Objective. To use municipal sewage sludge (LRM) from a wastewater treatment plant located in Toluca, State of Mexico, to grow the fungus Gibberella fujikuroi in submerged fermentation and to produce gibberellic acid (AG₃). Materials and methods. We used Gibberella fujikuroi (CDBB: 268). To obtain AG3, production was verified using as a substrate the standard culture medium (MCE). Gibberellic acid determination was done with high performance liquid chromatography (HPLC) with a Varian 9050.9012 equipment. We obtained 6 samples of sludge from a wastewater treatment plant in Toluca, State of Mexico, that were then characterized. Finally, both substrates (LRM and MCE) were used in submerged fermentation, and GA3 was obtained by extraction and quantified using HPLC. Results. The LRM characterization showed that the organic matter content (MO) is of 5.20% (w/v) and the total nitrogen content (N_T) is of 0.25% (w/v). Such composition is within the range as a substrate for the production of AG₃ by Gibberella fujikuroi. The fungus was cultivated for 3, 8, 13 and 30 days in sterile sewage sludge with a moisture content of 95.6% (w/v) and in standard culture medium (MCE). Samples were processed and analyzed by high performance liquid chromatography (HPLC). Production of AG₃ in the LRM was of 460.06 mg/L after 30 days in submerged fermentation at pH 4.0, and of 1,014.46 mg/L in the control. Conclusion. The nutrient content of LRM is suitable for the growth of the fungus Gibberella fujikuroi and for the production of GA₃ when used as a substrate.

Key words: gibberellic acid, Gibberella fujikuroi, sewage sludge