Optimization of abamectin production by Streptomyces avermitilis and its antagonistic activity against Meloidogyne incognita.

This study aims to evaluate the safety of Streptomyces avermitilis and its extracts, as well as the impact of temperature, pH, and salinity on its growth, nematicidal activity, and abamectin production. It also determines the optimal conditions that promote significant mycelium and abamectin yield. S. avermitilis’ extract was found to be non-toxic to human skin fibroblasts and certain selected microorganisms. The highest mycelium dry weight and nematicidal effectiveness (99%) were achieved at pH 7 after 8 days of incubation at 28 °C, with a weight of 6.45 g/L at 0.1% NaCl and 7.81 g/L at 1% NaCl. The production medium supported significantly the highest mycelium production (23.57 g/L) and abamectin yield (3.23 g/L) as well as the highest specific growth rate (µ = 0.65/d), and multiplication rate (MR) (0.93) and the lowest doubling time td (1.06 d). Taguchi design screened seven variables, and identified potato starch, α-amylase, and incubation period as significant factors (p ≤ 0.05). The Box-Behnken design yielded maximum mycelium (71.08 g/L) and abamectin production (8.30 g/L) under optimal conditions of 150 g/L potato starch, 0.15 g/L α-amylase, and a 10-day incubation period. This investigation demonstrates the strong potential of S. avermitilis as an eco-friendly biocontrol agent against M. incognita and highlights the power of response surface methodology in optimizing secondary metabolite production for commercial and agricultural applications.