Shi-gang Shen

Comparison of bacterial community structures of terrestrial cyanobacterium Nostoc flagelliforme in three different regions of China using PCR-DGGE analysis

Filamentous Nostoc flagelliforme form colloidal complex, with beaded cells interacting with other bacteria embedded in the complex multilayer sheath. However, the species of bacteria in the sheath and the interaction between N. flagelliforme and associated bacteria remain unclear. In this study, PCR-denaturing gradient gel electrophoresis (DGGE) was used to investigate the bacterial communities of N. flagelliforme from three regions of China. DGGE patterns showed variations in all samples, exhibiting 25 discrete bands with various intensities. The diversity index analysis of bands profiles suggested the high similarity of bacterial communities to each other but also the dependence of microbial composition on each location. Phylogenetic affiliation indicated that the majority of the sequences obtained were affiliated with Actinobacteria, Cyanobacteria, Proteobacteria, Acidobacteria, Bacteroidetes, of which Cyanobacteria was dominant, followed the Proteobacteria. Members of the genus Nostoc were the most abundant in all samples. Rhizobiales and Actinobacteria were identified, whereas, Craurococcus, Caulobacter, Pseudomonas, Terriglobus and Mucilaginibacter were also identified at low levels. Through comparing the bacterial composition of N. flagelliforme from different regions, it was revealed that N. flagelliforme could facilitate the growth of other microorganisms including both autotrophic bacteria and heterotrophic ones and positively contributed to their harsh ecosystems. The results indicated N. flagelliforme played an important role in diversifying the microbial community composition and had potential application in soil desertification.

The relationship between monosaccharide composition of extracellular polysaccharide and activities of related enzymes in Nostoc flagelliforme under different culture conditions

The relationship between monosaccharide composition of Nostoc flagelliforme extracellular polysaccharide (EPS) and activities of EPS synthesis enzymes under various carbon sources, nitrogen sources and light culture condition was investigated. Culture conditions showed significant influences on both monosaccharide composition and related enzyme activities. Under both carbon and nitrogen sources conditions, mannose mole percentage was increased with the increase of initial mole ratio of C/N and positively related to fructose-1, 6-bisphosphatase activity, and glucuronic acid and galactose mole percentages were positively correlated with UDP-glucose dehydrogenase, while arabinose and rhamnose mole percentages were negatively associated with UDP-glucose pyrophosphorylase. Different correlation between monosaccharide composition and enzymes activity from carbon and nitrogen sources conditions was found under light condition. These findings will be helpful to establish a novel fermentation process aimed to produce the N. flagelliforme EPS with desired monosaccharide composition.

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.