Evaluating tomato peel-based growth media for Bacillus and Lactobacillus strains: a sustainable alternative to conventional broths

Tomato peel waste, a major by-product of the tomato processing industry, represents a promising resource for microbial cultivation in sustainable agriculture due to its richness in polysaccharides and secondary metabolites. In this study, tomato peels were assessed as a low-cost carbon source for the growth of three bacterial strains: CAAd and SP23, which belong to Bacillus amyloliquefaciens, and a Apilactobacillus kunkeei strain, species widely employed as biocontrol agents (BCAs). The strains were cultivated in media containing Tryptic Soy Broth (TSB) or de Man–Rogosa–Sharpe Broth (MRSB), except for media prepared with glucose, and tomato peel at concentrations of 5, 10, 20, and 30g/L, prepared in four forms: (1) fresh filtrate, (2) fresh unfiltered, (3) dried, and (4) dried supplemented with glucose. These were compared to standard media (TSB for Bacillus, MRSB for Apilactobacillus). Bacterial growth was monitored by optical density (OD600) at 24h and 48 h (T1, T2). The results showed that SP23 showed the best and dose-dependent growth in dried peel+TSB media, outperforming the control at 30g/L. CAAd grew moderately in all peel-based media, with performance similar to TSB, suggesting limited exploitation of peel nutrients. A. kunkeei strain exhibited high initial growth in fresh unfiltered peel+MRSB, but this declined at T2, likely due to nutrient depletion or inhibition. These findings demonstrate that tomato byproducts could serve as an effective, low-cost growth substrate for industrially relevant bacteria. Further optimization could enhance its scalability, opening the way for greener biotechnology solutions. This research was carried out within the project PRIN 2022 PNRR (M4 C2. Investment 1.1.) - D.D. n. 1409 of 14/09/2022-BICONTRARIUM.