Bacillus subtilis strain IH7 was isolated from the rhi- zosphere of Tunisian healthy plants and selected for its antimicrobial activities against bacteria and fungi. This strain produced a novel antimicrobial peptide (bacteri-

Bacillus subtilis strain IH7 was isolated from the rhizosphere of Tunisian healthy plants and selected for its antimicrobial activities against bacteria and fungi. This strain produced a novel antimicrobial peptide (bacteriocin) called Bac IH7. The pure bacteriocin was obtained after precipitation by ammonium sulphate, chromatography on Sephadex G-25 and C18 reverse-phase HPLC. The SDS-PAGE analysis of purified Bac IH7 revealed a single band with an estimated molecular mass of approximately 14 kDa. Bac IH7 was sensitive to various proteases, thus proving to have protein nature and displayed a wide inhibitory spectrum towards Grampositive and Gram-negative bacteria and fungal pathogens. Purified Bac IH7 exhibited a bactericidal mode of action against Agrobacterium tumefaciens C58 and a fungistatic mode of action against Candida tropicalis R2 CIP203. Interestingly, based on conventional agronomic parameters for seed vigour, the application of Bac IH7 (800 AU) showed it to be a potent exogenous enhancer of growth that enhanced the vigour of tomato and muskmelon seedlings. Compared to the control, the germination percentage, shoot weight, shoot height, and root length were all significantly enhanced in the Bac IH7-treated plant seeds. Bac IH7 also exhibited effective disinfectant properties against seedborne diseases. In treated seeds, Bac IH7 had significant effects on the control of damping-off disease groups at the pre-germination stage, of root rot caused by Alternaria solani, as well as of wilt diseases and other bacterial seed-borne pathogens.