LEXEN: Microbial Adaptation to High Temperature and Pressure

超高温微生物可能是祖先生物系统的合适模型，也可能是外星生物系统的模型，因为它们非凡的适应能力使它们能够在地球上广泛的地下火山区定居。深海热液喷口和陆地温泉在没有太阳能的情况下支持高度多样化的生态系统，在类似于火星或欧罗巴表面下可能存在的地球化学条件下，庇护着自养微生物及其依附的异养微型和宏观群落。嗜热菌还支配着通用系统发育树的大多数更深层次的分支，这表明祖先的微生物可能是嗜热菌。利用生物工程、微生物学和分子生物学的组合，将建立已知的超高温物种以及新分离的菌株的生长和生存的环境限制。这项与加州大学伯克利分校道格拉斯·S·克拉克博士(9816490)的合作项目强调了分子对高压和高温的适应，目标如下：1.确定超最佳温度和压力对现有超高温微生物生存和生长速度的影响；2.利用加压连续发酵系统分离和培养新的超高温微生物菌株；3.检测对高温和高压瞬变挑战的生理适应和基因表达的遗传调节。正在测试的假设是，静水压力可能会极大地延长超嗜热菌生长和存活的上限温度。这些研究人员正在进行的研究已经证实，来自嗜热菌的许多酶在压力下表现出更高的热稳定性。此外，随着压力的增加，詹纳斯基甲烷球菌的生长速度加快了5倍，其产甲烷的最高温度上升了6摄氏度，而一种新表征的深海嗜热菌--horikoshii的生长速度和ATP产量在压力下得到了提高。用于在连续培养、加压和热循环中培养高温细菌的新型设备将与分子生物学相结合，以探索高温细菌在极端情况下的适应反应。将对基因表达、膜脂成分和形态进行检测。在接近致命性的条件下诱导的基因将通过消减克隆和转录分析来鉴定。利用来自浅层陆地采样点的分离物为压力反应提供控制数据，将确定深海嗜热细菌的生存上限作为压力的函数。来自西北太平洋弧后地区(冲绳海槽和堪察加半岛上的Uzzon Caldera)喷口系统的超嗜热菌的浓缩培养将在超过已知菌株所能耐受的温度和压力下培养，从而使用存活而不是快速生长作为选择新菌株的标准。新菌株的系统发育位置和生理需求将被确定。

Hyperthermophilic microorganisms may be suitible models for ancestral, and possibly extraterrestrial, biosystems because their extraordinary adaptive capabilities allow them to colonize a wide range of subsurface volcanic areas on Earth. Deep sea hydrothermal vents and terrestrial hot springs support highly diverse ecosystems without access to solar energy, harboring autotrophic microorganisms and their dependant heterotrophic micro- and macro communities in geochemical conditions similar to those that may exist below the surface of Mars or Europa. Hyperthermophiles also dominate most of the deeper branches of the universal phylogenetic tree, suggesting that ancestral microorganisms may have been thermophilic. The environmental limits for growth and survival of known hyperthermophilic species, as well as newly isolated strains will be established, using a combination of bioengineering, microbiology and molecular biology. This collaborative project with Dr. Douglas S. Clark of the University of California, Berkeley (Award 9816490) emphasizes molecular adaptations to high pressure and high temperature, with the following objectives: 1. To determine the effects of supraoptimal temperatures and pressures on the survival and growth rates of existing hyperthermophilic microorganisms;2.To utilize pressurized continuous fermentation systems for isolation and culture of new hyperthermophilic microbial strains and; 3. To examine physiological adaptations and genetic regulation of gene expression in response to transient challenges by heat and high pressure. The hypothesis being tested is that hydrostatic pressure may greatly extend the upper temperature limits of growth and survival of hyperthermophiles. Ongoing studies by these researchers have established that many enzymes from thermophiles display enhanced thermostability under pressure. Further, the growth rate of Methanococcus jannaschii accelerated five-fold and its maximum temperature for methane production rose by 6 degrees C in response to pressure, and the growth rate and ATP production of a newly characterized abyssal hyperthermophile, Pyrococcus horikoshii, were elevated under pressure. Novel equipment for incubating hyperthermophiles in continuous culture, under pressure and with thermal cycling, will be combined with molecular biology to explore the adaptive responses of hyperthermophiles in extremis. Gene expression, membrane lipid composition and morphology will be examined. The genes that are induced under conditions approaching lethality, will be identified by subtractive cloning and transcriptional assays. Upper survival limits of the abyssal hyperthermophiles as a function of pressure, using isolates from a shallow terrestrial sampling site to provide control data for pressure responses, will be determined. Enrichment cultures of hyperthermophiles from the vent systems of the back-arc region of the Northwest Pacific (Okinawa Trough and Uzzon Caldera on the Kamchatka Peninsula) will be incubated at temperatures and pressures exceeding those tolerated by known strains, thus using survival rather than rapid growth as the criterion for selection of new isolates. The phylogenetic positions and physiological requirements of the new strains will be determined.