Dual antibacterial mechanism of [K4K15]CZS-1 against Salmonella Typhimurium: a membrane active and intracellular-targeting antimicrobial peptide.

Salmonella genus is a leading cause of food-borne infections with strong public health impact and economic ramifications. The development of antimicrobial resistance added complexity to this scenario and turned the antibiotic drug discovery into a highly important challenge. The screening of peptides has served as a successful discovery platform to design new antibiotic candidates. Motivated by this, the antimicrobial and cytotoxic properties of three cruzioseptins against Salmonella Typhimurium and RAW 264.7 murine macrophage cells, respectively, were investigated. [K4K15]CZS-1 was the most potent antimicrobial peptide identified in the screening step with a minimum inhibitory concentration (MIC) of 16 µg/mL (7.26 µM) and moderate cytotoxicity. From a structural point of view, in vitro and in silico techniques evidenced that [K4K15]CZS-1 is a α-helical cationic antimicrobial peptide. In order to capture mechanistic details and fully decipher their antibacterial action, we adopted a multidimensional approach, including spectroscopy, electron microscopy and omics analysis. In general lines, [K4K15]CZS-1 caused membrane damage, intracellular alterations in Salmonella and modulated metabolic pathways, such as the tricarboxylic acid (TCA) cycle, fatty acid biosynthesis, and lipid metabolism. Overall, these findings provide deeper insights into the antibacterial properties and multidimensional mode of action of [K4K15]CZS-1 against Salmonella Typhimurium. In summary, this study represents a first step toward the screening of membrane-acting and intracellular-targeting peptides as potential bio-preservatives to prevent foodborne outbreaks caused by Salmonella.

Metabolomic and secretomic approach to the resistance features of the fungus Aspergillus niger IOC 4687 to copper stress.

Metabolomic and secretomic analyses of Aspergillus niger IOC 4687 indicated the features of resistance of this strain to copper stress. To investigate the metabolites produced under oxidative stress conditions, gas chromatography-mass spectrometry analysis was performed. The secretome principal component analysis results showed that mannitol could be the main metabolite responsible for conferring resistance to the fungus, and gluconic acid is the possible cause of copper desorption because of its chelating ability. The meta-analysis of the metabolome of A. niger IOC 4687 indicated that a low concentration of sorbitol and ribonolactone during growth may be an indicator of oxidative stress.

Response mechanism of mine-isolated fungus Aspergillus niger IOC 4687 to copper stress determined by proteomics.

Proteomic analysis of the fungus Aspergillus niger showed that its capacity to absorb metals was boosted by physiological modification under metal stress conditions. To investigate the proteome elicited by copper stress, the mine-isolated strain A. niger IOC 4687 was cultured in the absence (control) or presence of copper ions (50 mg L-1) for 72 h. Protein extract from each treatment was analyzed by nano-liquid chromatography-mass spectrometry and proteins were identified using PEAKS Studio 8.5 software. Grouping proteins by functional category showed that antioxidant enzymes, such as catalase, superoxide dismutase, and cytochrome c peroxidase, were present in both treatments. However, heat shock proteins (Hsp60 and Hsp70) and some metalloproteins (LMBR1 domain protein and A. niger contig An09c0040) were only observed after copper treatment. These proteins were the cellular response to the stress conditions. In conclusion, significant changes in the proteome of A. niger were observed due to the presence of copper.