Water-Soluble Humic Materials Regulate Quorum Sensing in Sinorhizobium meliloti Through a Novel Repressor of expR.

Quorum sensing (QS) plays an important role in the growth, nodulation, and nitrogen fixation of rhizobia. In this study, we show that water-soluble humic materials (WSHM) repress the expression of the QS related genes sinI, sinR, and expR in Sinorhizobium meliloti. This decreased the production of N-acetyl homoserine lactones (AHL) and exopolysaccharides (EPS), and ultimately increased S. meliloti cell density. We also identified a novel regulator, SMc03890 (renamed QsrR), which binds directly to the expR promoter. Deletion of qsrR increased expR expression. WSHM repressed the expression of expR by augmenting the interaction between QsrR and the expR promoter; this was determined by a bacterial-one-hybrid assay. These effects of WSHM on the QS system in S. meliloti may be the underlying mechanism by which WSHM increase the symbiotic nitrogen fixation of Medicago sativa inoculated with S. meliloti. This study provides the first evidence that humic acids regulate the QS of rhizobia and suggests that WSHM could be used as fertilizers to improve the efficiency of symbiotic nitrogen fixation.

Hepatoprotective activity of total iridoid glycosides isolated from Paederia scandens (lour.) Merr. var. tomentosa.

ETHNOPHARMACOLOGICAL RELEVANCE: Currently, human liver is susceptible to injury caused by alcohol and virus infiltration, resulting in hepatitis, cirrhosis, and even hepatocellular carcinoma. Paederia scandens (Lour.) Merr. var. tomentosa (Rubiaceae) has been used as traditional medicine in Asian countries to treat jaundice, dysentery, and abdominal mass. Furthermore, the abundance of iridoid glycosides in Paederia species indicates their notable hepatoprotective potential. MATERIALS AND METHODS: Total iridoid glycosides (TG) was prepared, and constituents of TG were analyzed by HPLC. TG and silymarin (positive) were orally administered for 15 days. Then, acute liver injury rats was induced by intraperitoneally injection (i.p.) of 10% CCl4 (0.12%, v/v, dissolved in olive oil, 10 mL/kg, body weight). Rats were sacrificed at 16 h after CCl4 injection. Liver tissues and blood were collected. Serum samples were prepared to determine the activities of alanine transaminase (ALT) and aspartate transaminase (AST), whereas liver tissue sections were prepared for the purpose of examining possible liver histopathological changes. In addition, antioxidant enzyme activities in liver tissues were also evaluated. RESULTS: Our results demonstrated that TG significantly decreased the levels of AST and ALT, compared with those in control rats. In addition, pre-treatment of the rats with TG clearly alleviated their liver tissue injuries. What's more, the activities of GSH, GAT and SOD in the groups of TG-treated rats were significantly increased compared with those of rats in the control group, whereas the levels of MDA were decreased. CONCLUSIONS: Our present research indicated that TG possessed notable hepatoprotective activity via decreasing oxidative stress level in liver tissues.