松球型多细胞趋磁原核生物的特征及多样性

Multicellular Magnetotactic Prokaryotes (MMPs) are a novel model organism in the study of origin and evolution of prokaryote multicellularity. MMPs are a peculiar group of magnetotactic bacteria (MTB) assembled with the same phylotypic cells. Currently two morphotypes of MMP have been identified, including mulberry-like MMPs and pineapple-like MMPs. Recently we observed a novel morphotype of MMPs in intertidal sediments of the Yellow Sea in China. Because they exhibit an unique pinecone like morphology, we designate them as pinecone-like MMPs. They distinguish the well-known mulberry-like and pineapple-like MMPs not only from the perceptible different morphotypes but also from the absence of the conspicuous ping-pong motion commonly observed for all currently known MMPs. To better understand the feature of the multicellularity of the pinecone-like MMPs, we will analyze the architecture, cell-cell connection, division of individual cell and all-together as a unit, as well as motion behavior. To identify them and carry out phylogenetic analysis, we will sort the pinecone-like MMPs by micromanipulation, amplify their genome using multiple displacement amplification (MDA) and perform 16S rRNA gene and/or whole genome sequencing. We will characterize magnetosomes with respect to the morphology, chemical composition, their intracellular arrangement, and the genetic features of magnetosome island. We will combine ecological survey methods and phylogenetic analysis to get insight into the distribution and phylogenetic diversity of the pinecone-like MMPs. Taken together, this study not only contributes to the multicellularity of the pinecone-like MMPs, but also provides a new model organism for studying origin and evolution of multicellular prokaryotes.

多细胞趋磁原核生物（Multicellular magnetotactic prokaryotes，MMPs）是一类新型多细胞原核生物，可作为研究多细胞生物进化的模式生物。MMPs是以多细胞聚集体形式存在的特殊趋磁细菌，已知的MMPs有桑葚型和菠萝型两种形态。我们在黄海潮间带首次发现了一种新形态的MMPs，因光镜下的形态类似松球而命名为松球型MMPs。该MMPs无乒乓运动。本项目拟通过光镜、电镜和超薄切片观察分析，在分裂方式、形态特征和显微结构等方面，通过与桑葚型和菠萝型MMPs对比，解析其多细胞特征；结合显微操作和单细胞全基因组扩增技术获得其基因组；根据磁小体形态、成分、排列方式和磁小体岛特征，解析磁小体特征；结合生态调查手段和系统发育学分析，探究分布特征和种属多样性。对松球型MMPs的研究，不仅能够认识MMPs多细胞形态结构以及进化发育的多样性，也为探究原核生物多细胞性提供了新素材。

多细胞趋磁原核生物（Multicellular magnetotactic prokaryotes，MMPs）是一类新型多细胞原核生物，可作为研究多细胞生物进化的模式生物。MMPs是以多细胞聚集体形式存在的特殊趋磁细菌，已知的MMPs有桑葚型和菠萝型两种形态。我们在青岛潮间带首次发现了一种新形态的MMPs，此次在荣成月湖潮间带也发现这种新型态的MMPs，因光镜下的形态类似松球而命名为松球型MMPs。本项目通过光镜、电镜观察分析，确定该MMPs是由33 ± 5个细胞围绕一个中心呈辐射状排列而成的球体，直径为13.4 ± 1.3 µm；能够自发荧光；周生鞭毛；能够进行自由移动、旋转和漫步，但与其他两种形态的MMPs不同的是，该MMPs未观察到乒乓运动；对波长小于500 nm的光敏感，可进行避光运动；进行短轴分裂，分裂时呈心形扭转。在分裂方式、形态特征和显微结构等方面，通过与桑葚型和菠萝型MMPs对比，解析了其多细胞特征。结合显微操作和单细胞全基因组扩增技术获得其基因组，通过16S rRNA 序列分析，将该松球型 MMPs 鉴定为一个新属新种，确定了其系统进化地位。松球型MMPs含有子弹头形磁小体，其成分为Fe3O4，并在磁小体岛中找到与合成铁氧型磁小体相关的基因，进而解析了其磁小体特征。对松球型MMPs的研究，不仅能够认识MMPs多细胞形态结构以及进化发育的多样性，也为探究原核生物多细胞性提供了新素材。