Antibacterial Activity and Mechanisms of Essential Oil from Citrus medica L. var. sarcodactylis.

In this work, antibacterial activity of finger citron essential oil (FCEO, Citrus medica L. var. sarcodactylis) and its mechanism against food-borne bacteria were evaluated. A total of 28 components in the oil were identified by gas chromatography-mass spectrometry, in which limonene (45.36%), γ-terpinene (21.23%), and dodecanoic acid (7.52%) were three main components. For in vitro antibacterial tests, FCEO exhibited moderately antibacterial activity against common food-borne bacteria: Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus. It showed a better bactericidal effect on Gram-positive bacteria than Gram-negative. Mechanisms of the antibacterial action were investigated by observing changes of bacteria morphology according to scanning electron microscopy, time-kill analysis, and permeability of cell and membrane integrity. Morphology of tested bacteria was changed and damaged more seriously with increased concentration and exposure time of FCEO. FCEO showed a significant reduction effect on the growth rate of surviving bacteria and lead to lysis of the cell wall, intracellular ingredient leakage, and consequently, cell death.

Advances in antitumor polysaccharides from phellinus sensu lato: Production, isolation, structure, antitumor activity, and mechanisms.

Edible and medicinal fungi (mushrooms) are widely applied to functional foods and nutraceutical products because of their proven nutritive and medicinal properties. Phellinus sensu lato is a well-known medicinal mushroom that has long been used in preventing ailments, including gastroenteric dysfunction, diarrhea, hemorrhage, and cancers, in oriental countries, particularly in China, Japan, and Korea. Polysaccharides represent a major class of bioactive molecules in Phellinus s. l., which have notable antitumor, immunomodulatory, and medicinal properties. Polysaccharides that were isolated from fruiting bodies, cultured mycelia, and filtrates of Phellinus s. l. have not only activated different immune responses of the host organism but have also directly suppressed tumor growth and metastasis. Studies suggest that polysaccharides from Phellinus s. l. are promising alternative anticancer agents or synergizers for existing antitumor drugs. This review summarizes the recent development of polysaccharides from Phellinus s. l., including polysaccharide production, extraction and isolation methods, chemical structure, antitumor activities, and mechanisms of action.

Green synthesis of biocompatible carboxylic curdlan-capped gold nanoparticles and its interaction with protein.

This study demonstrates a facile, green strategy for the preparation of gold nanoparticles (AuNPs) from chloroauric acid (HAuCl4) using carboxylic curdlan (Cc) as both reducing and stabilizing agent. The as-prepared AuNPs are characterized by UV-vis spectroscopy, high resolution transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectrometry and Fourier transform infrared spectroscopy. The results indicated that the particle size of the AuNPs changes with variations in the reaction time and concentrations of Cc and HAuCl4. The spherical AuNPs are well dispersed, exhibiting high stability even after six months storage. The carboxylic groups (COO(-)) in the Cc molecules tend to adsorb and stabilize the surface of the AuNPs. The interaction between BSA and the Cc-capped AuNPs was investigated using fluorescence and circular dichroism spectroscopies. The results indicated that the BSA molecules adsorb on the surface of the AuNPs, without significant change in its helical structure even after conjugation with the AuNPs.

Effects of Tween 80 and pH on mycelial pellets and exopolysaccharide production in liquid culture of a medicinal fungus.

This study investigated the effects of surfactant additives and medium pH on mycelial morphology and exopolysaccharide (EPS) production in liquid culture of a valuable medicinal fungus Cordyceps sinensis Cs-HK1. In the medium containing 20 g l⁻¹ glucose and 6 g l⁻¹ peptone as the sole nitrogen source, the Cs-HK1 fungal mycelia formed smooth and spherical pellets about 1.8-mm mean diameter. The mycelial pellets became less uniform at pH (4.0-5.0) lower than the optimum (pH 6.0) or turned to filamentous form at higher pH (8-9). Surfactants added to the medium inhibited pellet formation, resulting in smaller and looser pellets. Tween 80 exhibited a remarkable promoting effect on EPS production, increasing the EPS yield more than twofold at 1.5% (w/v), which was most probably attributed to the stimulation of EPS biosynthesis and release from the fungal cells by Tween 80.

Modeling of Fusarium redolens Dzf2 mycelial growth kinetics and optimal fed-batch fermentation for beauvericin production.

Beauvericin (BEA) is a cyclic hexadepsipeptide mycotoxin with notable phytotoxic and insecticidal activities. Fusarium redolens Dzf2 is a highly BEA-producing fungus isolated from a medicinal plant. The aim of the current study was to develop a simple and valid kinetic model for F. redolens Dzf2 mycelial growth and the optimal fed-batch operation for efficient BEA production. A modified Monod model with substrate (glucose) and product (BEA) inhibition was constructed based on the culture characteristics of F. redolens Dzf2 mycelia in a liquid medium. Model parameters were derived by simulation of the experimental data from batch culture. The model fitted closely with the experimental data over 20-50 g l(-1) glucose concentration range in batch fermentation. The kinetic model together with the stoichiometric relationships for biomass, substrate and product was applied to predict the optimal feeding scheme for fed-batch fermentation, leading to 54% higher BEA yield (299 mg l(-1)) than in the batch culture (194 mg l(-1)). The modified Monod model incorporating substrate and product inhibition was proven adequate for describing the growth kinetics of F. redolens Dzf2 mycelial culture at suitable but not excessive initial glucose levels in batch and fed-batch cultures.

Modeling of Xanthophyllomyces dendrorhous growth on glucose and overflow metabolism in batch and fed-batch cultures for astaxanthin production.

An astaxanthin-producing yeast Xanthophyllomyces dendrorhous ENM5 was cultivated in a liquid medium containing 50 g/L glucose as the major carbon source in stirred fermentors (1.5-L working volume) in fully aerobic conditions. Ethanol was produced during the exponential growth phase as a result of overflow metabolism or fermentative catabolism of glucose by yeast cells. After accumulating to a peak of 3.5 g/L, the ethanol was consumed by yeast cells as a carbon source when glucose in the culture was nearly exhausted. High initial glucose concentrations and ethanol accumulation in the culture had inhibitory effects on cell growth. Astaxanthin production was partially associated with cell growth. Based on these culture characteristics, we constructed a modified Monod kinetic model incorporating substrate (glucose) and product (ethanol) inhibition to describe the relationship of cell growth rate with glucose and ethanol concentrations. This kinetic model, coupled with the Luedeking-Piret equation for the astaxanthin production, gave satisfactory prediction of the biomass production, glucose consumption, ethanol formation and consumption, and astaxanthin production in batch cultures over 25-75 g/L glucose concentration ranges. The model was also applied to fed-batch cultures to predict the optimum feeding scheme (feeding glucose and corn steep liquor) for astaxanthin production, leading to a high volumetric yield (28.6 mg/L) and a high productivity (5.36 mg/L/day).

The signaling role of extracellular ATP and its dependence on Ca2+ flux in elicitation of Salvia miltiorrhiza hairy root cultures.

The application of a polysaccharide elicitor from yeast extract, YE, to Salvia miltiorrhiza hairy root cultures induced transient release of ATP from the roots to the medium, leading to a dose-dependent increase in the extracellular ATP (eATP) level. The eATP level rose to a peak (about 6.5 nM with 100 mg l(-1) YE) at about 10 h after YE treatment, but dropped to the control level 6 h later. The elicitor-induced ATP release was dependent on membrane Ca2+ influx, and abolished by the Ca2+ chelator EGTA or the channel blocker La3+. The YE-induced H2O2 production was strongly inhibited by reactive blue (RB), a specific inhibitor of membrane purinoceptors. On the other hand, the application of exogenous ATP at 10-100 microM to the cultures also induced rapid and dose-dependent increases in H2O2 production and medium pH, both of which were effectively blocked by RB and EGTA. The non-hydrolyzable ATP analog ATPgammaS was as effective as ATP, but the hydrolyzed derivatives ADP or AMP were not so effective in inducing the pH and H2O2 increases. Our results suggest that ATP release is an early event and that eATP plays a signaling role in the elicitation of plant cell responses; Ca2+ is required for activation of the elicitor-induced ATP release and the eATP signal transduction. This is the first report on ATP release induced by a fungal elicitor and its involvement in the elicitor-induced responses in plant cells.

Perfusion culture process plus H2O2 stimulation for efficient astaxanthin production by Xanthophyllomyces dendrorhous.

A semicontinuous perfusion culture process (repeated medium renewal with cell retention) was evaluated together with batch and repeated fed-batch processes for astaxanthin production in shake-flask cultures of Xanthophyllomyces dendrorhous. The perfusion process with 25% medium renewal every 12 h for 10 days achieved a biomass density of 65.6 g/L, a volumetric astaxanthin yield of 52.5 mg/L, and an astaxanthin productivity of 4.38 mg/L-d, which were 8.4-fold, 5.6-fold, and 2.3-fold of those in the batch process, 7.8 g/L, 9.4 mg/L, and 1.88 mg/L-d, respectively. The incorporation of hydrogen peroxide (H(2)O(2)) stimulation of astaxanthin biosynthesis into the perfusion process further increased the astaxanthin yield to 58.3 mg/L and the productivity to 4.86 mg/L-d. The repeated fed-batch process with 8 g/L glucose and 4 g/L corn steep liquor fed every 12 h achieved 42.2 g/L biomass density, 36.5 mg/L astaxanthin yield, and 3.04 mg/L-d astaxanthin productivity. The lower biomass and astaxanthin productivity in the repeated fed-batch than in the perfusion process may be mostly attributed to the accumulation of inhibitory metabolites such as ethanol and acetic acid in the culture. The study shows that perfusion process plus H(2)O(2) stimulation is an effective strategy for enhanced astaxanthin production in X. dendrorhous cultures.

Hydrogen peroxide-induced astaxanthin biosynthesis and catalase activity in Xanthophyllomyces dendrorhous.

Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) in shake-flask cultures was exposed to 10-20 mmol/L H(2)O(2) at various culture stages, and the astaxanthin production was significantly increased by H(2)O(2) fed at 0 or 24 h (exponential phase), but only slightly at 48 h (near stationary phase). The astaxanthin production was enhanced most significantly with double feeding of 10 mmol/L H(2)O(2) at 0 and 24 h, reaching a cellular content of 1.30 mg/g cell and a volumetric yield of 10.4 mg/L, which were 83 and 65% higher, respectively, than those of the control (0.71 mg/g cell and 6.3 mg/L). The intracellular catalase (CAT) activity was also increased after H(2)O(2) treatment. The increases in CAT and astaxanthin of cells could be detected within 4 h of H(2)O(2) treatment. The increase in the astaxanthin content of cells was concomitant with a notable decrease in the beta-carotene content. The older yeast cells at late culture stage (120 h), due perhaps in part to their higher astaxanthin contents, were more tolerant to H(2)O(2) toxicity than the younger cells (24 h). No enhancement of the astaxanthin biosynthesis was attained when H(2)O(2) was added to the yeast culture together with a sufficient amount of exogenous CAT. The results suggest that astaxanthin biosynthesis in X. dendrorhous can be stimulated by H(2)O(2) as an antioxidative response.