Quorum sensing (QS) is a system of cell-to-cell communication by means of intercellular signaling molecules to coordinate a set of targeted gene expression or repression in many Gram-negative bacteria; it plays important roles for bacteria in adaptation to adverse environmental conditions. In this study, we first demonstrated that Microcystis aeruginosa PCC-7820 could produce QS-related signal acylated homoserine lactones (AHLs) among the metabolite of axenic M. aeruginosa, based on bioassay and liquid chromatography-mass spectrometry (LC-MS) analysis. The concentration of the AHLs in the culture medium was cell density dependent and reached a maximum of 18 nM at 1.03 × 10(7) cells mL(-1), 30 days after inoculation. The regulation mechanism of QS in M. aeruginosa and its possible role in bloom formation are discussed.
Eleutherococcus senticosus Maxim. belongs to the Araliaceae family. Phytochemical studies reveal that E. senticosus leaves contain triterpene glycosides along with organic acid derivatives and flavonoid compounds. It is believed that E. senticosus is similar to ginseng because they come from same family and both contain triterpene saponins. E. senticosus leaves have been developed as a functional beverage called ci-wu-jia tea in recent years. Triterpene glycosides are difficult to identify by ultraviolet (UV) detection and contents of these compounds are low in E. senticosus leaves. In this study, a sensitive ultra-high performance liquid chromatographic (UHPLC) method combining UV and tandem mass spectrometry (MS/MS) was developed to characterize the triterpene glycosides from E. senticosus leaves and related commercial products. Fragmentation patterns of three sub-groups of triterpene glycosides in E. senticosus leaves were investigated. Additionally, fragmentation pathways and UV characteristics of organic acid derivatives and flavonoids were also characterized. A compound screening library, including 241 compounds reported in the literature, was created and used to confirm the compounds in the samples. In this study, a total of 24 samples, including 13 plant samples of E. senticosus and 11 ci-wu-jia tea products, were analyzed. Out of the 11 commercial products, three products were discovered to contain green tea (Camellia sinensis) that was considered to be an adulterant since it was not an ingredient on the labels. The developed UHPLC-UV-MS/MS analytical method combined with the UNIFI processing method can simultaneously characterize organic acid derivatives, flavonoids, and triterpene saponins from E. senticosus. It provides a simple and sensitive way to perform quality control of E. senticosus and related ci-wu-jia tea products.
Summary
Cyanobacteria, a phylum of bacteria that obtains energy by oxygenic photosynthesis, can be found in almost every terrestrial and aquatic habitat on Earth and play an important role in global carbon and oxygen cycles and as food sources for fish. However, common bloom‐forming cyanobacteria in the genus Microcystis produce microcystins that are toxic to human beings and aquatic animals and can have disastrous effects in aquatic ecosystems.
Algal species follow seasonal successions of bloom formation and Microcystis spp. have been reported to be more competitive than other algal species in lakes. However, so far there has been no clear demonstration of competition among Microcystis species.
By means of growth experiments, we demonstrate that two common cyanobacterial species Microcystis aeruginosa FACHB‐905 and Microcystis flos‐aquae FACHB‐1028, which are the dominant toxigenic species in Lake Taihu, exhibit a competitive relationship under coculture condition, the former outcompeting the latter.
We show that M. aeruginosa is a superior competitor to M. flos‐aquae regardless of temperature, nutrients and initial abundance ratios. Moreover, both unicultured filtrates of M. aeruginosa and cocultured filtrates of both species strongly inhibit the growth of M. flos‐aquae.
An analysis using gas chromatography mass spectrometry of extracts of filtrates from unicultures and cocultures indicates that some extracellular allelopathic compounds produced by M. aeruginosa, such as D‐limonene and 1‐chlorine heptacosane, might play important roles in competition among the species.
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