开发未可培养微生物技术的研究进展

细菌的"活的非可培养状态"(VBNC, viable but nonculturable)发现于20世纪80年代,处于此状态的细菌不但丧失了在培养基上生长繁殖的能力,而且具有与原菌相似的致病性,成为可以逃避检测的"隐性"传染源,对周围的环境及人类安全构成潜在威胁.作为公认的未可培养微生物,它一直是预防医学、流行病学、微生物生态学以及公共卫生检验检疫方面研究的热点问题之一.现代分子生物学技术和基因组学的深入研究,为开发环境中的未可培养微生物提供了新的研究方法和机遇.其中遗传指纹图谱技术、宏基因组技术显示出一定的优势,同时,随着各种细菌的非可培养状态的实验室模型已日臻成熟,这为开发和利用未可培养微生物资源提供了新的研究思路.     

葡萄果粒表皮酵母菌多样性研究

从新疆、甘肃、陕西、宁夏、山东主要酿酒葡萄产区收集葡萄果粒并分离得到酵母258株,利用26S rDNA的D1/D2区序列分析并结合形态学、生理学特征对这些菌株进行了分类学研究,探讨了这些地区葡萄果粒表皮酵母的物种多样性及其分布.共鉴定出13属26种,其中优势属为汉逊酵母属Hanseniaspora(5种),假丝酵母属Candida(4种),毕赤酵母属Pichia(4种)和伊萨酵母属Issatchenkia(2种).对分离自不同地域的同种内不同菌株进行了D1/D2序列分析比较,以探讨不同地理起源地酵母种内序列稳定性及其变异.     

Change of bacterial communities in sediments along Songhua River in Northeastern China after a nitrobenzene pollution event

More than 100 tons of nitrobenzene and related compounds were released into Songhua River due to the explosion of an aniline production factory in November, 2005. Sediment samples were taken from the heavily polluted drainage canal, one upstream and three downstream river sites. The change of bacterial community structures along the river was studied by denaturing gradient gel electrophoresis (DGGE) and cloning and sequencing of 16S rRNA genes with five clone libraries constructed and 101 sequences acquired representing 172 clones. Both DGGE profiles and sequences of 16S rRNA genes from clone libraries demonstrated that the contaminated drainage canal and three downstream river sites were similar in that all had Betaproteobacteria , mainly grouped into Comamonadaceae , as the dominant group of bacteria, and all had Firmicutes , primarily as Clostridium spp. These results suggest that these latter two groups of bacteria may play potential roles in degradation and detoxification of nitrobenzene in the present contaminated river environments.     

Telomere capping in Drosophila: dealing with chromosome ends that most resemble DNA breaks

Telomere caps prevent chromosome ends from being recognized as DNA double-strand breaks (DSBs). Unlike most organisms studied, the telomere-capping function of Drosophila does not require a specific sequence. Without this sequence component, Drosophila telomeres most resemble DNA breaks and, thus, represent a simpler system for the study of telomere capping. I review recent progress in Drosophila telomere studies, and challenge the notion that Drosophila may not be a relevant model for the study of telomere maintenance. This review article is part of a series dedicated to the eighth International conference on Drosophila heterochromatin, held in Gubbio (Italy), June 2007.     

Direct and potent regulation of gamma-secretase by its lipid microenvironment

gamma-Secretase is an unusual and ubiquitous aspartyl protease with an intramembrane catalytic site that cleaves many type-I integral membrane proteins, most notably APP and Notch. Several reports suggest that cleavage of APP to produce the Abeta peptide is regulated in part by lipids. As gamma-secretase is a multipass protein complex with 19 transmembrane domains, it is likely that the local lipid composition of the membrane can regulate gamma-activity. To determine the direct contribution of the lipid microenvironment to gamma-secretase activity, we purified the human protease from overexpressing mammalian cells, reconstituted it in vesicles of varying lipid composition, and examined the effects of individual phospholipids, sphingolipids, cholesterol, and complex lipid mixtures on substrate cleavage. A conventional gamma-activity assay was modified to include a detergent-removal step to facilitate proteoliposome formation, and this increased baseline activity over 2-fold. Proteoliposomes containing sphingolipids significantly increased gamma-secretase activity over a phosphatidylcholine-only baseline, whereas the addition of phosphatidylinositol significantly decreased activity. Addition of soluble cholesterol in the presence of phospholipids and sphingolipids robustly increased the cleavage of APP- and Notch-like substrates in a dose-dependent manner. Reconstitution of gamma-secretase in complex lipid mixtures revealed that a lipid raft-like composition supported the highest level of activity compared with other membrane compositions. Taken together, these results demonstrate that membrane lipid composition is a direct and potent modulator of gamma-secretase and that cholesterol, in particular, plays a major regulatory role.     

pH-dependent structures and properties of casein micelles

The association behavior of casein over a broad pH range has first been investigated by fluorescent technique together with DLS and turbidity measurements. Casein molecules can self-assemble into casein micelles in the pH ranges 2.0 to 3.0, and 5.5 to 12.0. The hydrophobic interaction, hydrogen bond and electrostatic action are the main interactions in the formation of casein micelles. The results show that the structure of casein micelles is more compact at low pH and looser at high pH. The casein micelle has the most compact structure at pH 5.5, when it has almost no electrostatic repulsion between casein molecules.     

Nanoscale porous silicon waveguide for label-free DNA sensing

Porous silicon (PSi) is an excellent material for biosensing due to its large surface area and its capability for molecular size selectivity. In this work, we report the experimental demonstration of a label-free nanoscale PSi resonant waveguide biosensor. The PSi waveguide consists of pores with an average diameter of 20nm. DNA is attached inside the pores using standard amino-silane and glutaraldehyde chemistry. Molecular binding in the PSi is detected optically based on a shift of the waveguide resonance angle. The magnitude of the resonance shift is directly related to the quantity of biomolecules attached to the pore walls. The PSi waveguide sensor can selectively discriminate between complementary and non-complementary DNA. The advantages of the PSi waveguide biosensor include strong field confinement and a sharp resonance feature, which allow for high sensitivity measurements with a low detection limit. Simulations indicate that the sensor has a detection limit of 50nM DNA concentration or equivalently, 5pg/mm2.