An Investigation of Quorum Sensing Inhibitors against Bacillus cereus in The Endophytic Fungus Pithomyces sacchari of the Laurencia sp.

Bacillus cereus, a common food-borne pathogen, forms biofilms and generates virulence factors through a quorum sensing (QS) mechanism. In this study, six compounds (dankasterone A, demethylincisterol A3, zinnimidine, cyclo-(L-Val-L-Pro), cyclo-(L-Ile-L-Pro), and cyclo-(L-Leu-L-Pro)) were isolated from the endophytic fungus Pithomyces sacchari of the Laurencia sp. in the South China Sea. Among them, demethylincisterol A3, a sterol derivative, exhibited strong QS inhibitory activity against B. cereus. The QS inhibitory activity of demethylincisterol A3 was evaluated through experiments. The minimum inhibitory concentration (MIC) of demethylincisterol A3 against B. cereus was 6.25 µg/mL. At sub-MIC concentrations, it significantly decreased biofilm formation, hindered mobility, and diminished the production of protease and hemolysin activity. Moreover, RT-qPCR results demonstrated that demethylincisterol A3 markedly inhibited the expression of QS-related genes (plcR and papR) in B. cereus. The exposure to demethylincisterol A3 resulted in the downregulation of genes (comER, tasA, rpoN, sinR, codY, nheA, hblD, and cytK) associated with biofilm formation, mobility, and virulence factors. Hence, demethylincisterol A3 is a potentially effective compound in the pipeline of innovative antimicrobial therapies.

Efficient extraction of flavonoids from Flos Sophorae Immaturus by tailored and sustainable deep eutectic solvent as green extraction media.

In the face of the many shortcomings of conventional organic solvents in the age of green chemistry, deep eutectic solvents (DESs) appear under the spotlight of natural product extraction because of its outstanding advantages. In this study, the extraction of six compounds from Flos Sophorae Immaturus (FSI) with DES-5 (choline chloride/1,4-butanediol) as its topgallant solvent was determined by screening nine DESs. After single factor test and BBD experiment, the optimum conditions of deep eutectic solvent-based microwave-assisted extraction (DES-MAE) were: choline chloride/1,4-butanediol (molar ratio of 1:2) and water content (25%, v/v), time 20 min, microwave power 600 W, temperature 62 ℃, liquid/solid ratio 26 mL/g. The extraction yields of rutin, nicotiflorin, narcissin, quercetin, kaempferol and isorhamnetin were 116.78, 15.01, 23.85, 27.59, 3.09 and 3.33 mg/g, respectively. The kinetic experiment results showed that DES-MAE has significant advantages in the extraction of six compounds. The experimental results showed that DES-MAE could obtain higher yields of target components in a short time than other methods (DES-HRE, DES-UAE and Ethanol-MAE). In addition, the target components were separated from the DES extraction solution, and the recoveries of the target compounds were in the range of 75.5%-84.1%. Therefore, this paper provides a strategy for extraction and separation, the aim of which is to obtain flavonoids from FSI efficiently. Meanwhile, this study can also be used as an alternative to the traditional methods for obtaining bioactive components from plant sources in biochemistry, food industry and pharmaceutical fields.