Rhizobium trifolii capsular polysaccharide: a novel biopolymer with striking physical properties

The physical properties of the capsular polysaccharide of Rhizobium Trifolii (CPS) were investigated. Viscosity measurements provided information about the hydrodynamic volume of single coils, the perturbation of solvent flow and the shear-thinning behaviour of concentrated solutions. Changes in chain geometry and the development of an intermolecular network as a function of temperature were monitored using the techniques of optical rotation and dynamic oscillation. Finally, analysis of calorimetric thermograms elucidated the type of interactions between CPS and the bacterial levan. Overall, the Rhizobium polysaccharide was found to form thermally-reversible gels at an extremely low 'minimum critical gelling concentration' (c_o∼ 0.35gl^-1). At temperatures above the gel melting point (∼ 48°C), however, the compact polymer coils entangled at comparatively high concentrations (about 60 times higher than c_o). In the presence of a highly branched levan, the thermal stability of ordered CPS structures increased as a consequence of thermodynamic incompatibility between the two polymers.     

地衣芽孢杆菌产Levan果聚糖发酵条件的优化

通过单因素试验(培养基用水、碳源、氮源、培养温度和培养基初始pH值)和正交试验对地衣芽孢杆菌(Bacillus licheniformis)8-37-0-1发酵产生Levan果聚糖的培养基组成及培养条件进行优化,采用苯酚-硫酸法测定多糖含量。结果表明：以蔗糖100g/L、牛肉膏1.0g/L、酵母粉0.6g/L、K2HPO4 3.0g/L、KH2PO4 3.0g/L、NaCl 1.0g/L、MgSO4·7H2O 0.2g/L、FeSO4·7H2O 0.001g/L,自来水配制,培养基初始pH5.0,30℃培养8-37-0-1菌株24h,Levan果聚糖产量达到最高值41.7g/L,约是未优化时的5.0倍。     

A Fructan Exohydrolase from Maize Degrades Both Inulin and Levan and Co-Exists with 1-Kestotriose in Maize

Enzymes with fructan exohydrolase (FEH) activity are present not only in fructan-synthesizing species but also in non-fructan plants. This has led to speculation about their functions in non-fructan species. Here, a cell wall invertase-related Zm-6&1-FEH2 with no “classical” invertase motif was identified in maize. Following heterologous expression in Pichia pastoris and in Nicotiana benthamiana leaves, the enzyme activity of recombinant Zm-6&1-FEH2 displays substrate specificity with respect to inulin and levan. Subcellular localization showed Zm-6&1-FEH2 exclusively localized in the apoplast, and its expression profile was strongly dependent on plant development and in response to drought and abscisic acid. Furthermore, formation of 1-kestotriose, an oligofructan, was detected in vivo and in vitro and could be hydrolyzed by Zm-6&1-FEH2. In summary, these results support that Zm-6&1-FEH2 enzyme from maize can degrade both inulin-type and levan-type fructans, and the implications of the co-existence of Zm-6&1-FEH2 and 1-kestotriose are discussed.     

解淀粉芽孢杆菌果聚糖的化学修饰与抗氧化、抗肿瘤活性研究

对解淀粉芽孢杆菌果聚糖(L)进行乙酰化、磺酰化、硫酸化修饰,对获得的相应化学修饰产物(YL,HL,SL)进行抗氧化与抗肿瘤活性研究。发现经化学修饰后,解淀粉芽孢杆菌果聚糖的抗氧化性与抗肿瘤活性显著提高(p<0.05),不同化学修饰的影响不同。各果聚糖通过ABTS自由基清除能力、DPPH自由基清除能力和铁还原力测试的抗氧性顺序为SL>HL>YL>L,硫酸化修饰产物的抗氧化效果最明显。各果聚糖对对宫颈癌细胞Hela的抑制活性顺序为YL>HL>SL>L,乙酰化修饰产物的抗肿瘤活性效果最明显。上述结果说明化学修饰对微生物多糖的功能活性提升具有积极的作用。      

Immobilization of amyloglucosidase on polystyrene anion exchange resin I. preparation and properties

Amyloglucosidase (exo‐1,4‐ α‐D‐glucosidase, E C 3.2. 1.3) was coupled to glutaraldehyde activated Indion 48‐R (a cross‐linked macroporous anion exchanger) by Schiff base reaction. The bound enzyme exhibited 60–70% activity of the free enzyme. Substrate concentrations as high as 32% (w/w) liquefied tapioca starch could be quantitatively converted into 96–98% (w/w) dextrose in 24 h at 50°C and pH 4.5. Though immobilization lowered the temperature optimum to 50–60°C from 65°C for the free enzyme, it increased the temperature stability. However, there was no change either in the pH optimum or pH stability after immobilization. In batch operations, the immobilized preparation showed a half life of 32 and 12 days at 50°C and 60°C respectively.     

Antipathogenic activity and preservative effect of levan (β‐2,6‐fructan), a multifunctional polysaccharide

The objective of this study was to investigate the antibacterial activity of levan compounds, including high‐molecular‐weight levan, low‐molecular‐weight levan and difructose dianhydride IV (DFA IV). The levans exhibited broad antibacterial spectra against foodborne pathogenic bacteria, in a concentration‐dependent manner. From comparison with simple saccharides, often regarded as by‐products of levan production, it turned out that the antibacterial activity of levans was primarily caused by themselves. The strongest effect was observed with low‐molecular‐weight levan as compared to the others, and oligosaccharides as well. The low‐molecular‐weight levan was therefore applied to bread making. The bread samples inoculated with pathogenic bacteria were divided into two groups: bread with sugar alone (control) and bread with both sugar and levan (treatment). It was found from the in situ test that the viability of pathogenic bacteria in bread was reduced by the addition of low‐molecular‐weight levan. Therefore, levan compounds have potential as alternative sweeteners for reduction in pathogenic contamination.     

Effect of Irradiation on Structural Changes of Levan

Levan, as a biocompatible and renewable biopolymer with anticancer properties, is a promising candidate for a wide range of applications in various fields of industry. However, in the literature, there is a lack of information about its behavior under the influence of UV irradiation, which may limit its potential application, including medical science. Therefore, this study describes the effects of irradiation on the structural properties of levan. This type of fructan was subjected to stability tests under radiation conditions using LED and polychromatic lamps. The results showed that the photodegradation of levan irradiated with a polychromatic light occurs faster and more efficiently than the photodegradation of levan irradiated with an LED lamp. Furthermore, AFM analysis showed that the surface became smoother after irradiation, as evidenced by decreasing values of roughness parameters. Moreover, UV irradiation causes the decrease of total surface free energy and both its components in levan; however, more significant changes occur during irradiation of the sample with a polychromatic lamp.     

One-pot conversion of levan prepared from Serratia levanicum NN to difructose anhydride IV by Arthrobacter nicotinovorans levan fructotransferase

The newly established difructose anhydride IV (DFA IV) production system is comprised of the effective production of levan from sucrose by Serratia levanicum NN, the conversion of the levan into DFA IV by levan fructotransferase from Arthrobacter nicotinovorans GS-9, which is highly expressed in an Escherichiacoli transformant, and a practical purification step. The chemical properties of DFA IV were also investigated.     

微生物levan果聚糖及其益生功能研究进展

Levan果聚糖是一种主要以β-(2,6)糖苷键作为主链,少量β-(2,1)糖苷键作为支链的天然同型多糖。自然界中果聚糖主要来源于微生物果聚糖蔗糖酶催化蔗糖聚合而成。由于levan具备很多重要的生物学性能,如抗肿瘤、降血糖、降血脂等,从而在生物医学、食品和制药等领域的开发利用具有巨大的潜力。本文介绍了levan的性质以及levan利用果聚糖蔗糖酶催化的生物合成途径,对包括促进益生菌增殖、抑制有害菌生长、激活免疫因子、降血糖、降血脂、抗肿瘤以及抗氧化的益生功能进行了综述,并分析了目前levan存在的挑战,为后续levan潜在的商业化价值提供科研思路。