Xiangtao Meng

Microwave-assisted degradation of chitosan for a possible use in inhibiting crop pathogenic fungi.

Degradation of chitosan by H(2)O(2) under microwave irradiation was investigated. The oxidative degradation of chitosan was highly accelerated by microwave irradiation under the condition of low temperature and low concentration of H(2)O(2). The degraded chitosans with low molecular weight (M(w)) were characterized by gel permeation chromatography, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray diffraction and elemental analysis. The decrease of M(w) led to transformation of crystal structure and increase of water solubility, whereas no significant chemical structure change in the backbone of chitosan was observed. Antifungal activities of chitosans with different M(w) against crop pathogenic fungi Phomopsis asparagi, Fusarium oxysoporum f. sp. Vasinfectum and Stemphylium solani were investigated at the concentrations of 100, 200 and 400 mg/L. All degraded chitosans with low M(w) exhibited enhanced antifungal activity compared with original chitosan and the chitosan of 41.2 kDa showed the highest activity. At 400 mg/L, the chitosan of 41.2 kDa inhibited growth of P. asparagi at 89.3%, stronger than polyoxin and triadimefon, the inhibitory effects of which were found to be 55.5% and 68.5%. All the results indicated that oxidative degradation under microwave irradiation was a promising technique for large-scale production of low M(w) chitosan for use in crop protection.

Molecular weight and pH effects of aminoethyl modified chitosan on antibacterial activity in vitro

Aminoethyl modified chitosan derivatives (AEMCSs) with different molecular weight (Mw) were synthesized by grafting aminoethyl group on different molecular weight chitosans and chitooligosaccharide. FTIR, (1)H NMR, (13)C NMR, elemental analysis and potentiometric titration results showed that branched polyethylimine chitosan was synthesized. Clinical Laboratory Standard Institute (CLSI) protocols were used to determine MIC for Gram-negative strain of Escherichia coli under different pH. The antibacterial activity of the derivatives was significantly improved compared with original chitosans, with MIC values against E. coli varying from 4 to 64 μg/mL depending on different Mw and pH. High molecular weight seems to be in favor of stronger antibacterial activity. At pH 7.4, derivatives with Mw above 27 kDa exhibited equivalent antibacterial activity (16 μg/mL), while oligosaccharide chitosan derivative with lower Mw (~1.4 kDa) showed decreased MIC of 64 μg/mL. The effect of pH on antibacterial activity is more complicated. An optimal pH for HAEMCS was found around 6.5 to give MIC as low as 4 μg/mL, while higher or lower pH compromised the activity. Cell integrity assay and SEM images showed evident cell disruption, indicating membrane disruption may be one possible mechanism for antibacterial activity.

Synthesis and characterization of dithiocarbamate chitosan derivatives with enhanced antifungal activity

In this study, ammonium dithiocarbamate chitosan (ADTCCS) and triethylene diamine dithiocarbamate chitosan (TEDADTCCS) derivatives were obtained respectively by mixing chitosan with carbon disulfide and ammonia (triethylenediamine). Their structures were confirmed by FT-IR, 1H NMR, XRD, DSC, SEM, and elemental analysis. Antifungal properties of them against the plant pathogenic fungi Fusarium oxysporum and Alternaria porri were investigated at concentrations ranged from 31.25 to 500 mg/L. The dithiocarbamate chitosan derivatives had enhanced antifungal activity compared with chitosan. Particularly, they showed obvious inhibitory effect on Fusarium oxysporum. At 500 mg/L, TEDADTCCS inhibited growth of F. oxysporum at 60.4%, stronger than polyoxin and triadimefon whose antifungal indexes were found to be 25.3% and 37.7%. The chitosan derivatives described here deserve further study for use in crop protection.

Application of nanoLC–MS/MS to the shotgun proteomic analysis of the nematocyst proteins from jellyfish Stomolophus meleagris

The nematocyst proteins of jellyfish Stomolophus meleagris, a complicated mixture, contain many important bioactive molecules. In present study, to gain comprehensive insight into the protein component and search some novel bioactive molecules in the nematocyst proteins, shotgun proteomic analysis of the nematocyst proteins was carried out by nano liquid chromatography tandem mass spectrometry (nanoLC-MS/MS) for the first time. Digested peptides of the nematocyst proteins were analyzed by nanoLC-MS/MS and all MS/MS spectra were then automatically searched by the SEQUEST program. A total of 181 proteins had been identified, with the molecular weight ranging from 5268.06 to 843,487.57 and the pI from 4.49 to 11.39. Bioinformatic analysis was also applied to better understand the identified proteins. In the gene ontology (GO) annotation, all the identified proteins were classified into 13, 9 and 7 groups according to biological process, cellular component and molecular function, respectively. Pathways analysis of the identified proteins was conducted with 33 corresponding pathways found. On the basis of pathways analysis, we also constructed the gene network to analyze the relationship of those genes each other, which contained enzyme-enzyme relation, protein-protein interaction and gene expression interaction.

Isolation and in vitro partial characterization of hemolytic proteins from the nematocyst venom of the jellyfish Stomolophus meleagris

Jellyfish venom contains various toxins and can cause itching, edema, muscle aches, shortness of breath, blood pressure depression, shock or even death after being stung. Hemolytic protein is one of the most hazardous components in the venom. The present study investigated the hemolytic activity of the nematocyst venom from jellyfish Stomolophus meleagris. Anion exchange chromatography, DEAE Sepharose Fast Flow, and gel filtration chromatography, Superdex200 had been employed to isolate hemolytic proteins from the nematocyst venom of jellyfish S. meleagris. Hemolysis of chicken red blood cells was used to quantify hemolytic potency of crude nematocyst venom and chromatography fractions during the purification process. Native-PAGE profile displayed one protein band in the purified hemolytic protein (SmTX); however, two protein bands with apparent molecular weights of ≈ 45 kDa and 52 kDa were observed in the reducing SDS-PAGE analysis. Approximately 70 μg/mL of SmTX caused 50% hemolysis (HU50) of the erythrocyte suspension. The hemolytic activity of SmTX was shown to be temperature and pH dependent, with the optimum temperature and pH being 37°C and pH 5.0. The present study is the first report of isolation and partial characterization of hemolytic proteins from the nematocyst venom of the jellyfish S. meleagris. The mechanism of the hemolytic activity of SmTX is not clear and deserves further investigation.

Isolation, identification and characterization of a novel antioxidant protein from the nematocyst of the jellyfish Stomolophus meleagris.

Reactive oxygen species (ROS) can damage the lipids, proteins and DNA when produced excessively in cells. Here, we describe the isolation and identification of a novel antioxidant protein named SmP90 from the nematocyst of jellyfish Stomolophus meleagris by 50% ammonium sulfate precipitation and gel filtration chromatography, superdex75. HPLC and SDS-PAGE analysis revealed >95% purity of SmP90 with apparent molecular weight of 90 kDa, approximately. The identification of SmP90 was confirmed by both N-terminal amino acids sequencing, with the sequences of NLDTPYCFYSGDYGG, and peptide mass fingerprint (PMF) analysis by MALDI-TOF-MS. However, no known protein had been completely matched in the database, which indicated that SmP90 might be a novel protein. The antioxidant assay result showed that it had strong superoxide anion radical-scavenging activity with the half-scavenging concentration (EC(50)) of about 16 μg/mL. Therefore, the present study is the first time to demonstrate a high efficient method of isolating a novel antioxidant protein from the nematocyst of jellyfish S. meleagris.

Design, synthesis and antimicrobial activity of 6-N-substituted chitosan derivatives.

Three novel 6-N-substituted chitosan derivatives were designed and synthesised and characterized by FTIR and NMR. The degree of substitution was calculated by elemental analysis results. The antimicrobial activities of the target compounds were evaluated by twofold serial broth dilution method and poisoned food technique. The antifungal activities of 6-aminoethylamino-6-deoxy chitosan (3), 6-butylamino-6-deoxy chitosan (4) and 6-pyridyl-6-deoxy chitosan (5) were significantly increased against Rhizoctonia cerealis, Fusarium oxysporum and Botrytis cinerea, and the inhibition rate ranged from 22.48% to 63.56% at the concentration of 0.2mg/mL. The compound 3 had better antibacterial activities than chitosan, and the minimum inhibition concentration of which ranged between 6.25 and 25mg/L against gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis and Bacillus anthracis) and gram-negative bacteria (Escherichia coli, Salmonella typhi). The antibacterial activities of 6-N-substituted chitosan tended to increase with the increase of the number of -NH2 group.