種別 ワークショップ 提案者 水之江義充（九大・院医・細菌）
小林一三 （東大・医科研）趣旨 細胞の死は、細胞の分化・生物の進化にとって非常に重要な役割を果たして来たと考えられる。分化・進化の起源を細菌のプログラム死に焦点をあて討議する。 予定講演者の氏名、所属、タイトル
- 「細菌の飢餓状態における生存戦略（VNC:viable but nonculturableへの移行およびバイオフィルム形成）」
水之江義充（九大・院医・細菌）
Vibrio cholerae, a gram-negative, motile aquatic bacterium, is the causal agent of the diarrheal disease, cholera. Cholera is a serious epidemic disease that has killed millions of people and continues to be a major health problem world-wide. The hypothesis that V. cholerae occupies an ecological niche in the estuarine environment required that this organism be able to survive the dynamics of physiochemical stresses, including nutrient starvation. As a result of these stresses, bacteria in nature often exist in nongrowth or very slow growth states with low metabolic activity. The organisms only have a limited capacity to control their environment and they almost invariably respond to environmental changes by changing themselves. In principle, this can occur in two ways, namely, by changes in their genetic constitution or by phenotypic adaptation. How organisms survive during environmental stress is a fundamental question of biology. In this report, we will focus on the phenotypic responses of V. cholerae to starvation-stress; entry into viable but nonculturable state and biofilm formation.- 「枯草菌の胞子形成と母細胞の死」
佐藤 勉（東京農工大・農学研究科）
The unicellular bacterium Bacillus subtilis offers a particularly well-suited model system to study biological mechanisms of cellular differentiation because of its ability to differentiate to form a heat-resistant endospore in the mother cell in response to nutrient depletion and because its entire genome has been sequenced. During sporulation, an ordered sequence of morphological events takes place starting with the formation of an asymmetrically positioned septum that divides the sporangium into two unequal compartments: the forespore and the mother cell. Each compartment contains a chromosome and engages in a sporulation specific program governed by four different, sporulation-specific sigma factors, whose activities are tightly regulated both temporally and spatially. We are focusing on the programmed death of the mother cell, which is actively lysed prior to release of the spore. The obvious function of mother cell lysis is to eliminate a barrier that could interfere with outgrowth of a germinating spore. We have analyzed this process and found the following order of events: 1) spore detachment from the polar site of the mother cell, 2) membrane breakage 3) DNA degradation, 4) cell-wall collapse and 5) release of the free spore. We will discuss the regulation of mother cell death.- 「海洋での細菌の死滅プロセス」
木暮一啓（東大・海洋研）
The goal of marine microbiology is to clarify ecological roles of each bacterial species in the ocean. This requires methods to detect single cell at minute scale of space and time. However, our current methods do not have enough precision for this purpose. In addition, there is no suitable method to estimate the death rate of natural populations. Therefore, we usually assume that bacterial growth is balanced with the death. As a result, there is no any extensive study of the distribution, growth and death of particular bacterial species.We recently clarified that Pseudomonas aeruginosa is distributed in Tokyo Bay and also that their outer membrane channel protein, porin is present in the seawater as dissolved components. The PFGE analysis indicates that the cells in the bay are different from clinical isolates and are lacking resistance to various antibiotics, suggesting the presence of a population unique to marine environments. We assume that most of cells of P. aeruginosa originated from freshwater or terrestrial environments may die upon entering the bay, due to viral infection or ingestion by heterotrophic nanoflagellates. The fate of P. aeruginosa in the bay will be discussed based on some quantitative approach.
- 「バクテリアの細胞死に関与する蛋白質複合体構造」
鎌田勝彦(理研）
Some plasmids possess a genetic system known as addiction modules that govern programmed cell death. This control mechanism consists of pairs of genes that encode two protein components: a stable toxin and an unstable antidote. Daughter cells lacking the plasmid are killed by stable toxin proteins once the unstable antidote is degraded, whereas those inheriting the plasmid survive. Similar system also operates at the level of bacterial chromosomes (MazE/MazF and ChpBI/ChpBK antidote/toxin pairs in E. coli). Genes encoding these protein pairs appear to have coevolved to give rise to analogous cell killing systems in various biological contexts. A structure of the Escherichia coli chromosomal MazE/MazF addiction module has been determined at 1.7 A resolution. MazE (antidote) and MazF (toxin) form a linear heterohexamer composed of alternating homodimers (MazF2-MazE2-MazF2). The MazE homodimer forms a novel barrel domain from which two extended C termini project, making interactions with flanking MazF homodimers that resemble the plasmid-encoded toxins CcdB and Kid. The MazE/MazF heterohexamer structure documents that the mechanism of antidote-toxin recognition is common to both chromosomal and plasmid borne addiction modules, and provides general molecular insights into toxin function, antidote degradation in the absence of toxin, and promoter DNA binding by antidote/toxin complexes.- 「大腸菌の分化と死：自然界での生存機構を知るための試み」
石浜 明（日本生物科学研）
During transition of E. coli growth from exponential to stationary phase, marked changes take place in the cell shape, cell surface structure, nucleoid conformation, cytosol composition, and gene expression pattern. A number of the stationary-phase genes are involved in these processes. The growth phase-coupled alteration in gene expression pattern depends on the changes in activity and specificity of both transcription and translation apparatus. For determination of the order of differentiation-associated molecular events, use of homogenous cell populations with respect to the cell differentiation is absolutely required. After extensive trials, we succeeded to fractionated random E. coli cultures into homogenous cell populations by using Percoll gradient centrifugation. The success was based on the discontinuous increase in cell buoyant density with the advance in cell age. After search for E. coli mutants defective in the increase of cell density, we found that a specific set of the genes are involved in each step of the cell differentiation. We propose the order of expression of the genes for E. coli differentiation.