中文摘要：

在青岛太平湾潮间带沉积物中发现了一定量的海洋趋磁细菌，最大丰度可达350个/cm^3。透射电镜观察发现该区域趋磁细菌均为趋磁球菌。磁小体个体形状单一，皆是立方体状；磁小体排列方式多样，以链状排列为主，包括单链、双链与多链，也有少数成簇排列。EDS结果表明，磁小体成分为四氧化三铁。据估算，趋磁细菌的铁元素含量（干重）范围在0.40%-6.91%之间，平均为2.19%。通过16S rRNA基因文库的构建与测序得到了47个趋磁细菌序列，分属13个OTU。系统发育分析结果表明，它们都属于α-变形菌纲，其中9个OTU与已知最相似序列的相似性低于97%，有5个OTU与已知最相似序列的相似性低于93%，可能代表了趋磁细菌的9个新种、5个新属，说明该区域潜在的微生物新种质资源十分可观。

英文摘要：

Abstract： Magnetotactic bacteria （MTB） are gram-negative motile prokaryotes that produce magnetosomes and can orient and migrate along the geomagnetic lines of force. They are ubiquitous in sediments and stratified water columns, distributed predominantly in the oxic-anoxic transition zone （OATZ）. MTB comprise several morphological types, including cocci, rods, vibrios, spirilla, and multicellular magnetotactic prokaryotes. Usually, cocci are the dominant morphology. Variable phylogenetic relatedness of MTB has been confirmed on the basis of 16S rRNA genes. MTB can biomineralize iron oxide and/or iron sulfide magnetosomes. In most MTB, magnetosomes are organized in chain（s）. In this study, we found a certain amount of MTB in the intertidal zone of Taiping Bay, Qingdao City, where the maximum abundance reaches up to 350 ind./cm^3. Transmission electron microscopy revealed that all the MTB were magnetotactic cocci, with a size of （2.23±0.69） μm×（1.84±0.47） μm and the width/length ratio of 0.87±0.10 （n=21）. Fifty-four percent of the MTB contained two chains of magnetosomes, eighteen percent with one chain, fourteen percent with more than two chains and fourteen percent with cluster. All of these magnetosomes were prismatic mineral crystals. There were 7-43 （mean=18,n=21） magnetosomes in a cell and the volume of magnetosomes varied between 2.71×10^5 nm^3 and 1.63×10^6 nm^3. Assuming that all the magnetosomes were magnetite, the percentage of Fe in MTB was 0.40%-6.91% （average 2.19%） and per square kilometer of intertidal zone produced 1.92 kg magnetite every year. This suggests that MTB may play an important role in the iron biogeochemical cycle in this area. Additionally, according to the statistics for each magnetotactic bacterium, we observed that the mass of magnetosome increased with the increasing mass of MTB （r=0.637,P=0.002 〈 0.05）. Phylogenetic analysis based on 16S rRNA gene sequences revealed that 47 sequences of MTB belonged to 13 OTUs （XCQD1-18, 1-2, 1-1