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.

表面海水中过氧化氢的存在与太阳辐射息息，其浓度在季节和日间变化。相对于许多细菌耐受的H2O2浓度，环境中的H2O2浓度较低，但是相对于细菌而言，海洋第1组crenarchaeota（MG1C）似乎缺乏针对该细菌的防御能力。因此，如果没有开发出降低H2O2毒性的替代策略，例如，通过消除，取代，更换或保护H2O2中毒易感性的结构中的敏感靶标的H2O2毒性，H2O2的光区浓度可能足以抑制MG1C代谢。鉴于仅测序了2个MG1C基因组，并且这些序列尚未完全注释，更不用说经过实验验证了注释，因此很难从基因组证据中推断出MG1C是否具有其他适应环境中的H2O2。因此，该项目将通过结合介质浮游生物组合的毒性生物测定与微型摄影型 - 荧光 - 荧光原位杂交（MAR-FISH）来识别目标群来识别目标群，从而直接通过测试MG1C对H2O2的敏感性来直接解决这个问题。如果提出的实验验证了MG1C对H2O2敏感，则MG1C的这种属性可以回答许多问题。 1）MG1C的全球和季节性分布 - 为什么它们不生活在地面层中；他们的季节性分布高纬度；它们的分布相对于EuryArchaeota，它们具有更多的过催化酶和过氧化物酶，并且在地表水和近岸环境中更为常见。 2）底物利用率和代谢模式 - 如果它们对其敏感，则MG1C只能使用底物或通过不生成H2O2的途径代谢。 3）缺乏古细菌病原体 - 一系列活性氧（ROS）是动物宿主对病原体的第一道防线。 4）为什么MG1C很难培养 - 许多标准实验室实践会产生ROS；这可能适用于也很难培养的细菌，因为并非所有细菌都有过氧化氢酶或过氧化物酶基因。 5）细菌与古细菌之间的差异 - 过氧化物敏感性可能是由于“冷冻代谢事故”导致的，这是古细菌光合作用发生的，这是古细菌生物化学的基本特性。 6）细菌和古细菌之间的某些生化和组成差异 - 某些细菌适应高腐蚀生活方式的一种方法是消除或保护其细胞机械中的ROS目标。这是一个有限的范围和预算的试点项目。尽管如此，它将直接为研究生和本科教育做出贡献。结果将通过会议和课堂上的出版物和演示进行传播，并且将根据NSF的数据发布政策公开提供数据。尽管问题很重要，并且有利于假设的论点和证据是挑衅和令人信服的，但它们是间接的，投机性的，不会通过同行评审的考验。但是，该假设的含义是变革性的，该项目将允许对该假设进行有限的检验。