多细胞趋磁原核生物的生理代谢及进化研究

Microorgnisms play an important role in bio-geochemical cycles of almost all elements. Sulfur is among the most abundant elements on the Earth. It is mainly present as pyrite or gypsum in rocks and sediments and as sulfate in seawater. At present, sulfate-reducing bacteria (SRB) are virtually the only bacteria recognized as being involved in the sulfur bio-geochemical cycle. In fact, SRB are ubiquitous in anoxic habitats, where they can obtain energy by oxidizing organic compounds while reducing sulfate to hydrogen sulfide. However, the marine sediments are covered by air-saturated seawater and at the oxic-anoxic interface harbor a variety of bacteria that can obtain free energy from the oxidization of reduced sulfur compounds via various metabolism pathways. Our objective is to use magnetotactic multicellular prokaryotes (MMPs) as a model and undertake single cells separation and genome amplification in combination with ecological survey, cultivation and genomic analysis to study the mechanism of biomineralization of sulfur into magnetic greigite nanocrystals. MMPs are micro-aerophilic and found only in marine sediments. They display magnetic polarity in organism structure, motility and reproduction, and there is no single cell state observed during their life cycle. Therefore, they are distinct from the three well known prokaryotic multicellular organisms: cyanobacteria, actinomycetes and myxobacteria. Hence, MMPs could be considered as the type IV multicellular prokaryotes. Taken together, we aim at studying the sulfur metabolism and evolution of bacterial multicellularity of MMPs, and from a novel angle to investigate the function played by bacteria in bio-geochemical cycles of sulfur and iron at the marine sediment-seawater interface.

微生物在元素的地化循环中发挥着重要的催化和调节作用。目前有关微生物参与海洋硫、碳循环的研究集中于厌氧硫酸盐还原菌。这类细菌通过异养代谢途径矿化有机碳，将硫酸盐转变成硫化物。同绝对厌氧条件相比，海底-水界面是微好氧环境。在这种生境中除硫酸盐还原菌外，还有其它微生物种群以不同的生理代谢方式参与硫的生物地化循环。此项目将以微好氧多细胞趋磁原核生物为模式菌，使用单细胞分离和DNA扩增技术，结合生态调查、细菌培养和基因组分析，研究将硫矿化成四硫化三铁型纳米磁颗粒的代谢途径。多细胞趋磁原核生物仅分布在海洋环境中。它们在结构、运动和繁殖过程中显示出特殊的磁场定位性，未发现单细胞阶段。这些特征有别于常见的蓝细菌、放线菌和粘细菌这三类多细胞原核生物，可视为第四类多细胞原核生物。此项目的特色是通过研究多细胞趋磁原核生物的生理代谢类型和进化机制，从新的角度探索认识沉积物-海水界面硫、铁元素的生物地化循环过程。

微生物在元素的地化循环中发挥着重要的催化和调节作用。目前有关微生物参与海洋硫、碳循环的研究集中于厌氧硫酸盐还原菌。这类细菌通过异养代谢途径矿化有机碳，将硫酸盐转变成硫化物。同绝对厌氧条件相比，海底-水界面是微好氧环境。在这种生境中除硫酸盐还原菌外，还有其它微生物种群以不同的生理代谢方式参与硫的生物地化循环。此项目以微好氧的多细胞趋磁原核生物为模式菌，使用单细胞显微操作离和基因组扩增技术，结合生态调查、细菌培养和基因组分析，研究多细胞趋磁原核生物将硫（氧）矿化成四硫（氧）化三铁型纳米磁颗粒的代谢途径。多细胞趋磁原核生物目前仅分布在海洋环境中，它们在细胞结构、运动形式和繁殖过程中显示出特殊的磁场定位性或导向性，且未发现单细胞阶段。这些特征有别于常见的蓝细菌、放线菌和粘细菌这三类公认的多细胞原核生物，可视为第四类多细胞原核生物。项目建立了多细胞趋磁原核生物的显微操作分离平台，与单细胞基因组扩增技术结合获得了3种多细胞趋磁原核生物的基因组；通过对基因组序列的注释和解析，对多细胞趋磁原核生物铁代谢产生磁小体的过程进行了机理研究，并对其参与铁地化循环的贡献进行了评估；通过对多细胞超微结构的观察探讨了其细胞分化程度和多细胞性，结合基因组分析和多细胞趋磁原核生物的原位培养生活史观察，探讨了多细胞趋磁原核生物的进化，证明其是一类新的多细胞原核生物。此项目的特色是通过研究多细胞趋磁原核生物的生理代谢类型和进化机制，从新的角度探索认识沉积物-海水界面硫、铁元素的生物地化循环过程。