This study evaluated the antagonistic activity of the cell-free supernatant of Lacticaseibacillus rhamnosus ATCC 9595 (Lcr-CFS) against Listeria monocytogenes, a major foodborne pathogen, that represents a challenge to food safety, due to its remarkable tolerance to environmental stresses and strong biofilm-forming ability. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Lcr-CFS against L. monocytogenes were defined as 31.25 and 62.5 mg/mL, respectively. Time-kill assays revealed dose- and time-dependent bactericidal effects. At sub-MICs, Lcr-CFS significantly reduced L. monocytogenes biofilm formation, disrupted preformed biofilms and decreased cell viability (80.3–96.7%), effects that were confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and fluorescence microscopy. Transmission electron microscopy showed L. monocytogenes cell wall damage, cytoplasmic leakage, and morphological alterations consistent with bactericidal effects. Additionally, exposure to 1x and 2x MIC of Lcr-CFS induced reactive oxygen species (ROS) accumulation, indicating oxidative stress as part of the mechanism by which Lcr-CFS exerts its antimicrobial activity. Gene expression analysis revealed upregulation of stress and virulence-associated genes (sigB, prfA, degU, flaA, motA, hlyA, pclA, and actA) upon exposure to 0.5x MIC suggesting a complex cross-talk network between adaptive mechanisms and environmental stresses. Although L. monocytogenes initiates a stress response, it appears unable to counteract the damage induced by Lcr-CFS, resulting in cell death. These findings highlight the antimicrobial and anti-biofilm properties of Lcr-CFS against L. monocytogenes. Given its in vitro efficacy, Lcr-CFS emerges as a promising biocontrol agent to improve food safety by mitigating the persistence of L. monocytogenes in food processing settings.

This work describes the bioprospection and characterization of cellulase-producing bacteria isolated from the soil obtained in a preserved region of the Cerrado biome, in Uberaba, Brazil. Cellulolytic activity was confirmed in 14 of the 84 bacterial strains isolated. According to enzymatic quantification, five strains were selected as the best cellulase producers, and based on the partial sequencing of the 16S rRNA gene the strains were identified as Bacillus siamensis (isolate AB-9;5.000U/mL), Bacillus toyonensis (isolate AB-1;4.630U/mL), Bacillus methylotrophicus (isolates MB-3;4.236U/mL and MP-7;4.282U/mL), and Bacillus drentensis (isolate ME-2;4.444U/mL). The enzymatic extract obtained from B. siamensis AB-9 was the most stable in different pH values (2-8), maintaining its cellulolytic activity, while B. toyonensis AB-1 and B. methylotrophicus MP-7 produced cellulases with maximum activity at pH 7 and 8. The cellulases produced by B. siamensis AB-9 and B. toyonensis AB-1 showed high enzymatic activity at all temperatures analyzed (10-80°C), while B. methylotrophicus MB-3 cellulases had maximum activity in the range of 20-70°C. To our knowledge, this is the first time that cellulase-producing bacteria isolated from Brazilian Cerrado biome in the region of Triângulo Mineiro with potential biotechnological application are described.

Nanotechnology offers innovative opportunities for developing functional materials with applications across biomedical and food-related fields. Among metallic and metal oxide nanostructures, niobium-based compounds have recently attracted attention due to their remarkable mechanical strength, corrosion resistance, thermal conductivity, and biocompatibility. In this study, niobium oxide nanostructures were synthesized through a green, cell-free approach using supernatants derived from lactic acid bacteria (LAB) Lacticaseibacillus rhamnosus and Lacticaseibacillus paracasei UFTM 2.9. The use of LAB supernatants provided an eco-friendly and sustainable route for nanoparticle production, avoiding toxic reagents while exploiting biologically active metabolites for bioreduction and stabilization. The synthesized nanostructures were characterized by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX), scanning-transmission electron microscopy (STEM), ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) and zeta potential analysis. In vitro assays using Vero-CCL81 cells demonstrated that the nanostructures exhibited low cytotoxicity, confirming their potential biocompatibility. Antibacterial and antibiofilm activities were evaluated against Escherichia coli ATCC 25922, revealing significant inhibitory effects. These findings highlight a novel and sustainable route for producing niobium oxide nanostructures via LAB-mediated synthesis, with promising implications for biomedical and food safety applications.

Green synthesis represents an environmentally benign and sustainable strategy for producing nanomaterials with enhanced biological functionality and reduced toxicity. Niobium has shown great potential as a biomaterial under physiological conditions. This study aimed to investigate the use of natural antioxidants, ascorbic acid (AA), tannic acid (TA), and quercetin (QUE), as eco-friendly reducing and stabilizing agents in the green synthesis of niobium-based nanomaterials (Nb_nano). The obtained nanomaterials were characterized by UV-Vis spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning-transmission electron microscopy (STEM), scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX), and zeta potential analysis, indicating the formation of hydrated niobium pentoxide (Nb₂O₅·nH₂O) nanomaterials with well-preserved structural organization and morphology. Acute cytotoxicity assays using VERO-CCL81 cells revealed that antioxidant-mediated synthesis significantly reduced the toxic effects of Nb_nano, increasing their cytocompatibility. All nanomaterials exhibited antibiofilm activity against Escherichia coli, effectively reducing bacterial adhesion and biofilm formation. Except for AA-mediated Nb_nano, the systems also demonstrated bactericidal activity, revealing their dual action against planktonic and sessile bacterial forms. Overall, the green synthesis of niobium nanomaterials using natural antioxidants represents a sustainable and effective strategy for developing multifunctional materials with promising antibacterial and antibiofilm performance, coupled with reduced cytotoxicity. These findings highlight the potential of niobium-based nanomaterials for biomedical and antifouling applications. Graphical Abstract