Effect of the environmental factors on diketopiperazine cyclo(Pro-Phe) production and antifungal activity of Bacillus amyloliquefaciens Q-426

Bacillus amyloliquefaciens Q-426 with strong antifungal activity was isolated from the compost samples in Dalian of China. Four kinds of diketopiperazines were extracted from the strain including cyclo(Pro-Phe) (cPP), which had cyclo(L-Pro-L-Phe), cyclo(D-Phe-L-Pro), cyclo(D-Pro-D-Phe) and cyclo(L-Pro-D-Phe) isomers. Results showed that (1) cPP production reached the maximum at 12 h and then maintained the constant yield; (2) cPP maintained a stable production in a wide temperature range of 31-42 degrees C; (3) cPP production were quite different for various carbon sources because of the different growth rate of the strain; (4) cPP maintained a higher level yield in neutral and weakly alkaline environment (pH 6-10) than acid (pH 3-5) environment. Moreover, cPP played a negative effect on the synthesis of antifungal substance when the bacteria maintained a good growth, and the previous studies found that cPP showed a positive response to biosensors which were used to detect signal molecules. Based on these studies, diketopiperazines were suspected as the signal molecule of B. amyloliquefaciens Q-426

Potential Pharmacological Resources: Natural Bioactive Compounds from Marine-Derived Fungi

In recent years, a considerable number of structurally unique metabolites with biological and pharmacological activities have been isolated from the marine-derived fungi, such as polyketides, alkaloids, peptides, lactones, terpenoids and steroids. Some of these compounds have anticancer, antibacterial, antifungal, antiviral, anti-inflammatory, antioxidant, antibiotic and cytotoxic properties. This review partially summarizes the new bioactive compounds from marine-derived fungi with classification according to the sources of fungi and their biological activities. Those fungi found from 2014 to the present are discussed

Widespread Existence of Quorum Sensing Inhibitors in Marine Bacteria: Potential Drugs to Combat Pathogens with Novel Strategies

Quorum sensing (QS) is a phenomenon of intercellular communication discovered mainly in bacteria. A QS system consisting of QS signal molecules and regulatory protein components could control physiological behaviors and virulence gene expression of bacterial pathogens. Therefore, QS inhibition could be a novel strategy to combat pathogens and related diseases. QS inhibitors (QSIs), mainly categorized into small chemical molecules and quorum quenching enzymes, could be extracted from diverse sources in marine environment and terrestrial environment. With the focus on the exploitation of marine resources in recent years, more and more QSIs from the marine environment have been investigated. In this article, we present a comprehensive review of QSIs from marine bacteria. Firstly, screening work of marine bacteria with potential QSIs was concluded and these marine bacteria were classified. Afterwards, two categories of marine bacteria-derived QSIs were summarized from the aspects of sources, structures, QS inhibition mechanisms, environmental tolerance, effects/applications, etc. Next, structural modification of natural small molecule QSIs for future drug development was discussed. Finally, potential applications of QSIs from marine bacteria in human healthcare, aquaculture, crop cultivation, etc. were elucidated, indicating promising and extensive application perspectives of QS disruption as a novel antimicrobial strategy

Selective Removal of H₂S from Biogas Using Solid Amine-Based “Molecular Basket” Sorbent

Biogas is an important renewable energy source, but its ppm-level hydrogen sulfide (H₂S) component must be removed from the gas mixture dominated by CO₂ and CH₄. In this work, a tertiary-amine-based “molecular basket” sorbent with a mesoporous silica as support was found to be effective for the selective hydrogen sulfide (H₂S) removal from gas mixtures simulating biogas with a high CO₂ concentration up to 40 vol %. Polyallylamine (PA), polyethylenimine (PEI), and tetramethyl hexanediamine (TMHDA) were used as primary, secondary, and tertiary amines to prepare the SBA-15 supported sorbents, respectively, and their H₂S sorption performances were evaluated in a flow system in the absence and presence of CO₂. The tertiary-amine-based sorbent, TMHDA/SBA-15, can selectively remove H₂S in the presence of CO₂, and the highest sorption capacity was achieved at 15 wt % TMHDA loading which is close to its monolayer coverage on the surface. More importantly, about 90% of the capacity could be maintained on TMHDA/SBA-15 even with the CO₂ concentration as high as 40 vol %. The H₂S sorption on TMHDA/SBA-15 fitted with the Langmuir adsorption isotherm well although the estimated adsorption heat with the van’t Hoff equation is relatively low. Characterization using N₂ physisorption, FT-IR, and XPS demonstrated that the TMHDA is dispersed within the pore channels through the interaction between amine and silanol groups on the surface of SBA-15. The TMHDA/SBA-15 sorbents showed a good regenerability under a mild regeneration condition (e.g., 110 °C), the capacity of which was not impeded by other components in biogas such as CH₄ and H₂O

Effects of critical medium components on the production of antifungal lipopeptides from Bacillus amyloliquefaciens Q-426 exhibiting excellent biosurfactant properties

In this study, influence of three critical parameters nitrogen sources, initial pH and metal ions was discussed in the production of antifungal lipopeptides from Bacillus amyloliquefaciens Q-426. The results revealed that lipopeptide biosynthesis might have relations with the population density of strain Q-426 and some special amino acids. Also, the alkali-resistant strain Q-426 could grow well in the presence of Fe2+ ions below 0.8 M l(-1) and still maintain the competitive advantage below 0.2 M l(-1). Moreover, lipopeptides exhibited significant inhibitory activities against Curvularia lunata (Walk) Boed even at the extreme conditions of temperature, pH and salinity. Finally, biosurfactant properties of lipopeptides mixture were evaluated by use with totally six different methods including bacterial adhesion to hydrocarbons assay, lipase activity, hemolytic activity, emulsification activity, oil displacement test and surface tension measurement. The research suggested that B. amyloliquefaciens Q-426 may have great potential in agricultural and environmental fields.In this study, influence of three critical parameters nitrogen sources, initial pH and metal ions was discussed in the production of antifungal lipopeptides from Bacillus amyloliquefaciens Q-426. The results revealed that lipopeptide biosynthesis might have relations with the population density of strain Q-426 and some special amino acids. Also, the alkali-resistant strain Q-426 could grow well in the presence of Fe2+ ions below 0.8 M l(-1) and still maintain the competitive advantage below 0.2 M l(-1). Moreover, lipopeptides exhibited significant inhibitory activities against Curvularia lunata (Walk) Boed even at the extreme conditions of temperature, pH and salinity. Finally, biosurfactant properties of lipopeptides mixture were evaluated by use with totally six different methods including bacterial adhesion to hydrocarbons assay, lipase activity, hemolytic activity, emulsification activity, oil displacement test and surface tension measurement. The research suggested that B. amyloliquefaciens Q-426 may have great potential in agricultural and environmental fields

Green Fluorescent Protein (GFP)-Based Overexpression Screening and Characterization of AgrC, a Receptor Protein of Quorum Sensing in Staphylococcus aureus

Staphylococcus aureus AgrC is an important component of the agr quorum-sensing system. AgrC is a membrane-embedded histidine kinase that is thought to act as a sensor for the recognition of environmental signals and the transduction of signals into the cytoplasm. However, the difficulty of expressing and purifying functional membrane proteins has drastically hindered in-depth understanding of the molecular structures and physiological functions of these proteins. Here, we describe the high-yield expression and purification of AgrC, and analyze its kinase activity. A C-terminal green fluorescent protein (GFP) fusion to AgrC served as a reporter for monitoring protein expression levels in real time. Protein expression levels were analyzed by the microscopic assessment of the whole-cell fluorescence. The expressed AgrC-GFP protein with a C-terminal His-tagged was purified using immobilized metal affinity chromatography (IMAC) and size exclusion chromatography (SEC) at yields of ≥10 mg/L, following optimization. We also assessed the effects of different detergents on membrane solubilization and AgrC kinase activity, and polyoxyethylene-(23)-lauryl-ether (Brij-35) was identified as the most suitable detergent. Furthermore, the secondary structural stability of purified AgrC was analyzed using circular dichroism (CD) spectroscopy. This study may serve as a general guide for improving the yields of other membrane protein preparations and selecting the appropriate detergent to stabilize membrane proteins for biophysical and biochemical analyses

High-Efficiency Reducing Strain for Producing Selenium Nanoparticles Isolated from Marine Sediment

Selenium nanoparticles (SeNPs) are all important for research because they exhibit a higher degree of absorption and lower toxicity than that of their organic and inorganic forms. At present, there are few reports on marine strains that can reduce Se(IV) to generate Se(0). In this study, a strain that reduces sodium selenite to SeNPs with high efficiency was screened from 40 marine strains. The SeNPs-S produced by the whole cells and SeNPs-E produced by the extracellular extract were characterized by FTIR, UV, Raman, XRD and SEM. Based on the results, the two kinds of SeNPs exhibited obvious differences in morphology, and their surfaces were capped with different biomacromolecules. Due to the difference in shape and surface coating, opposite results were obtained for the antibacterial activity of SeNPs-S and SeNPs-E against Gram-positive and Gram-negative bacteria. Both SeNPs-S and SeNPs-E exhibited no obvious cytotoxicity at concentrations up to 100 μg/mL, but SeNPs-E retained lower cytotoxicity when its concentration increased to 200 μg/mL. This is the first report on the detailed difference between the SeNPs produced by whole cells and cell extracts

Quantitative analysis of protein orientation in membrane environments by kinase activity

AgrC is an integral membrane receptor protein with histidine kinase activity in the accessory gene regulator (agr) quorum-sensing system of Staphylococcus aureus. In this study, proteoliposomes were used as a model to investigate AgrC orientation. Many approaches have been described to determine membrane protein orientation, but they are often complicated and time consuming. In this study, AgrC orientation in liposomes was determined by thiol-reactive reagent labeling and a kinase activity assay. Our results suggest use of a kinase activity assay could get an accurate percentage of functional protein orientation and only cost nearly one-sixth of the time compared with the method based on thiol-reactive reagent labeling. We present an effective and rapid method for determining the orientation of membrane protein kinases like AgrC. (C) 2015, The Society for Biotechnology, Japan. All rights reserved