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Aim The aim of this study was to purify proanthocyanidins from areca nut seeds (P-AN) and to investigate the bactericidal activity and mechanism of the purified products against Streptococcus mutans. Methods and results Ultra-performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry, Fourier transform infrared, Matrix-assisted laser desorption/ ionization time of flight mass spectrometry (MADLI-TOF-MS), and thiolysis experiment were used for P-AN chemical analysis. Time-kill analysis and glycolytic pH drop were used to evaluate the activity of S. mutans in vitro. Meanwhile, the investigation of the bacteriostatic mechanism included membrane protein, fluidity, permeability, and integrity tests. The results showed that P-AN was a kind of proanthocyanidin mainly composed of B-type proanthocyanidins and their polymers. Moreover, MADLI-TOF-MS and thiolysis experiments demonstrated that the degree of polymerization of P-AN was 13. The time-kill analysis showed that P-AN had strong bactericidal activity against S. mutans. P-AN at minimum inhibitory concentration (MIC) concentrations was able to induce S. mutans death, while complete lethality occurred at 2 MIC. Glycolysis test showed that P-AN significantly inhibited S. mutans acid production (P  < .01). The morphological changes of S. mutans were observed by scanning electron microscopy and transmission electron microscopy experiments, which indicated that P-AN destroyed the cellular structure of S. mutans. At the same time, significant changes were observed in membrane proteins, fluidity, permeability, and integrity. Conclusion P-AN can effectively inhibit the activity of S. mutans. P-AN can reduce the erosion of the tooth surface by the acid of S. mutans. P-AN could break the structure of the cell membrane protein of S. mutans. P-AN could destroy the integrity of membrane, resulting in the death of S. mutans. [ABSTRACT FROM AUTHOR]

Different organic compounds can have varying degrees of impact on the activity of Lactobacillus paracasei. The study focused on the impact and action mechanism of different organic selenium products on the bioactivity of two strains of L. paracasei. The growth, antioxidant activity, extracellular polysaccharide secretion, quorum sensing (QS), and biofilm formation of the strains before and after the addition of organic selenium crude products and three organic selenium standard were evaluated. The results showed that the addition of crude organic selenium promoted the various activities of the strain. l‐selenocysteine had the strongest regulatory effect, with maximum GIM1.80 biofilm formation when it reached a critical concentration of 0.4 μg/mL; l‐selenomethionine resulted in the highest activity of the signal molecule Auto inducer‐2 of GDMCC1.155, when it reached a critical concentration of 0.4 μg/mL. The results of scanning electron microscopy demonstrated that the addition of organic selenium effectively improved the morphological structure of the two bacterial cells. Molecular docking revealed that the mechanism by which organic selenium regulates QS in Lactobacillus was achieved by binding two crucial receptor proteins (histidine protein kinase HKP and periplasmic binding protein LuxP) from specific sites. Furthermore, organic selenium products have a beneficial regulatory effect on the biological activity of L. paracasei. Overall, these findings provide a new alternative (organic selenium) for regulating the viability and beneficial activity of L. paracasei. Significance Statement: The study found that organic selenium can promote the growth, antioxidant activity, and biofilm formation of Lactobacillus by activating quorum sensing (QS). Uniquely, organic selenium can both positively and negatively regulate QS and biofilm formation of Lactobacillus, and critical concentrations have also been obtained. Furthermore, the regulating mechanism of organic selenium on the activity of Lactobacillus was revealed. This study provides a new alternative for regulating and stimulating the beneficial activity of probiotics. [ABSTRACT FROM AUTHOR]

Iturin, a metabolite produced by Bacillus subtilis, has a broad-spectrum antibacterial effect, and because they are secreted in the rhizosphere of plants, iturins are often mixed with many organic molecules. In recent years, people have improved their separation and purification methods but still cannot achieve simple and effective procedures, making Iturins an ideal biological control agent for insects and bacteria; commercial value still cannot be realized. With the in-depth studies of Iturins, its anti-cancer, hemolysis and other biological activities have gradually been discovered. This article reviews the branches of the Iturin family, structural features of these metabolite, separation and purification methods used for producing it, culture optimization, and various biological activities of the Iturin family, such as insecticidal, antibacterial, hemolytic and anticarcinogenic properties, among others have been summarized. Furthermore, this review revealed some commercial applications of Iturins and their relevance in research works. For example, in food packaging, clean water has good development potential.This can promote the commercial application of Iturins instead of other chemical and biological control agents that are environmentally friendly, pollution-free and have no side effects on humans. Furthermore, work documented anticancer, hemolytic and other biological activities of Iturin. [ABSTRACT FROM AUTHOR]