Pei-pei Han

Metabolomic analysis of antimicrobial mechanisms of ε-poly-L-lysine on Saccharomyces cerevisiae.

ε-Poly-L-lysine (ε-PL), a naturally occurring amino acid homopolymer, has been widely used as a food preservative. However, its antimicrobial mechanism has not been fully understood. This study investigated the antimicrobial mode of action of ε-PL on a yeast, Saccharomyces cerevisiae. When treated with ε-PL at the concentration of 500 μg/mL, cell mortality was close to 100% and the phospholipid bilayer curvature, pores, and micelles on the surface of S. cerevisiae were clearly observed by scanning electron microscopy (SEM). At the level of 200 μg/mL, ε-PL significantly inhibited the cell growth of S. cerevisiae. When treated with 50 μg/mL ε-PL, the yeast cell was able to grow but the cell cycle was prolonged. A significant increase in cell membrane permeability was induced by ε-PL at higher concentrations. Metabolomics analysis revealed that the ε-PL stress led to the inhibition of primary metabolic pathways through the suppression of the tricarboxylic acid cycle and glycolysis. It is therefore proposed that the microbiostatic effect of ε-PL at lower levels on S. cerevisiae is achieved by inducing intracellular metabolic imbalance via disruption of cell membrane functions. Moreover, the results suggested that the antimicrobial mechanism of ε-PL on S. cerevisiae can in fact change from microbiostatic to microbicidal when the concentration of ε-PL increased, and the mechanisms of these two modes of action were completely different.

Functional Properties of Protein Isolates from Caragana korshinskii Kom. Extracted by Three Different Methods

Seeking cheap, sustainable protein sources greatly facilitates in alleviating the dependence upon expensive animal-based protein in many developing countries. Caragana korshinskii Kom. offers a good alternative feedstock because of its high-content of protein, low fertilizer and pesticide requirements, excellent stress (high salty and less water) tolerance, wide adaptability, etc. The functional properties of C. korshinskii Kom. protein isolates by three different extraction methods were investigated. The extraction processes greatly influenced the physiological characteristics of protein isolates. C. korshinskii Kom. protein isolate by traditional alkaline extraction (Al-CPI) exhibited good performance on emulsifying activity index, oil and water absorption capacity, and foaming property compared to A-CPI ( C. korshinskii Kom. protein isolate by the acetone precipitation method) and TCA-CPI ( C. korshinskii Kom. protein isolate by trichloroacetic acid-acetone precipitation). The water and oil adsorption capacities of Al-CPI were observed at 4.99 and 3.45 g/g, respectively, even much higher than those of soy protein isolate (SPI) (3.94 and 2.95 g/g, respectively). The highest foaming capacity was observed by Al-CPI at 185.0%, followed by A-CPI (177.5%), TCA-CPI (142.5%), and SPI (141.9%), respectively. It has to be noted that A-CPI showed good solubility at acidic pH and excellent in vitro digestibility. After sequential pepsin-trypsin digestion, the percentage of N release of A-CPI reached up to 83.7%, which was 1.63 times that of Al-CPI (51.2%), 1.19 times that of TCA-CPI (70.1%), and slightly higher than that of the commercial SPI (82.5%). These results indicate that C. korshinskii Kom. holds great potential for application in the animal feed and food additive industry.

The physiological responses of terrestrial cyanobacterium Nostoc flagelliforme to different intensities of ultraviolet-B radiation

Nostoc flagelliforme is a pioneer organism in the desert and exerts important ecological functions. The habitats of N. flagelliforme are characterized by intense solar radiation, while the ultraviolet B (UV-B) tolerance has not been fully explored yet. To evaluate the physiological responses of N. flagelliforme to UV-B radiation, three intensities (1 W m−2, 3 W m−2 and 5 W m−2) were used, and the changes in photosynthetic pigments, cell morphology, mycosporine-like amino acids (MAAs) synthesis and cell metabolism were comparatively investigated. Under high UV-B intensity or long term radiation, chlorophyll a, allophycocyanin and phycocyanin were greatly decreased; scanning electron microscope observations showed that cell morphology significantly changed. To reduce the damage, cells synthesized a large amount of carotenoid. Moreover, three kinds of MAAs were identified, and their concentrations varied with the changes of UV-B intensity. Under 1 W m−2 radiation, cells synthesized shinorine and porphyra-334 against UV-B, while with the increase of intensity, more shinorine turned into asterine-330. Metabolite profiling revealed the contents of some cytoprotective metabolites were greatly increased under 5 W m−2 radiation. The principal component analysis showed cells exposed to UV-B were metabolically distinct from the control sample, and the influence on metabolism was particularly dependent on intensity. The results would improve the understanding of physiological responses of N. flagelliforme to UV-B radiation and provide an important theoretical basis for applying this organism to control desertification.

Effect of culture conditions on the physicochemical properties and antioxidant activities of polysaccharides from Nostoc flagelliforme

Three polysaccharides (WL-CPS-1, NaCl-CPS-1 and Glu-CPS-1) were extracted and purified from Nostoc flagelliforme under normal, salt stress and mixotrophic culture conditions respectively. Their physicochemical properties and antioxidant activities were investigated. WL-CPS-1, NaCl-CPS-1 and Glu-CPS-1 chemical composition differed in sugar and uronic acid contents, and they were composed of nine constituent monosaccharides and one uronic acid with different ratios, with the average molecular weights of 1.02 × 103, 1.12 × 103 and 1.33 × 103 kDa, respectively. They presented similar fourier transform infrared spectra, but different surface morphology, chain length and branching. Antioxidant assay showed that they all exhibited strong scavenging activity on ABTS+ and hydroxyl radicals and moderate activity on DPPH radical. Glu-CPS-1 exhibited the highest antioxidant activity suggested culture conditions could regulate the bioactivity through influencing the structure and properties. These findings demonstrated the potential application of proper regulation of culture conditions in the development of polysaccharides with high antioxidant activity.

Influence of culture conditions on extracellular polysaccharide production and the activities of enzymes involved in the polysaccharide synthesis of Nostoc flagelliforme

Culture conditions significantly influence extracellular polysaccharide (EPS) production of Nostoc flagelliforme, however, the key enzyme controlling EPS synthesis has not been fully explored yet. The influence of different culture conditions including light quality, carbon source and nitrogen source on EPS production of N. flagelliforme and activities of EPS synthesis enzymes was investigated. Three experimental groups produced higher amounts of EPS than the control group, including the carbon source group with 1.26 g L−1 NaHCO3, the nitrogen source group with 0 g L−1 NaNO3 and the light quality group with blue light. Activities of seven related enzymes phosphoglucose isomerase (PGI), fructose-1,6-bisphosphatase (FBPase), UDP-glucose pyrophosphorylase (UGPase), UDP-galactose-4-epimerase (UGE), UDP-glucose dehydrogenase (UGDH), phosphomannose isomerase (PMI), and phosphofructokinase (PFK) were significantly influenced by culture conditions. Partial least-squares analysis and correlation analysis methods were used to analyze the relationship between the activities of these enzymes and EPS production, and a correlation between the production of EPS and the activities of PGI, PMI, FBPase, UGDH, and UGPase was found under different culture conditions. Subsequent analysis of the transcription level of genes encoding the five enzymes showed genes pgi and fbp1 in three experimental groups were significantly up regulated. The results revealed PGI and FBPase might be important enzymes positively influencing the biosynthesis of N. flagelliforme EPS. The findings would be helpful to further understand the pathway of EPS biosynthesis aimed to improve the EPS production of N. flagelliforme.

Application of Sun Light Conversion Film on the Outdoor Culture of Nostoc flagelliforme

In this study, the influences of different types of sunlight conversion film (SCF) on biomass, extracellular polysaccharide (EPS), and photosynthetic pigment and protein production of Nostoc flagelliforme in outdoors cultivation were investigated. The results showed that, compared with control group, SCF 40#, 34#, 39# significantly improved the production of biomass, chlorophyll a, and phycobiliproteins; SCF 41# promoted the biomass and phycobiliproteins production but inhibited the chlorophyll a formation; all the SCFs greatly promoted the EPS production except the 34# and 47#; Although there are no significant difference between the control group and SCF 34# or 36#, SCF 34#, 36# both significantly increased the crude protein content of N. flagelliforme compared with the other SCF treatments. Particularly, both the biomass and EPS production reached the highest under the use of SCF 41#, which were increased by 20.35 and 63.15% compared with control group, respectively. This study proved that application of SCF on microalgal culture was feasible, and the results would shed light on novel culture strategies for outdoor cultivation of microalgae.

Studies on Protein Extraction from Caragana korshinskii Kom. Using Acetone Precipitation Method

Caragana korhinskii Kom is a desert shrub which belongs to genus Caragana. In this work, protein extraction from C. Korshinskii Kom using acetone precipitation method was investigated. Orthogonal experiments showed that the optimal extraction conditions were as follows: ratio of extraction buffer to tissue pounder 20:1, extraction time 7 h, ratio of acetone to supernatant 3.5:1. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that five major bands and two large diffuse bands could be found. The approximate molecular weight for the extracted proteins ranged from 25 to 66.2 kDa.