0.62) in T. vulgaris leaves, by about 72.19% compared to the control (10.5 ± 0.50%). Interestingly, the amount of limonene in the Nostoc ellipsosporum ISB217 treatment (1.67%) increased significantly compared to the control and other treatments. The highest expression rates of DXR and TPS2 genes were observed in the treatment of N. ellipsosporum ISB217, with 5.92‐fold and 5.22‐fold increases over the control, respectively.ConclusionThis study revealed the potential of the studied cyanobacteria as promising biostimulants to increase the production of biomass and secondary metabolites of T. vulgaris L., which could be a suitable alternative to chemical fertilizers from a biotechnological aspect.This article is protected by copyright. All rights reserved.