Marine Biotechnology Fellowship: Role of Chromosome- Associated DNA Binding Proteins in the Viable but Nonculturable State of Vibrio Vulnificus

在海水中，大约有50%的活性细菌会抵抗培养的尝试。其中一个原因可能是，在自然的压力条件下，细菌能够进入一种有活力但不生长的状态。活但不可培养（VBNC）状态涉及一种代谢程序，在这种状态下细胞保持活力并保持低水平的代谢，但不能培养。了解控制进入这种状态的因素可能为进入海洋中不可培养细菌的生物学提供了一个窗口。研究进入和退出VBNC状态的最佳表征系统是海洋细菌创伤弧菌。V. vulnificus在温度下降时进入VBNC状态。进入VBNC状态会在DNA水平上产生问题：染色体相关的DNA结合蛋白（有时称为“组蛋白样”蛋白）可能在VBNC状态中起重要作用。其中一种蛋白质HNS已被证明在体内沉默转录，并在体外稳定和有序DNA结构。它的多效性表明，这种蛋白质在允许细胞感知各种类型的环境变化中起作用。HNS是一种丰富的冷诱导蛋白，其浓度在细胞生长周期中发生变化，在静止期（相对代谢静止期）达到最大浓度。该项目将验证这样一个假设，即在温度降低的过程中，创伤弧菌的HNS同源物被诱导，沉默正常生长所需基因的表达，并导致该细菌的VBNC状态。这样一个系统可以解释海洋环境中不可培养细菌的很大一部分。＊＊＊

McGovern 9321699 Approximately 50% of the active bacteria that can be counted in seawater resist attempts to culture. One reason may be that bacteria are capable, under natural conditions of stress, of entering a viable but nongrowing state. The viable but nonculturable (VBNC) state involves a metabolic program in which the cell remains viable and maintains a low level of metabolism, but cannot be cultured. Understanding the factors that govern entry into this state may provide a window of entry into the biology of the uncluturable bacteria of the ocean, The best characterized system for studying entry into and exit form the VBNC state is the marine bacterium Vibrio vulnificus. V. vulnificus enters the VBNC state in response to temperature downshifts. Entry into the VBNC state poses problems at the DNA level: the chromosome-associated DNA binding proteins (sometimes called "histone-like" proteins) may play an important role in the VBNC state. One of the these proteins, HNS, has been shown to silence transcription in vivo and to stabilize and ordered DNA structure in vitro. Its pleiotropic effects indicate that this protein plays a role in allowing cells to sense various types of environmental change. HNS is an abundant, cold-inducible protein that varies in concentration over the course of a cell's growth cycle, reaching its maximal concentration during stationary phase, a period of relative metabolic quiescence. This project will test the hypothesis that during a temperature downshift, the V. vulnificus homolog of HNS is induced, silencing expression of genes needed for normal growth and leading to the VBNC state in that bacterium. Such a system could account for a significant portion of the nonculturable bacteria present in the ocean environment. ***