Bacterial nucleoid dynamics: oxidative stress response in Staphylococcus aureus

A single-molecule-imaging technique, atomic force microscopy (AFM) was applied to the analyses of the genome architecture of Staphylococcus aureus. The staphylococcal cells on a cover glass were subjected to a mild lysis procedure that had maintained the fundamental structural units in Escherichia coli. The nucleoids were found to consist of fibrous structures with diameters of 80 and 40 nm. This feature was shared with the E. coli nucleoid. However, whereas the E. coli nucleoid dynamically changed its structure to a highly compacted one towards the stationary phase, the S. aureus nucleoid never underwent such a tight compaction under a normal growth condition. Bioinformatic analysis suggested that this was attributable to the lack of IHF that regulate the expression of a nucleoid protein, Dps, required for nucleoid compaction in E. coli. On the other hand, under oxidative conditions, MrgA (a staphylococcal Dps homolog) was over-expressed and a drastic compaction of the nucleoid was detected. A knock-out mutant of the gene encoding the transcription factor (perR) constitutively expressed mrgA, and its nucleoid was compacted without the oxidative stresses. The regulatory mechanisms of Dps/MrgA expression and their biological significance were postulated in relation to the nucleoid compaction

ダイチョウキン センショクタイ ノ コウゾウ コウチク ニ カンスル ケンキュウ

京都大学0048新制・課程博士博士(生命科学)甲第13239号生博第109号新制||生||16(附属図書館)UT51-2007-H512京都大学大学院生命科学研究科統合生命科学専攻(主査)教授 竹安 邦夫, 教授 井上 丹, 教授 下遠野 邦忠学位規則第4条第1項該当Doctor of Life ScienceKyoto UniversityDA

Longitudinal Change in Brain Functional Connectivity with Herpes Zoster Patients: Neuroimaging Case Series

The exact mechanism involved in the development of postherpetic neuralgia (PHN) is not yet known. The objective of this study was to evaluate longitudinal functional connectivity (FC) changes in the neuroimaging case series of patients with acute herpes zoster (HZ). Cases: This study included five patients who had symptoms of HZ. Functional magnetic resonance imaging was conducted at enrollment and 3 months to determine FC changes. Of the five patients, three developed PHN. In the PHN subjects, the FC of the left superior frontal gyrus (SFG) and the right inferior frontal gyrus (IFG) were activated. The left SFG is known to contribute to higher cognitive functions and working memory. The right IFG is associated with pain processing and empathy for pain. Conclusions: Although only a few patients were enrolled in this study, the PHN could be affected by pain itself, as well as pain memory and psychological aspects such as empathy for pain

Fundamental structural units of the Escherichia coli nucleoid revealed by atomic force microscopy

A small container of several to a few hundred µm(3) (i.e. bacterial cells and eukaryotic nuclei) contains extremely long genomic DNA (i.e. mm and m long, respectively) in a highly organized fashion. To understand how such genomic architecture could be achieved, Escherichia coli nucleoids were subjected to structural analyses under atomic force microscopy, and found to change their structure dynamically during cell growth, i.e. the nucleoid structure in the stationary phase was more tightly compacted than in the log phase. However, in both log and stationary phases, a fundamental fibrous structure with a diameter of ∼80 nm was found. In addition to this ‘80 nm fiber’, a thinner ‘40 nm fiber’ and a higher order ‘loop’ structure were identified in the log phase nucleoid. In the later growth phases, the nucleoid turned into a ‘coral reef structure’ that also possessed the 80 nm fiber units, and, finally, into a ‘tightly compacted nucleoid’ that was stable in a mild lysis buffer. Mutant analysis demonstrated that these tight compactions of the nucleoid required a protein, Dps. From these results and previously available information, we propose a structural model of the E.coli nucleoid

Dynamic state of DNA topology is essential for genome condensation in bacteria

In bacteria, Dps is one of the critical proteins to build up a condensed nucleoid in response to the environmental stresses. In this study, we found that the expression of Dps and the nucleoid condensation was not simply correlated in Escherichia coli, and that Fis, which is an E. coli (gamma-Proteobacteria)-specific nucleoid protein, interfered with the Dps-dependent nucleoid condensation. Atomic force microscopy and Northern blot analyses indicated that the inhibitory effect of Fis was due to the repression of the expression of Topoismerase I (Topo I) and DNA gyrase. In the Δfis strain, both topA and gyrA/B genes were found to be upregulated. Overexpression of Topo I and DNA gyrase enhanced the nulceoid condensation in the presence of Dps. DNA-topology assays using the cell extract showed that the extracts from the Δfis and Topo I-/DNA gyrase-overexpressing strains, but not the wild-type extract, shifted the population toward relaxed forms. These results indicate that the topology of DNA is dynamically transmutable and that the topology control is important for Dps-induced nucleoid condensation