黄色粘球菌发育阶段外膜蛋白表达的变化

【目的】黄色粘球菌是研究原核发育的一种模式生物,对其膜蛋白的研究仍然十分缺乏。【方法】利用6种预测软件,在黄色粘球菌的基因组中筛选编码外膜蛋白(OMP)的基因。根据报告基因lacZ,检测这些基因在营养性生长和发育阶段的表达。【结果】基于生物信息学分析,筛选出11个编码外膜蛋白的基因。其中2个基因(MXAN3106和MXAN3883)在发育阶段表达量上升,它们分别编码Secretin家族和Fimbrial usher protein (FUP)家族转运蛋白。其余9个基因在发育起始阶段表达量降低或保持较低水平,它们均编码TonB依赖型受体或外排蛋白。【结论】这些数据提示,黄色粘球菌由生长到发育的转换过程,伴随着膜蛋白表达的显著变化。     

粪肠球菌生物被膜形成早期相关基因的表达研究

目的:以粪肠球菌为研究对象,探讨粪肠球菌基因srtA(转肽酶A编码基因)、esp(肠球菌表面蛋白)与粪肠球菌生物被膜形成早期的相关性。方法:用逆转录PCR与实时荧光定量PCR方法对生物被膜和浮游菌组细菌srtA、esp两种与生物被膜形成早期相关的基因其表达进行检测,并进行统计学分析。结果:srtA、esp基因与粪肠球生物被膜菌早期形成密切相关。生物被膜菌组srtA、esp表达量分别是浮游菌组的7.9与13.5倍。结论:srtA、esp基因与粪肠球生物被膜菌形成早期密切相关,可能是生物被膜早期形成的上调因子。     

细菌生物被膜的耐药机制及控制策略

在特定的条件下,细菌可以形成生物被膜,包被有生物被膜的细菌称为被膜菌.被膜菌无论其形态结构、生理生化特性、致病性还是对环境因子的敏感性等都与浮游细菌有显著的不同,尤其对抗生素和宿主免疫系统具有很强的抵抗力,从而导致严重的临床问题,引起许多慢性和难治性感染疾病的反复发作.细菌生物被膜粘附在各种医疗器械及导管上极难清除,以至引发大量的医源性感染.近年来,随着人们对细菌致病机制认识的逐步深入,控制细菌生物被膜的方法已有较大发展.本文拟探讨被膜菌的耐药机制并着重综述细菌生物被膜控制方法的最新研究进展.     

细菌生物被膜与食品生物危害

食源性病原菌生物被膜是威胁食品安全的一个重大隐患。生物被膜一旦在食品加工过程中形成,易引起相当严重的交叉污染和加工后污染,产生极大危害,从而导致一系列严重的健康问题。本文就食源性病原菌生物被膜的分布、形成机制以及防治措施进行了综述。     

生物被膜分散方式的研究进展

临床上生物被膜与感染的慢性迁延不愈密切相关,而生物被膜菌的分散又会造成感染的反复急性发作,给临床感染的有效控制带来很大困难。生物被膜菌的分散过程受到了遗传和环境等多因素的调控,主要是通过蜂式分散、块式分散和毯式分散3种形式来实现的。深入进行生物被膜基础研究对改变目前临床感染治疗的窘境有重大意义。     

细菌生物被膜检测方法的研究进展

细菌生物被膜(bacterial biofilm,BF)是细菌黏附于接触物表面,由细菌自身分泌的胞外基质包裹形成的多细胞微生物群体,是微生物界细菌普遍的生存状态。基于生物被膜的物理屏障作用和膜内特殊微环境,其具有多重耐药性以及较强的黏附性、抗吞噬性等特性,导致所致疾病迁延不愈,已成为医疗卫生领域的重大挑战。早期、快速、准确检测生物被膜形成对及时有效防治其感染性疾病至关重要。现从表型和基因型检测两个方面对细菌生物被膜检测方法作一综述。     

白色念珠菌生物被膜研究进展

难治性真菌感染的临床分析发现,病灶感染病原常以生物被膜的形态存在。生物被膜的形成可帮助真菌躲避宿主细胞免疫系统清除和药物的攻击,所造成的持续性感染严重威胁人类健康,因此,认识研究真菌生物被膜及其耐药机理对于防治临床真菌感染有着重大意义。白色念珠菌是一种临床感染常见的条件性致病菌,也是目前真菌生物被膜研究的主要研究模型。白色念珠菌生物被膜主要由多糖、蛋白质和DNA构成,其形成由微生物间的群体感应调控,并受到环境中营养成分及其附着物表面性质影响。研究发现,胞外基质的屏障作用、耐药基因的表达等机制与生物被膜耐药性的产生密切相关。本文就白色念珠菌生物被膜的形成过程、结构组成、形成的影响因素、现有研究模型、耐药机制和治疗策略等几个方面介绍近年来的研究进展。     

根除细菌生物被膜的新视角：分散

细菌生物被膜(biofilm,BF)是细菌为对抗外界压力形成的一种自我保护结构,对于抗菌药物具有极高的耐受性,在临床上极易引发难治性慢性感染。BF分散是指在BF形成周期中,膜内细胞主动逸出,恢复浮游生长模式,寻找新定植位点的过程。由于细菌在浮游状态下,更易受到抗菌药与免疫反应的作用,诱导BF分散是控制BF相关感染(biofilm-associated infections, BAI)的一条富有前景的策略。本文从BF分散的方式和信号分子等角度,对BF分散的调控机制进行分析;归纳能影响BF分散的物质,并对BF分散后可能带来的危害及未来的研究思路进行简述,以期为研发新型分散剂和深入研究药物作用的靶点提供理论参考。     

生物被膜的物理特性及其表征

生物被膜涉及到人类生产生活的方方面面。生物被膜的形成有时是有益的,可用于生物降解、生物催化等;但同时也造成了诸多不利的影响,医疗领域中的感染性疾病、工业生产中的生物污损等均与生物被膜的形成有关。生物被膜形成过程中的物理性质决定着生物被膜的形态结构以及机械稳定性,对它在应对外界环境刺激并得以生存具有重要的意义。本文介绍了生物被膜形成初期和发展过程中的物理性质以及相应的表征手段。其中,细菌的表面粘附由细菌的近界面运动行为及细菌与表面的相互作用决定,并对生物被膜的初期形成起关键的作用。此外,机械性能测试发现成熟的生物被膜可看作具备粘弹性的聚合物。     

The extracellular proteases of Myxococcus xanthus

Abstract A zymogram technique was used to resolve the proteases from the culture supernatants of three strains derived from Myxococcus xanthus FB. Of the 8 bands obtained, 3 were possibly proteolytic artefacts, and another may be derived from membrane vesicles or fragments. 3 of the bands were tentatively identified as serine proteases by affinity labelling. A non-motile, non-fruiting strain, M. xanthus DZ1, differed from 2 wild-type strains, NCIB9412 and DK101, in the relative intensity of certain bands, and all 3 strains differed qualitatively from M. xanthus XK, which is not FB-derived.     

Effects of pH and phosphate on the production of struvite by Myxococcus xanthus

We studied the influence of pH and the phosphate content of the culture medium on the precipitation of struvite by Myxococcus xanthus, a bacterium that undergoes autolysis at the end of its exponential growth phase in liquid cultures. The best results were obtained with pH values between 7.2 and 8.0 and with a phosphate concentration of 10 mM. Our studies reveal for the first time that the precipitation of struvite always begins at the onset of autolysis and that culture conditions favoring the early occurrence of autolysis also enhance struvite production.     

Transposon Tn5 confers streptomycin resistance to Myxococcus xanthus

Abstract In addition to resistance to kanamycin, transposon Tn 5 confers resistance to streptomycin in Myxococcus xanthus . The streptomycin determinant is located within the Bgl II fragment of Tn 5 . The level of resistance varies among strains bearing Tn 5 insertions in different chromosomal loci and there is a correlation between the levels of resistance to streptomycin and to kanamycin.     

Increases in the intracellular concentration of glycerol during development in Myxococcus xanthus S. Courtney Frasch

Abstract The role of glycerol as a natural morphogen of myxospore formation in Myxococcus xanthus was examined. Glycerol was extracted from cells undergoing development and analyzed by gas chromatography. Glycerol is present in cells, and the intracellular level undergoes a series of transient increases during development. The data suggest a role for glycerol in myxosporulation and fruiting body morphogenesis supporting the notion that this chemical induction of sporulation may represent a physiological pathway in development.     

Transcriptional regulation of genes required for antibiotic TA synthesis in Myxococcus xanthus

Abstract Regulatory mutants were isolated for six genes required for the production of antibiotic TA in Myxococcus xanthus , using Tn5lac as a promoter probe. Two of the regulatory mutants were closely linked to their corresponding Tn5lac insertions and three were separated by at least 40 kb from their original insertions. All of the β-galactosidase-overproducing mutants showed higher specific activities than their parent strains in three different media. The specific activity was higher throughout the growth cycle, starting earlier and finishing higher. In addition to helping to understand the mechanism of repression of TA genes, the mutants are potentially useful in the construction of antibiotic-overproducing strains.     

Natural variation of gliding motility in a centimetre-scale population of Myxococcus xanthus

A major challenge in microbial evolutionary ecology is to understand how fitness-related traits vary in natural populations of microorganisms at defined spatial scales and subsequently to identify the forces that maintain such variation. The Gram-negative soil bacterium Myxococcus xanthus is a model system for the study of gliding motility, which is driven by two complementary motility systems in this species and is central to its social lifestyle. We tested whether the ecological context of a centimetre-scale M. xanthus population allows the coexistence of diverse motility-related phenotypes. Swarming rates among 26 clones isolated at the centimetre scale were found to vary greatly in multiple laboratory environments. This variation appears to be motility-specific, as it is not explained by a correlated variation in intrinsic growth rate. In contrast to the common reference strain DK1622, most isolates swarmed faster on hard agar than on soft agar, highlighting the difficulty of inferring species characteristics from laboratory reference strains. These isolates also varied greatly in swarm morphology and in the effect of nutrient limitation on swarming rate. Our results show that diverse swarming phenotypes can coexist in a small-scale bacterial population.     

Propionyl-CoA carboxylase of Myxococcus xanthus: catalytic properties and function in developing cells

An acyl-coenzyme A carboxylase that carboxylates acetyl-CoA, butyryl-CoA, propionyl-CoA, and succinyl-CoA was purified from Myxococcus xanthus. Since the enzyme showed maximal rates of carboxylation with propionyl-CoA, the enzyme is thought to be propionyl-CoA carboxylase. The apparent K _m values for acetyl-CoA, butyryl-CoA, propionyl-CoA, and succinyl-CoA were found to be 0.2, 0.2, 0.03, and 1.0 mM, respectively. The native enzyme has a molecular mass of 605–615 kDa and is composed of nonidentical subunits (α and β) with molecular masses of 53 and 56 kDa, respectively. The enzyme showed maximal activity at pH 7.0–7.5 and at 25–30°C, and was affected by variation in concentrations of ATP and Mg²⁺. During development of M. xanthus, the propionyl-CoA carboxylase activity increased gradually, with maximum activity observed during the sporulation stage. Previous work has shown that a propionyl-CoA-carboxylase-deficient mutant of M. xanthus reduces levels of long-chain fatty acids. These results suggest that the propionyl-CoA carboxylase is also responsible for the carboxylation of acetyl-CoA to malonyl-CoA used for the synthesis of long-chain fatty acids during development. Received: 24 February 1998 / Accepted: 25 May 1998