EAGER: Did Oxygenic Photosynthesis Cause Marine Group 1 Crenarchaeota to Take a Dive?

EAGER：产氧光合作用是否导致海洋第 1 类泉古菌潜水？

• 批准号: 0943278
• 负责人: James Hollibaugh
• 金额: $ 9.6万
• 依托单位: University of Georgia Research Foundation Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0943278&HistoricalAwards=false
• 关键词: EAGER; Did; Oxygenic; Photosynthesis; Cause

The presence of hydrogen peroxide in surface seawater is tied to solar radiation and its concentration varies seasonally as well as diurnally. H2O2 concentrations in the environment are low relative to those tolerated by many Bacteria, but relative to Bacteria, marine group 1 Crenarchaeota (MG1C) appear to lack defenses against it. Thus, photic zone concentrations of H2O2 may be sufficient to inhibit MG1C metabolism if they have not developed alternative strategies for mitigating H2O2 toxicity, for example by eliminating, replacing or protecting sensitive targets in the cell with structures that are less susceptible to H2O2 poisoning. Given that only 2 MG1C genomes have been sequenced and that these sequences have not been fully annotated, let alone had the annotations verified experimentally, it is difficult to infer from genomic evidence whether MG1C have other adaptations for dealing with H2O2 in the environment. Thus, this project will to address this question directly by testing MG1C sensitivity to H2O2 by combining toxicity bioassays of mesopelagic plankton assemblages with MicroAutoRadiography-Fluorescent In Situ Hybridization (MAR-FISH) to identify target groups. If the proposed experiments verify that MG1C are sensitive to H2O2, this property of MG1C could answer a number of questions. 1) The global and seasonal distributions of MG1C - why they do not live in the surface layer; their seasonal distribution at high latitudes; and their distributions relative to Euryarchaeota, which have more catalases and peroxidases and are more common in surface waters and nearshore environments. 2) Substrate utilization and metabolism patterns - if they are sensitive to it, MG1C can only use substrates or metabolize via pathways that do not generate H2O2. 3) Lack of Archaeal pathogens - a burst of reactive oxygen species (ROS) is an animal host's first line of defense against pathogens. 4) Why MG1C are hard to culture - many standard lab practices generate ROS; this may apply to Bacteria that have proven hard to culture as well, as not all Bacteria have catalase or peroxidase genes. 5) The divergence between Bacteria and Archaea - peroxide sensitivity may result from a "frozen metabolic accident" that was a fundamental property of Archaeal biochemistry at about the time that oxygenic photosynthesis evolved. 6) Some of the biochemical and compositional differences between Bacteria and Archaea - one way some Bacteria have adapted to high-ROS lifestyles has been to eliminate or protect ROS targets in their cellular machinery.This is a pilot project of limited scope and budget. Nonetheless it will contribute directly to graduate and undergraduate education. Results will be disseminated via publications and presentations at meetings and in the classroom, and data will be made publicly available in accordance with NSF's data release policy. Although the problem is important and that the arguments and evidence in favor of the hypothesis are provocative and convincing, they are circumstantial, speculative and would not pass the test of peer-review. The implications of the hypothesis are transformative, however, and this project would allow a limited test of this hypothesis.

表层海水中过氧化氢的存在与太阳辐射有关，其浓度随季节和昼夜变化。环境中的H2 O2浓度相对于许多细菌耐受的浓度较低，但相对于细菌，海洋组1 Crenarchaeota（MG 1C）似乎缺乏对其的防御。因此，如果他们没有开发出减轻H2 O2毒性的替代策略，例如通过消除，用不易受H2 O2中毒影响的结构替代或保护电池中的敏感目标。鉴于只有2个MG 1C基因组被测序，并且这些序列尚未被完全注释，更不用说实验验证注释了，因此很难从基因组证据中推断MG 1C是否具有处理环境中H2 O2的其他适应性。因此，本项目将直接解决这个问题，通过测试MG 1C的敏感性H2 O2相结合的毒性生物测定的中层浮游生物组合与微自动放射照相-荧光原位杂交（MAR-FISH），以确定目标群体。如果所提出的实验证实MG 1C对H2 O2敏感，那么MG 1C的这种性质可以回答许多问题。1)MG 1C的全球和季节性分布-为什么它们不生活在表层;它们在高纬度地区的季节性分布;以及它们相对于广古菌的分布，广古菌具有更多的过氧化氢酶和过氧化物酶，并且在表面沃茨和近岸环境中更常见。2)底物利用和代谢模式-如果它们对其敏感，MG 1C只能使用底物或通过不产生H2 O2的途径代谢。3)缺乏肠道病原体-活性氧（ROS）的爆发是动物宿主对抗病原体的第一道防线。4)为什么MG 1C很难培养-许多标准的实验室实践产生ROS;这可能也适用于已被证明很难培养的细菌，因为并非所有细菌都有过氧化氢酶或过氧化物酶基因。5)细菌和细菌对过氧化物敏感性的差异可能是由于“冷冻代谢事故”造成的，这是大约在产氧光合作用进化的时候，细菌生物化学的一个基本特性。6)细菌和细菌之间的一些生化和成分差异-一些细菌适应高活性氧生活方式的一种方式是消除或保护其细胞机器中的活性氧目标。这是一个范围和预算有限的试点项目。尽管如此，它将直接促进研究生和本科生教育。研究结果将通过出版物和在会议和课堂上的演讲进行传播，数据将根据NSF的数据发布政策公开提供。虽然这个问题很重要，而且支持这个假设的论点和证据是挑衅性的和令人信服的，但它们是间接的、推测性的，不会通过同行评审的考验。然而，这一假设的影响是变革性的，这个项目将允许对这一假设进行有限的检验。