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Production of antimicrobial activity by Bacillus sp. P11 was tested on different byproducts of food industry, like fish meal, grape waste, an industrial fibrous soybean residue, soybean meal, and cheese whey. Bacillus sp. P11 produced the higher amount of antimicrobial activity on soybean meal, followed by fish meal and fibrous soybean residue. Soybean meal was the selected medium to determine the effect of three variables (temperature, initial pH, and substrate concentration) on bacteriocin activity by response surface methodology, using a 2 3 factorial design. Statistical analysis showed good adequacy to the model (R 2 of 0.8268). In the range studied, temperature and initial pH of the medium have a significant effect on bacteriocin production, and substrate concentration has no significant effect. Response surface data showed maximum bacteriocin production at initial pH between 7.0 and 8.5 and temperature between 39 and 42°C. In the optimum conditions (initial pH 7.0 and 42°C), production of bacteriocin activity by Bacillus sp. P11 was compared using a commercial medium (BHI broth) and soybean meal. Maximum activity achieved with the soybean meal-based medium was similar to that obtained with BHI, indicating that soybean meal may be a cost-effective substrate for production of antimicrobial activity by Bacillus sp. P11.

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Temperature and pH are key factors influencing the production of antimicrobial peptides. In this work, qRT-PCR methodology was used to demonstrate the effect of these two variables on sboA (subtilosin A) and ituD (iturin A) expression in Bacillus sp. P11, an isolate from aquatic environment of the Amazon. Bacillus sp. P11 was incubated in BHI broth for 36 h at 30, 37 and 42 °C, and the pH values were 6.0, 7.4 and 8.0. The production of subtilosin A and iturin A was confirmed by mass spectrometry. The sboA expression increased 200-fold when the initial pH was 8.0. In contrast, ituD expression was maximum at pH 6.0. Increased temperature (42 °C) was adverse for both genes, but ituD expression increased at 37 °C. Expression of sboA and ituD was strongly affected by pH and temperature and qRT-PCR proved to be a powerful tool to investigate the potential of Bacillus strains to produce subtilosin A and iturin A.