Fine structure of the mesosome and nucleoid in frozen-etchedBacillus subtilis

Summary An electron microscopical investigation ofBacillus subtilis prepared by freeze-etching revealed the fine structural changes that occur in the cell prior to spore formation. The initiation of growth from lyophilized cells was characterized by the appearance of numerous vesicular structures embedded in and attached to the plasma membrane. As growth continued, the number of vesicular structures decreased and lamellar membrane structures began to appear. Prior to spore formation, a fine, fibrillar material was found in the central portion of the cell and was believed to be the DNA.     

损伤条件下油菜黄单胞菜豆致病变种内源过氧化氢与间体形成的联系

【目的】本实验通过透射电子显微镜观察黄单胞菌在细胞损伤条件下的亚细胞结构和过氧化氢积累定位的变化。【方法】采用氯化铈对过氧化氢特异染色的组织化学法。【结果】细菌细胞受损伤后,出现了一个细胞壁之外的过氧化氢大量积累的额外位点。并且这个额外位点出现的频率和过氧化氢积累量都与细胞损伤的程度密切相关。另一方面,亚细胞结构的常规染色结果也显示,受到损伤的细胞中也出现一个额外的亚显微结构,即间体。间体出现的频率和大小也随着细胞损伤程度的增加而显著上升。【结论】多元线性回归分析的结果证明细胞损伤条件下细菌中出现的额外过氧化氢大量积累的位点就是间体。细胞损伤后间体中的过氧化氢积累对受损细胞应是一种主动调控机制。     

Relationship between the DNA content and mesosome number in cells of Bacillus.

In cells of Bacillus there is evidence that deoxyribonucleic acid forms an association with some membranous structure within the cell, possibly mesosomes. Cells of varieties of Bacillus cereus and Bacillus subtilis were examined to see if any quantitative relationship existed between the numbers of mesosomes and DNA content. No direct relationship could be domonstrated. However, cells of Bacillus cereus var. alesti A(-) maintained a characteristic and constant DNA content and number of mesosomes regardless of growth conditions. During sporulation, a variant of A(-), termed A(-)3, SEQUESTERS ITS DNA at both ends of the cell, leaving a small amount of DNA but no mesosomes in the center compartment. Since this center compartment is capableof growth and division upon replacement in fresh medium (rejuventation) it was examinedfor mesosome content as DNA synthesis and division were initiated. In most cells, acentral mesosome was formed at the site of cell septum formation; however, the presenceof a mesosome was not an absolute prerequisite for cell division. We propose that atthe onset of cell growth, mesosomes primarily function in the process of cell septum formation. As growth and division proceed, mesosomes are produced in characteristicnumbers and may act as the site of DNA synthesis and (or) segregation.     

The bacterial cytoskeleton

Bacteria contain a complex cytoskeleton that is more diverse than previously thought. Recent research provides insight into how bacterial actins, tubulins, and ParA proteins participate in a variety of cellular processes.     

The bacterial chromosome

Bacteria represent the vast majority of biological diversity found on Earth. In this review, we focus on selected aspects of their genetic material, those providing insight into structural, functional, dynamic, and evolutionary aspects of their genomes. Bacterial chromosomes are far more dynamic than previously realized, and dozens of mechanisms giving rise to genomic plasticity are now understood. Maturation of the genomics era has provided the tools for unraveling the interwoven details of DNA structure/function relationships that provide a basis for organismal diversity. Some of the most throughly understood processes that underlie the dynamics of genomic structure and function in prokaryotes are examined.     

The bacterial lipocalins

The lipocalins were once regarded as a eukaryotic protein family, but new members have been recently discovered in bacteria. The first bacterial lipocalin (Blc) was identified in Escherichia coli as an outer membrane lipoprotein expressed under conditions of environmental stress. Blc is distinguished from most lipocalins by the absence of intramolecular disulfide bonds, but the presence of a membrane anchor is shared with two of its closest homologues, apolipoprotein D and lazarillo. Several common features of the membrane-anchored lipocalins suggest that each may play an important role in membrane biogenesis and repair. Additionally, Blc proteins are implicated in the dissemination of antibiotic resistance genes and in the activation of immunity. Recent genome sequencing efforts reveal the existence of at least 20 bacterial lipocalins. The lipocalins appear to have originated in Gram-negative bacteria and were probably transferred horizontally to eukaryotes from the endosymbiotic alpha-proteobacterial ancestor of the mitochondrion. The genome sequences also reveal that some bacterial lipocalins exhibit disulfide bonds and alternative modes of subcellular localization, which include targeting to the periplasmic space, the cytoplasmic membrane, and the cytosol. The relationships between bacterial lipocalin structure and function further illuminate the common biochemistry of bacterial and eukaryotic cells.     

The bacterial flagellar motor

The bacterial flagellar motor is a remarkable molecular machine that converts chemical energy into work. Knowledge of the structure, genetics, and dynamics of the motor has expanded steadily. Recent progress is reviewed, with an emphasis on the dynamics of flagellar rotation. Previous results with tethered cells, which rotate slowly, are contrasted with recent work on swimming cells, whose motors turn very rapidly. Genetic evidence delineates a small set of proteins that are likely to participate directly in the process of torque generation. An explicit hypothesis for torque generation is described, in which roles are envisaged for each of these proteins.     

The bacterial cytoskeleton.

In recent years it has been shown that bacteria contain a number of cytoskeletal structures. The bacterial cytoplasmic elements include homologs of the three major types of eukaryotic cytoskeletal proteins (actin, tubulin, and intermediate filament proteins) and a fourth group, the MinD-ParA group, that appears to be unique to bacteria. The cytoskeletal structures play important roles in cell division, cell polarity, cell shape regulation, plasmid partition, and other functions. The proteins self-assemble into filamentous structures in vitro and form intracellular ordered structures in vivo. In addition, there are a number of filamentous bacterial elements that may turn out to be cytoskeletal in nature. This review attempts to summarize and integrate the in vivo and in vitro aspects of these systems and to evaluate the probable future directions of this active research field.     

细菌性阴道病的细菌因素研究进展

细菌性阴道病是妇科常见疾病,对女性、胎儿和新生儿的健康构成严重威胁.阴道微生物群落中产H2O2的乳酸杆菌与厌氧菌数量发生转换为其主要特征,具体机制不清.本文系统综述了近年来细菌性阴道病的细菌因素研究进展.     

The bacterial ParA-ParB partitioning proteins

A pair of genes designated parA and parB are encoded by many low copy number plasmids and bacterial chromosomes. They work with one or more cis-acting sites termed centromere-like sequences to ensure better than random predivisional partitioning of the DNA molecule that encodes them. The centromere-like sequences nucleate binding of ParB and titrate sufficient protein to create foci, which are easily visible by immuno-fluorescence microscopy. These foci normally follow the plasmid or the chromosomal replication oriC complexes. ParA is a membrane-associated ATPase that is essential for this symmetric movement of the ParB foci. In Bacillus subtilis ParA oscillates from end to end of the cell as does MinD of E. coli, a relative of the ParA family. ParA may facilitate ParB movement along the inner surface of the cytoplasmic membrane to encounter and become tethered to the next replication zone. The ATP-bound form of ParA appears to adopt the conformation needed to drive partition. Hydrolysis to create ParA-ADP or free ParA appears to favour a form that is not located at the pole and binds to DNA rather than the partition complex. Definition of the protein domains needed for interaction with membranes and the conformational changes that occur on interaction with ATP/ADP will provide insights into the partitioning mechanism and possible targets for inhibitors of partitioning.