Chemical composition and antioxidant, antibacterial, allelopathic and insecticidal activities of essential oil of Thymus algeriensis Boiss. et Reut.

• The essential oil from T. algeriensis organs were analysed by GC and GC–MS.
• A significant variation of the oil composition attributed to organs was revealed.
• Oils exhibited remarkable inhibitory activity against five bacteria tested.
• The level of antioxidant activity of essential oils was moderate.
• The oils were found to possess strong allelopathic and insecticidal activities.

The present study describes chemical composition, antioxidant, antibacterial, allelopathic and insecticidal properties of essential oil of Thymus algeriensis (Lamiaceae), a North African endemic species. The essential oil from all organs of T. algeriensis were extracted by hydrodistillation and analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC–MS). A high variation among organs for the majority of compounds was shown. Caryophyllene oxide (21.1%) and veridiflorol (17.2%) were the main constituents in roots, while elemol (10.2%) and caryophyllene oxide (17.8%) were identified as the main constituents for stems. Leaves were characterized by high levels of α-pinene (19.5%), 1,8-cineole (11.6%) and camphor (10.4%). Based on the determination of the diameter of inhibition and the determination of the minimum inhibitory concentration, a moderate to high antibacterial activity according to oils was revealed against five bacteria strains. However, oils from Dj. Jdidi locality showed higher bactericidal effect (MICs = 1–3.25 μl/ml) than those from other samples. The level of antioxidant activity estimated by DPPH (IC50 = 4.31–9.23 mg/ml) and ABTS (11.69–28.23 μgTE/mg DW) test was moderate. The obtained results also showed that the leaf oils inhibited the shoot and root growth of Medicago sativa and Triticum æstivum seedlings. Thus, the T. algeriensis oils may be used as a natural herbicide. Furthermore, these oils were found to possess strong insecticidal activity (LC50 = 44.25–112.75 μl/l air) against cotton leafworm larvae. Thus, the essential oil of this plant could be used as a potential source of natural antioxidants and bioactive molecules in pharmaceutical as well as in food industries.