VALORIZATION OF TOMATO PLANT WASTES AND OPTIMIZATION OF GROWTH CONDITIONS FOR INDOLE-3-ACETIC ACID PRODUCTION BY Streptomyces plicatus STRAIN PT2

This study focused on the production of the phytohormone indole-3-acetic acid (IAA) using tomato plant tissues as feedstock and on highlighting its growth promotion effect on tomato seedlings. Twelve actinobacterial strains were screened for IAA production under standard growth conditions and the strain Streptomyces plicatus PT2 was selected as a promising producer. The establishment of growth conditions to increase IAA production by S. plicatus PT2 was conducted using Plackett-Burman mathematical design with seven variables. The variables L-tryptophan quantity and tomato roots-extract rate were the two significant variables influencing IAA production. The most impacting variables were optimized using the surface methodology (RSM) formulated according to the Central Composite Design (CCD). The optimized broth supplemented with 4 mg L-1 of L-tryptophan and 25% of tomato roots-extract significantly improved the IAA production from 96.3 µg mL-1 within 120h to a maximum of 110.29 µg mL-1 within 96h. The in-planta application of the produced IAA and a chemical IAA showed a significant increase in the dry weight, the shoot and root lengths of tomato seedlings. This is the first study showing the production of IAA using Streptomyces plicatus strain PT2 by exploring tomato plant tissues and its plant-growth promotion efficacy compared to a chemical marketed one. These results support a reasonable approach for the valorization of abundant worldwide tomato plant wastes in the phytohormones production bioprocesses.