In this work, biosurfactant production by Bacillus subtilis #573 was evaluated using corn steep liquor (CSL) as culture medium. The best results were obtained in a culture medium consisting of 10% (v/v) of CSL, with a biosurfactant production of about 1.3 g/l. To the best of our knowledge, this is the first report describing biosurfactant production by B. subtilis using CSL as culture medium. Subsequently, the effect of different metals (iron, manganese and magnesium) on biosurfactant production was evaluated using the medium CSL 10%. It was found that for all the metals tested, the biosurfactant production was increased (up to 4.1, 4.4 and 3.5 g/l for iron, manganese and magnesium, respectively). When the culture medium was supplemented with the optimum concentration of the three metals simultaneously, the biosurfactant production was increased up to 4.8 g/l. Furthermore, the biosurfactant exhibited a good performance in oil recovery assays when compared with chemical surfactants, which suggests its possible application in microbial enhanced oil recovery or bioremediation

In this work, the antifungal activity of rhamnolipids produced by Pseudomonas aeruginosa #112 was evaluated against Aspergillus niger MUM 92.13 and Aspergillus carbonarius MUM 05.18. It was demonstrated that the di-rhamnolipid congeners were responsible for the antifungal activity exhibited by the crude rhamnolipid mixture, whereas mono-rhamnolipids showed a weak inhibitory activity. Furthermore, in the presence of NaCl (from 375 mM to 875 mM), the antifungal activity of the crude rhamnolipid mixture and the purified di-rhamnolipids was considerably increased. Dynamic Light Scattering studies showed that the size of the structures formed by the rhamnolipids increased as the NaCl concentration increased, being this effect more pronounced in the case of di-rhamnolipids. These results were confirmed by Confocal Scanning Laser Microscopy, which revealed the formation of giant vesicle-like structures (in the µm range) by self-assembling of the crude rhamnolipid mixture in the presence of 875 mM NaCl. In the case of the purified mono- and di-rhamnolipids, spherical structures (also in the µm range) were observed at the same conditions. The results herein obtained demonstrated a direct relationship between the rhamnolipids antifungal activity and their aggregation behaviour, opening the possibility to improve their biological activities for application in different fields.

Modern fruit crop production increasingly seeks sustainable strategies to enhance growth, yield, and fruit quality while minimizing environmental impacts. Plant biostimulants—naturally derived substances or beneficial microorganisms, such as seaweed and plant extracts, Plant-Growth-Promoting Rhizobacteria (PGPR), humic substances, protein hydrolysates, and Si—emerge as promising tools to achieve these goals by stimulating key physiological and biochemical processes. They can improve nutrient uptake and efficiency, modulate hormonal and metabolic pathways, and enhance the activity of enzymatic and non-enzymatic antioxidants, leading to improved plant vitality and fruit quality. Biostimulants also influence rhizosphere microbial communities and soil health, promoting nutrient cycling, beneficial microbial diversity, and soil structure. This review evaluates the application of biostimulants in fruit crops and their effects on growth, physiology, productivity, fruit quality, both chemical and nutritional composition and physical parameters. Challenges related to variability in efficacy, formulation standardization, and crop-specific responses are discussed, alongside future perspectives on integrating biostimulants into sustainable orchard management. Overall, biostimulants represent multifunctional tools that support both productivity and ecological sustainability in modern fruit production systems.