Enhancing the AI-2/LuxS quorum sensing system in Lactiplantibacillus plantarum: Effect on the elimination of biofilms grown on seafoods.

The biofilm clustered with putrefying microorganisms and seafood pathogens could cover the surface of aquatic products that pose a risk to cross-contaminating food products or even human health. Fighting biofilms triggers synchronous communication associated with microbial consortia to regulate their developmental processes, and the enhancement of the quorum sensing system in Lactiplantibacillus plantarum can serve as an updated starting point for antibiofilm-forming strategies. Our results showed that the exogenous 25 mM L-cysteine induced a significant strengthening in the AI-2/LuxS system of Lactiplantibacillus plantarum SS-128 along with a stronger bacteriostatic ability, resulting in an effective inhibition of biofilms formed by the simplified microbial consortia constructed by Vibrio parahaemolyticus and Shewanella putrefaciens grown on shrimp and squid surfaces. The accumulation of AI-2 allowed the suppression of the expression of biofilm-related genes in V. parahaemolyticus under the premise of L. plantarum SS-128 treatment, contributing to the inhibition effect. In addition, strengthening the AI-2/LuxS system is also conducive to eliminating preexisting biofilms by L. plantarum SS-128. This study suggests that the enhancement of the AI-2/LuxS system of lactic acid bacteria enables the regulation of interspecific communication within biofilms to be a viable tool to efficiently reduce and eradicate potentially harmful biofilms from aquatic product sources, opening new horizons for combating biofilms.

Phycocyanin ameliorates mouse colitis via phycocyanobilin-dependent antioxidant and anti-inflammatory protection of the intestinal epithelial barrier.

Phycocyanin is a typical microalgal active compound with antioxidant and anti-inflammatory efficacy, and the pigment moiety phycocyanobilin has been recently proposed as its active structural component. Here, to explore the structural basis for phycocyanin's intestinal protective action, we evaluated the therapeutic effects and mechanism of action of phycocyanin and phycocyanobilin in dextran sodium sulphate (DSS)-induced colitis mice and in Caco-2 and RAW 264.7 cells. Phycocyanobilin was obtained by solvothermal alcoholysis of phycocyanin and characterized by spectroscopy and mass spectrometry methods. Phycocyanin, phycocyanobilin and a positive drug mesalazine were intragastrically administered to C57BL/6 mice daily for 7 days during and after 4-day DSS exposure. Clinical signs and colon histopathology revealed that phycocyanin and phycocyanobilin had an equivalent anti-colitis efficacy that was even superior to mesalazine. Based on biochemical analysis of colonic tight junction proteins, mucus compositions and goblet cells, and colonic and peripheral proinflammatory cytokines, phycocyanin and phycocyanobilin displayed equivalent intestinal epithelial barrier-protecting and anti-inflammatory potential that was evidently superior to that of mesalazine. Flow cytometry analysis of phycocyanobilin fluorescence in Caco-2 cells unveiled a similar uptake efficacy of phycocyanin and phycocyanobilin by intestinal epithelial cells. According to lactic dehydrogenase release, 2',7'-dichlorodihydrofluorescein fluorescence and methylthiazolyldiphenyl-tetrazolium bromide assay in Caco-2 cells, phycocyanin and phycocyanobilin could equally and effectively protect the intestinal epithelial barrier from oxidant-induced disruption. Phycocyanin and phycocyanobilin also showed equivalent anti-inflammatory effects in tumor necrosis factor-α-stimulated Caco-2 cells and in lipopolysaccharides- and tumor necrosis factor-α-activated RAW264.7 cells. Overall, our results demonstrate the phycocyanobilin-dependent anti-colitis role of phycocyanin via antioxidant and anti-inflammatory mechanisms.

Dissecting of the AI-2/LuxS Mediated Growth Characteristics and Bacteriostatic Ability of Lactiplantibacillus plantarum SS-128 by Integration of Transcriptomics and Metabolomics.

Lactiplantibacillus plantarum could regulate certain physiological functions through the AI-2/LuxS-mediated quorum sensing (QS) system. To explore the regulation mechanism on the growth characteristics and bacteriostatic ability of L. plantarum SS-128, a luxS mutant was constructed by a two-step homologous recombination. Compared with ΔluxS/SS-128, the metabolites of SS-128 had stronger bacteriostatic ability. The combined analysis of transcriptomics and metabolomics data showed that SS-128 exhibited higher pyruvate metabolic efficiency and energy input, followed by higher LDH level and metabolite overflow compared to ΔluxS/SS-128, resulting in stronger bacteriostatic ability. The absence of luxS induces a regulatory pathway that burdens the cysteine cycle by quantitatively drawing off central metabolic intermediaries. To accommodate this mutations, ΔluxS/SS-128 exhibited lower metabolite overflow and abnormal proliferation. These results demonstrate that the growth characteristic and metabolism of L. plantarum SS-128 are mediated by the AI-2/LuxS QS system, which is a positive regulator involved in food safety. It would be helpful to investigate more bio-preservation control potential of L. plantarum, especially when applied in food industrial biotechnology.

Effect of purity of tea polysaccharides on its antioxidant and hypoglycemic activities.

The effects of purity of tea polysaccharides (TPS) on its five antioxidant activities and hypoglycemic activities in vitro were studied. The results showed that the higher the purity of TPS, the lower the antioxidant capacity. The purity of FTPSI is the highest (sugar content 80.72%), but its antioxidant activities were lower than those of Fujian tea polysaccharides (FTPS) and FTPSII. The antioxidant activity of tea polysaccharide is related to its protein and polyphenol content (Pearson r > .90). The protective effect of Zhejiang tea polysaccharides and FTPS on human umbilical vein endothelial cells (HUVEC) was better than that of its purified fractions. The inhibition rates of FTPSII (5 and 2 mg/ml) on α-glucosidase (32.76%) and α-amylase (-11.93%) were higher than those of FTPS and FTPSII. Purification does not change the basic structure of TPS. This study has certain reference value for the study of the antioxidant activities of TPS. Meanwhile, TPS can be used as a potential resource with hypoglycemic function. PRACTICAL APPLICATIONS: A large number of studies have shown that TPS have antioxidant activity. However, several studies considered that the antioxidant activity of TPS mainly comes from the residues of tea polyphenols. Therefore, the in vitro and cell antioxidant activities of TPS were studied in this paper. We believe that both glycoprotein and tea polyphenol are antioxidants of tea, and tea polysaccharide perform preferable effect on hypoglycemic. HUVEC cell model and four in vitro antioxidant test methods were used to study the antioxidant activities of TPS, and two enzyme inhibition activities were used to study the hypoglycemic effect of TPS, in order to provide a theoretical basis for the study of biological activity of TPS.

Effects of intrinsic metal ions of lentinan with different molecular weights from Lentinus edodes on the antioxidant capacity and activity against proliferation of cancer cells.

In this study, effects of intrinsic metal ions in lentinan on its bioactivities were evaluated. Lentinan extracted from Lentinus edodes was separated to four fractions with different molecular weights with Sephadex G-200 gel chromatography, and intrinsic metal ions were removed by EDTA. The ferrous ion chelating capacity of ELWs was measured to estimate EDTA residue after extensive dialysis. Antioxidant and antitumor activities of the isolated lentinans (LWs and ELWs) were investigated in vitro and compared, respectively. The results indicated that all of the isolated lentinan contained a large amount of intrinsic metal ions and the fraction with the lowest Mw had highest metal content. After removing intrinsic metal ions, the polysaccharides showed lower ABTS and DPPH radicals scavenging capacity and the reduced inhibition of the proliferation of BXPC-3 and Hela cells. Our results indicated that the metal ions in lentinan had positive effects on its bioactivities.