MGII古菌的视紫红质基因水平转移和生态功能演化

Marine Group II (MGII) archaea are the most abundant heterotrophic archaea in ocean waters, significantly effecting global carbon cycle and ecosystem functions. It has been found that MGII are very abundant in shallow seawaters and dominate in the planktonic archaeal populations, but the abundance of them are much lower in deep seawaters. The proteorhodopsin coding genes (pop genes) are present in most MGII from photic zone while absent in MGII from deep ocean. The phenomenon that MGII mainly distribute in shallow water may be intimately associated with the function of the proteorhodopsin in MGII. The key scientific questions of this application are as follows: 1) When did the pop gene arise in MGII and how has it evolved? 2) How would the horizontal transfer of pop gene influence the ecological functions of MGII? The proposer has already acquired several metagenome-assembled genomes of MGII from surface to hadal waters in Mariana Trench. Based on the previous work, this application will test the following hypothesis: MGII evolved from deep ocean to shallow water and acquired pop gene through horizontal transfer, promoting the ecological competitiveness of MGII in shallow water. This application will combine the metagenomic and metatranscriptomic sequencings and Bayesian bioinformatics methods to determine the origin time and evolutionary processes of MGII, and to reveal the influence of pop genes on ecological functions of MGII and their evolutionary patterning.

MGII是海洋水体中最丰富的异养古菌类群，在全球碳循环和生态环境中具有极其重要的作用。已知在浅层海水中MGII极其丰富并在古菌群落中占主导地位，但在深层海水中其丰度却极低；真光层的MGII大多含有编码视紫红质的pop基因，而深海中的MGII不含有pop基因。MGII主要分布在浅层海水的现象可能与视紫红质的生态功能有着密切关系。本申请拟解决的关键科学问题为:1）pop基因在MGII中出现的时间及演化过程；2）pop基因水平转移对MGII生态功能的影响。申请人已获得马里亚纳海沟表层到深渊层的多个MGII基因组，通过分析提出以下假设:MGII由深海向上层水体进化过程中通过水平基因转移获得pop基因，提高了MGII在浅层海水中的生态竞争力。该申请拟通过宏基因组和宏转录组测序，结合贝叶斯生物信息学方法来判定MGII的起源时间和演化过程，并揭示pop基因对MGII生态功能的影响及其演化规律。

海洋浮游古菌Marine Group II （MGII）是全球海水中丰度最高的异养古菌，对全球碳循环有重要的影响。MGII主要分布在真光层，在表层海水中的丰度尤其高，这与视紫红质基因的功能密切相关，但是对于视紫红质基因在MGII的演化过程中的获得和生态功能目前仍所知甚少。本研究通过结合实验室培养、分子生物学和生物信息学方法，分析了马里亚纳海沟、珠江口和其他海域全球海水中的MGII的16S rRNA基因和宏基因组测序数据，得出了以下主要结论：（1）根据宏基因组分析获结果确认了MGIIc为科水平上的MGII类群，从马里亚纳海沟深渊层水体中获得了高质量的MGIIc的基因组，并将MGIIc作为一个新的科命名为Candidatus Qianlongarchaea bathyliensis fam. sp. nov.;（2）根据贝叶斯算法分析结果，MGII可能起源于距今18.5亿年左右，起源于大氧化事件之后与MGII的好氧代谢有关，并且MGII的祖先是中等嗜热的，其祖先的最适生长温度大约在60 ºC左右，MGIIc、MGIIb和MGIIa的最适生长温度分别在57 ºC、49 ºC和46 ºC左右，它们是从高温到低温的顺序进行演化的；（3）系统进化分析结果表明早期MGII的基因组中不存在视紫红质基因，而是在演化的过程中从变形杆菌、拟杆菌等海洋细菌中通过水平基因转移获得的，视紫红质基因的获得极大提高了MGII在表层海水的生存能力；（4）培养实验结果表明球形棕囊藻能在短时间内刺激MGII迅速增殖，表明MGII与浮游藻类之间存在密切的生态关系。在项目执行期间，已经发表一篇中文核心期刊，一篇SCI论文已接收，还有一篇SCI论文正在撰写中，培养一位博士研究生和一位硕士研究生。

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