Impact of a Potent Strain of Plant Growth-Promoting Bacteria (PGPB), Bacillus subtilis S1 on Bacterial Community Composition, Enzymatic Activity, and Nitrogen Content in Cucumber Rhizosphere Soils.

Antagonistic bacterial strains from Bacillus spp. have been widely studied and utilized in the biocontrol of phytopathogens and the promotion of plant growth, but their impacts on the rhizosphere microecology when applied to crop plants are unclear. Herein, the effects of applying the antagonistic bacterium Bacillus subtilis S1 as a biofertilizer on the rhizosphere microecology of cucumbers were investigated. In a pot experiment on cucumber seedlings inoculated with S1, 3124 bacterial operational taxonomic units (OTUs) were obtained from the rhizosphere soils using high-throughput sequencing of 16S rRNA gene amplicons, and the most abundant phylum was Proteobacteria that accounted for 49.48% in the bacterial community. S1 treatment significantly reduced the abundances of soil bacterial taxa during a period of approximately 30 days but did not affect bacterial diversity in the rhizosphere soils of cucumbers. The enzymatic activities of soil nitrite reductase (S-Nir) and dehydrogenase (S-DHA) were significantly increased after S1 fertilization. However, the activities of soil urease (S-UE), cellulase (S-CL), and sucrase (S-SC) were significantly reduced compared to the control group. Additionally, the ammonium- and nitrate-nitrogen contents of S1-treated soil samples were significantly lower than those of the control group. S1 fertilization reshaped the rhizosphere soil bacterial community of cucumber plants. The S-CL activity and nitrate-nitrogen content in rhizosphere soil affected by S1 inoculation play important roles in altering the abundance of rhizosphere soil microbiota.

Construction, Characterization, and Application of an Ammonium Transporter (AmtB) Deletion Mutant of the Nitrogen-Fixing Bacterium Kosakonia radicincitans GXGL-4A in Cucumis sativus L. Seedlings.

Nitrogen is an important factor affecting crop yield, but excessive use of chemical nitrogen fertilizer has caused decline in nitrogen utilization and soil and water pollution. Reducing the utilization of chemical nitrogen fertilizers by biological nitrogen fixation (BNF) is feasible for green production of crops. However, there are few reports on how to have more ammonium produced by nitrogen-fixing bacteria (NFB) flow outside the cell. In the present study, the amtB gene encoding an ammonium transporter (AmtB) in the genome of NFB strain Kosakonia radicincitans GXGL-4A was deleted and the △amtB mutant was characterized. The results showed that deletion of the amtB gene had no influence on the growth of bacterial cells. The extracellular ammonium nitrogen (NH4+) content of the △amtB mutant under nitrogen-free culture conditions was significantly higher than that of the wild-type strain GXGL-4A (WT-GXGL-4A), suggesting disruption of NH4+ transport. Meanwhile, the plant growth-promoting effect in cucumber seedlings was visualized after fertilization using cells of the △amtB mutant. NFB fertilization continuously increased the cucumber rhizosphere soil pH. The nitrate nitrogen (NO3-) content in soil in the △amtB treatment group was significantly higher than that in the WT-GXGL-4A treatment group in the short term but there was no difference in soil NH4+ contents between groups. Soil enzymatic activities varied during a 45-day assessment period, indicating that △amtB fertilization influenced soil nitrogen cycling in the cucumber rhizosphere. The results will provide a solid foundation for developing the NFB GXGL-4A into an efficient biofertilizer agent.

Three new flavonol triglycosides from Derris trifoliata.

Three new flavonol triglycosides, kaempferol-3-O-alpha-L-rhamnopyranosyl-(1 --> 6)-beta-D-glucopyranosyl-(1 --> 3)-beta-D-glucopyranoside (1), quercetin-3-O-alpha-L-rhamnopyranosyl-(1 --> 6)-beta-D-glucopyranosyl-(1 --> 3)-beta-D-glucopyranoside (2), quercetin-3-O-alpha-L-rhamnopyranosyl-(1 --> 6)-beta-D-glucopyranosyl-(1 --> 2)-beta-D-glucopyranoside (3), together with the two known flavonol glycosides, kaempferol-3-O-alpha-L-rhamnopyranosyl-(1 --> 6)-beta-D-glucopyranoside and kaempferol-3-O-alpha-L-rhamnopyranosyl-(1 --> 6)-beta-D-glucopyranosyl-(1 --> 2)-beta-D-glucopyranoside, were isolated from the aerial parts of Derris trifoliata. Their structures were determined on the basis of chemical and spectroscopic analyses.

A new dihydrochalcone from dragon's blood, red resin of Dracaena cochinchinensis.

A new dihydrochalcone, 4'-hydroxy-4,2'-dimethoxy-dihydrochalcone, was isolated from Chinese dragon's blood, the red resin of Dracaena cochinchinensis. Its structure was established by spectrum analysis.

[Rotenoids from Derris trifoliata].

Five rotenoids named dehydrodeguelin, dehydrorotenone, 12a-hydroxy rotenone, tephrosin and 12alphabeta-hydroxyrot-2'-enonic acid were isolated from aerial parts of Derris trifoliata. All these compounds were isolated from this plant for the first time.

A new acylated flavonol glycoside from Derris triofoliata.

A new acylated flavonol glycoside, kaempferol 3-O-[(6''''-feruloyl)-beta-D-glucopyranosyl-(1 --> 3)]-[alpha-L-rhamnopyranosyl-(1 --> 6)]-beta-D-glucopyranoside and two known cyclolignan glycosides, (+)-lyoniresinol-3alpha-O-beta-D-glucopyranoside and ( - )-lyoniresinol-3alpha-O-beta-D-glucopyranoside were isolated from n-BuOH extracts of the aerial parts of Derris triofoliata, their structures were determined from spectroscopic and chemical evidences.

A new triterpenoid: taraxerol-3-beta-O-tridecyl ether from Derris triofoliata.

The new triterpenoid taraxerol-3-beta-O-tridecyl ether was isolated from the aerial part of Derris triofoliata. The structure was established on the basis of spectral data.