Diversity Of Magnetotactic Bacteria Research Articles

External magnetic field have significant effects on diversity of magnetotactic bacteria in sediments from Yangtze River, Chagan Lake and Zhalong Wetland in China

Magnetotactic bacteria (MTB) can rapidly relocate to optimal habitats by magnetotaxis, and play an important role in iron biogeochemical cycling. This study aimed to evaluate the contribution of the external magnetostatic field to the diversity of MTB in freshwater sediments from Yangtze River (Changjiang River, CJ), Chagan Lake (CGH) and Zhalong Wetland (ZL). The magnetic field intensity was tightly associated with the community richness of MTB in CJ, whereas it was closely related to the diversity of MTB in CGH and ZL (p < 0.05), elucidating a significant variation in the community composition of MTB. Magnetic exposure time appeared more significant correlation with community richness than diversity for MTB in CJ and CGH (p < 0.05), while an opposite relationship existed in ZL (p < 0.01). Herbaspirillum (93.81–96.48 %) dominated in the sediments of these surfacewatesr regardless of waterbody types, while it shifted to Magnetospirillum in ZL under 100 Gs magnetic field. The network connectivity and stability of MTB deteriorate with the increase of magnetic field intensity. Functional analysis showed that the Two-component system and ABC transporter system of MTB obviously responded to magnetic field intensity and exposure time. Our findings will pave the way to understanding the response mechanism of MTB community in freshwater sediments to the external magnetostatic field.

Magnetotactic bacteria in vertical sediments of volcanic lakes in NE China appear Alphaproteobacteria dominated distribution regardless of waterbody types.

Magnetotactic bacteria (MTB) distribute widely in sediment habitats and play critical roles in iron cycling. Here, the vertical distribution of morphology and phylogenetic diversity of MTB in sediments (0-15cm) of three lakes (open waterbody, Bailonghu, BL; semi-enclosed waterbody, Yaoquanhu, YQ; enclosed waterbody, Yueyapao, YY) in Wudalianchi volcanic field (China) were investigated. TEM showed the appearance of coccoid, rod-shaped, oval-shaped, and arc-shaped MTB. With the increase of BL sediment depth, the number of rod-shaped and spherical MTB decreased and increased, respectively. High-throughput sequencing indicated that Alphaproteobacterial MTB dominantly thrived in these lakes regardless of waterbody types. In BL and YY, the dominant genus was Magnetospirillum (44.99-70.80%) which showed a peak in the middle layer. In YQ, the genus Magnetospira was dominant in the upper (52.36%) and middle (66.56%) layer and Magnetococcus (69.63%) existed dominantly in the bottom layer. The vertical distribution of MTB in sediments of these lakes decreased first and then increased. Functional analysis showed that ABC transporter and two-component system of MTB changed significantly with the sediment depth. RDA indicated that the distribution of Magnetospirillum was positively associated with sulfide, pH, and TC. These findings will expand our knowledge of the vertical distribution of MTB in volcanic lakes.

Biogeochemical Niche of Magnetotactic Cocci Capable of Sequestering Large Polyphosphate Inclusions in the Anoxic Layer of the Lake Pavin Water Column.

Magnetotactic bacteria (MTB) are microorganisms thriving mostly at oxic–anoxic boundaries of aquatic habitats. MTB are efficient in biomineralising or sequestering diverse elements intracellularly, which makes them potentially important actors in biogeochemical cycles. Lake Pavin is a unique aqueous system populated by a wide diversity of MTB with two communities harbouring the capability to sequester not only iron under the form of magnetosomes but also phosphorus and magnesium under the form of polyphosphates, or calcium carbonates, respectively. MTB thrive in the water column of Lake Pavin over a few metres along strong redox and chemical gradients representing a series of different microenvironments. In this study, we investigate the relative abundance and the vertical stratification of the diverse populations of MTB in relation to environmental parameters, by using a new method coupling a precise sampling for geochemical analyses, MTB morphotype description, and in situ measurement of the physicochemical parameters. We assess the ultrastructure of MTB as a function of depth using light and electron microscopy. We evidence the biogeochemical niche of magnetotactic cocci, capable of sequestering large PolyP inclusions below the oxic–anoxic transition zone. Our results suggest a tight link between the S and P metabolisms of these bacteria and pave the way to better understand the implication of MTB for the P cycle in stratified environmental conditions.

A Novel Magnetotactic Alphaproteobacterium Producing Intracellular Magnetite and Calcium-Bearing Minerals.

Magnetotactic bacteria (MTB) are prokaryotes that form intracellular magnetite (Fe3O4) or greigite (Fe3S4) nanocrystals with tailored sizes, often in chain configurations. Such magnetic particles are each surrounded by a lipid bilayer membrane, called a magnetosome, and provide a model system for studying the formation and function of specialized internal structures in prokaryotes. Using fluorescence-coupled scanning electron microscopy, we identified a novel magnetotactic spirillum, XQGS-1, from freshwater Xingqinggong Lake, Xi'an City, Shaanxi Province, China. Phylogenetic analyses based on 16S rRNA gene sequences indicate that strain XQGS-1 represents a novel genus of the Alphaproteobacteria class in the Proteobacteria phylum. Transmission electron microscopy analyses reveal that strain XQGS-1 forms on average 17 ± 3 magnetite magnetosome particles with an ideal truncated octahedral morphology, with an average length and width of 88.3 ± 11.7 nm and 83.3 ± 11.0 nm, respectively. They are tightly organized into a single chain along the cell long axis close to the concave side of the cell. Intrachain magnetic interactions likely result in these large equidimensional magnetite crystals behaving as magnetically stable single-domain particles that enable bacterial magnetotaxis. Combined structural and chemical analyses demonstrate that XQGS-1 cells also biomineralize intracellular amorphous calcium phosphate (2 to 3 granules per cell; 90.5- ± 19.3-nm average size) and weakly crystalline calcium carbonate (2 to 3 granules per cell; 100.4- ± 21.4-nm average size) in addition to magnetite. Our results expand the taxonomic diversity of MTB and provide evidence for intracellular calcium phosphate biomineralization in MTB. IMPORTANCE Biomineralization is a widespread process in eukaryotes that form shells, teeth, or bones. It also occurs commonly in prokaryotes, resulting in more than 60 known minerals formed by different bacteria under wide-ranging conditions. Among them, magnetotactic bacteria (MTB) are remarkable because they might represent the earliest organisms that biomineralize intracellular magnetic iron minerals (i.e., magnetite [Fe3O4] or greigite [Fe3S4]). Here, we report a novel magnetotactic spirillum (XQGS-1) that is phylogenetically affiliated with the Alphaproteobacteria class. In addition to magnetite crystals, XQGS-1 cells form intracellular submicrometer calcium carbonate and calcium phosphate granules. This finding supports the view that MTB are also an important microbial group for intracellular calcium carbonate and calcium phosphate biomineralization.

Characterization and diversity of magnetotactic bacteria from sediments of Caroline Seamount in the Western Pacific Ocean

Characterization and diversity of magnetotactic bacteria from sediments of Caroline Seamount in the Western Pacific Ocean

Biodiversity of magnetotactic bacteria in the tropical marine environment of Singapore revealed by metagenomic analysis

Most studies on the diversity of magnetotactic bacteria (MTB) have been conducted on samples obtained from the Northern or the Southern hemispheres. The diversity of MTB in tropical Asia near the geo-equator, with a close-to-zero geomagnetic inclination, weak magnetic field and constantly high seawater temperature has never been explored. This study aims to decipher the diversity of MTB in the marine environment of Singapore through shotgun metagenomics. Although MTB has been acknowledged to be ubiquitous in aquatic environments, we did not observe magnetotactic behaviour in the samples. However, we detected the presence and determined the diversity of MTB through bioinformatic analyses. Metagenomic analysis suggested majority of the MTB in the seafloor sediments represents novel MTB taxa that cannot be classified at the species level. The relative abundance of MTB (~0.2–1.69%) in the samples collected from the marine environment of Singapore was found to be substantially lower than studies for other regions. In contrast to other studies, the genera Magnetovibrio and Desulfamplus, but not Magnetococcus, were the dominant MTB. Additionally, we recovered 3 MTB genomic bins that are unclassified at the species level, with Magnetovibrio blakemorei being the closest-associated genome. All the recovered genomic bins contain homologs of at least 5 of the 7 mam genes but lack homologs for mamI, a membrane protein suggested to take part in the magenetosome invagination. This study fills in the knowledge gap of MTB biodiversity in the tropical marine environment near the geo-equator. Our findings will facilitate future research efforts aiming to unravel the ecological roles of MTB in the tropical marine environments as well as to bioprospecting novel MTB that have been adapted to tropical marine environments for biotechnological applications.

A Review on Magnetotactic Bacteria and Magnetosomes: Recent Trends and Multivalent Advances

Magnetosome are forthwith one of the potential biosolutions for researchers exploring different aspects related to biomedical and biotechnology applications. Magnetotactic bacteria (MTB) are members of prokaryotes. They appear in different morphoforms and produce unique organelles called Magnetosomes (MS). The magnetosomes help bacteria in survival through imparting unique properties to navigate across the earth's geomagnetic field. The whole bacteria as well as magnetosomes prove suitable tool for multivalent applications, thus they turn out to be a challenge to researchers with respect to production yield. The discovery of a new wild type, magnetosome-over producing MTB strains allowing higher yield of magnetic nanoparticles is therefore critically needed to achieve a sustainable production of biologically derived magnetic nanoparticles. Therefore, is the necessity to explore biota in search of magnetotatic bacteria, and subsequently their multifaceted metabolism and iron-biomineralization process. Through this review, we focus on the diversity of Magnetotactic bacteria and their potential applications of magnetosomes in different sectors including biomedicine. Various research on this study is to emphasize the wide range of applications of these bionanomagnets in biomedical research, as well as recent breakthroughs and future research directions using magnetotactic bacteria in biomedicine.

Expanding magnetic organelle biogenesis in the domain Bacteria

BackgroundThe discovery of membrane-enclosed, metabolically functional organelles in Bacteria has transformed our understanding of the subcellular complexity of prokaryotic cells. Biomineralization of magnetic nanoparticles within magnetosomes by magnetotactic bacteria (MTB) is a fascinating example of prokaryotic organelles. Magnetosomes, as nano-sized magnetic sensors in MTB, facilitate cell navigation along the local geomagnetic field, a behaviour referred to as magnetotaxis or microbial magnetoreception. Recent discovery of novel MTB outside the traditionally recognized taxonomic lineages suggests that MTB diversity across the domain Bacteria are considerably underestimated, which limits understanding of the taxonomic distribution and evolutionary origin of magnetosome organelle biogenesis.ResultsHere, we perform the most comprehensive metagenomic analysis available of MTB communities and reconstruct metagenome-assembled MTB genomes from diverse ecosystems. Discovery of MTB in acidic peatland soils suggests widespread MTB occurrence in waterlogged soils in addition to subaqueous sediments and water bodies. A total of 168 MTB draft genomes have been reconstructed, which represent nearly a 3-fold increase over the number currently available and more than double the known MTB species at the genome level. Phylogenomic analysis reveals that these genomes belong to 13 Bacterial phyla, six of which were previously not known to include MTB. These findings indicate a much wider taxonomic distribution of magnetosome organelle biogenesis across the domain Bacteria than previously thought. Comparative genome analysis reveals a vast diversity of magnetosome gene clusters involved in magnetosomal biogenesis in terms of gene content and synteny residing in distinct taxonomic lineages. Phylogenetic analyses of core magnetosome proteins in this largest available and taxonomically diverse dataset support an unexpectedly early evolutionary origin of magnetosome biomineralization, likely ancestral to the origin of the domain Bacteria.ConclusionsThese findings expand the taxonomic and phylogenetic diversity of MTB across the domain Bacteria and shed new light on the origin and evolution of microbial magnetoreception. Potential biogenesis of the magnetosome organelle in the close descendants of the last bacterial common ancestor has important implications for our understanding of the evolutionary history of bacterial cellular complexity and emphasizes the biological significance of the magnetosome organelle.AvdtuUL8bNKQaZ224H3AxpVideo

Biodiversity of Magnetotactic Bacteria in the Freshwater Lake Beloe Bordukovskoe, Russia

According to 16S rRNA gene- or genome-based phylogeny, magnetotactic bacteria (MTB) belong to diverse taxonomic groups. Here we analyzed the diversity of MTB in a sample taken from the freshwater Lake Beloe Bordukovskoe near Moscow, Russia, by using molecular identification based on sequencing of the 16S rRNA gene and mamK, a specific marker gene for these bacteria. A protein encoded by the mamK gene is involved in magnetosome chain arrangement inside the cell. As a result, six operational taxonomic units (OTUs) of MTB were identified. Among them, OTUs affiliated with the phylum Nitrospirae were predominant. ‘Ca. Etaproteobacteria’ and Alphaproteobacteria represented the minor groups of MTB. We also identified a novel MTB belonging to the family Syntrophaceae of the Deltaproteobacteria class. Using a combination of fluorescence and transmission electron microscopy, the bacteria belonging to these new MTB groups were visualized. Electron microscopy revealed that Syntrophaceae MTB were rod-shaped and synthesized elongated magnetosomes, arranged as a disorganized cluster. Among the Nitrospirae group, two groups with vibrioid cell shape and one group of ovoid-shaped bacteria were identified, all of which had elongated magnetosome crystals consisting of magnetite.

Magnetotactic bacteria: Characteristics and environmental applications

Magnetotactic bacteria (MTB) are a group of Gram-negative prokaryotes that respond to the geomagnetic field. This unique property is attributed to the intracellular magnetosomes, which contains membrane-bound nanocrystals of magnetic iron minerals. This review summarizes the most recent advances in MTB, magnetosomes, and their potential applications especially the environmental pollutant control or remediation. The morphologic and phylogenetic diversity of MTB were first introduced, followed by a critical review of isolation and cultivation methods. Researchers have devoted to optimize the factors, such as oxygen, carbon source, nitrogen source, nutrient broth, iron source, and mineral elements for the growth of MTB. Besides the applications of MTB in modern biological and medical fields, little attention was made on the environmental applications of MTB for wastewater treatment, which has been summarized in this review. For example, applications of MTB as adsorbents have resulted in a novel magnetic separation technology for removal of heavy metals or organic pollutants in wastewater. In addition, we summarized the current advance on pathogen removal and detection of endocrine disruptor which can inspire new insights toward sustainable engineering and practices. Finally, the new perspectives and possible directions for future studies are recommended, such as isolation of MTB, genetic modification of MTB for mass production and new environmental applications. The ultimate objective of this review is to promote the applications of MTB and magnetosomes in the environmental fields.

Phylogenetic and Structural Identification of a Novel Magnetotactic Deltaproteobacteria Strain, WYHR-1, from a Freshwater Lake.

Magnetotactic bacteria (MTB) are phylogenetically diverse prokaryotes that are able to biomineralize intracellular, magnetic chains of magnetite or greigite nanocrystals called magnetosomes. Simultaneous characterization of MTB phylogeny and biomineralization is crucial but challenging because most MTB are extremely difficult to culture. We identify a large rod, bean-like MTB (tentatively named WYHR-1) from freshwater sediments of Weiyang Lake, Xi'an, China, using a coupled fluorescence and scanning electron microscopy approach at the single-cell scale. Phylogenetic analysis of 16S rRNA gene sequences indicates that WYHR-1 is a novel genus from the Deltaproteobacteria class. Transmission electron microscope observations reveal that WYHR-1 cells contain tens of magnetite magnetosomes that are organized into a single chain bundle along the cell long axis. Mature WYHR-1 magnetosomes are bullet-shaped, straight, and elongated along the [001] direction, with a large flat end terminated by a {100} face at the base and a conical top. This crystal morphology is distinctively different from bullet-shaped magnetosomes produced by other MTB in the Deltaproteobacteria class and the Nitrospirae phylum. This indicates that WYHR-1 may have a different crystal growth process and mechanism from other species, which results from species-specific magnetosome biomineralization in MTB.IMPORTANCE Magnetotactic bacteria (MTB) represent a model system for understanding biomineralization and are also studied intensively in biogeomagnetic and paleomagnetic research. However, many uncultured MTB strains have not been identified phylogenetically or investigated structurally at the single-cell level, which limits comprehensive understanding of MTB diversity and their role in biomineralization. We have identified a novel MTB strain, WYHR-1, from a freshwater lake using a coupled fluorescence and scanning electron microscopy approach at the single-cell scale. Our analyses further indicate that strain WYHR-1 represents a novel genus from the Deltaproteobacteria class. In contrast to bullet-shaped magnetosomes produced by other MTB in the Deltaproteobacteria class and the Nitrospirae phylum, WYHR-1 magnetosomes are bullet-shaped, straight, and highly elongated along the [001] direction, are terminated by a large {100} face at their base, and have a conical top. Our findings imply that, consistent with phylogenetic diversity of MTB, bullet-shaped magnetosomes have diverse crystal habits and growth patterns.

Distribution and diversity of magnetotactic bacteria in sediments of the Yellow Sea continental shelf

Magnetotactic bacteria (MTB) are cosmopolitan and ubiquitous in sediments of freshwater and marine habitats. Most studies of marine MTB have concerned intertidal zones, and there have been few reports of MTB from seafloor sediments. The objective of this study was to investigate the diversity and spatial distribution of MTB on the continent shelf of the Yellow Sea. Sediments from the continental shelf were collected from the Yellow Sea in August 2015 (summer) and January 2016 (winter). Magnetotactic bacteria were enriched by a permanent magnet. The number of MTB was counted. The diversity of MTB was identified based on high-throughput sequencing and Silva database and nt/nr database. Environmental factors including bottom temperature and salinity, total carbon (TC), total nitrogen (TN), total sulfur (TS), total organic carbon (TOC), concentration of iron, and the sediment grain size were measured. Magnetotactic bacteria were distributed widely in the Yellow Sea, at abundances of 5–2400 ind./dm3 in summer and 5–820 ind./dm3 in winter. The dominant MTB at most sampling stations were cocci, although rod-shaped MTB dominated at one station (H17). High-throughput sequencing distinguished 2669 reads for putative MTB in summer and 3271 in winter, and these were classified into 72 operational taxonomic units (OTUs). In both summer and winter, most reads (> 74%) and OTUs (> 50%) of putative MTB belonged to the Nitrospirae. The MTB abundance was significantly correlated with sediment grain size. The MTB abundance was highest at station H17, where the sediment grain size was larger than at other stations. We present a systematic assessment of the spatial distribution and diversity of MTB in sediments of the continental shelf of the Yellow Sea. Our data suggest that diverse MTB are widely distributed in the seafloor sediment of the Yellow Sea, with Nitrospirae likely being the dominating group, and that the abundance of MTB are influenced by sediment grain size.

The chimeric nature of the genomes of marine magnetotactic coccoid-ovoid bacteria defines a novel group of Proteobacteria.

Magnetotactic bacteria (MTB) are a group of phylogenetically and physiologically diverse Gram-negative bacteria that synthesize intracellular magnetic crystals named magnetosomes. MTB are affiliated with three classes of Proteobacteria phylum, Nitrospirae phylum, Omnitrophica phylum and probably with the candidate phylum Latescibacteria. The evolutionary origin and physiological diversity of MTB compared with other bacterial taxonomic groups remain to be illustrated. Here, we analysed the genome of the marine magneto-ovoid strain MO-1 and found that it is closely related to Magnetococcus marinus MC-1. Detailed analyses of the ribosomal proteins and whole proteomes of 390 genomes reveal that, among the Proteobacteria analysed, only MO-1 and MC-1 have coding sequences (CDSs) with a similarly high proportion of origins from Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria and Gammaproteobacteria. Interestingly, a comparative metabolic network analysis with anoxic network enzymes from sequenced MTB and non-MTB successfully allows the eventual prediction of an organism with a metabolic profile compatible for magnetosome production. Altogether, our genomic analysis reveals multiple origins of MO-1 and M. marinus MC-1 genomes and suggests a metabolism-restriction model for explaining whether a bacterium could become an MTB upon acquisition of magnetosome encoding genes.

青岛太平湾潮间带趋磁细菌多样性

PDF HTML阅读 XML下载 导出引用 引用提醒 青岛太平湾潮间带趋磁细菌多样性 DOI: 10.5846/stxb201412012380 作者: 作者单位: 中国科学院海洋研究所 海洋生态与环境科学重点实验室;中国科学院大学,中国科学院海洋研究所 海洋生态与环境科学重点实验室,中国科学院海洋研究所 海洋生态与环境科学重点实验室,中国科学院海洋研究所 海洋生态与环境科学重点实验室,中国科学院海洋研究所 海洋生态与环境科学重点实验室,中国科学院海洋研究所 海洋生态与环境科学重点实验室,中国科学院海洋研究所 海洋生态与环境科学重点实验室,中国科学院海洋研究所 海洋生态与环境科学重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41276170，41206150，41330962）；国际海域资源调查与开发“十二五”项目（深海（微）生物资源勘探与资源潜力评价）（任务书编号：DY125-15-R-03） Diversity of magnetotactic bacteria in the intertidal zone of Taiping Bay, Qingdao Author: Affiliation: Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences; University of Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences,Key Laboratory of Marine Ecology and Environmental Sciences,Institute of Oceanology,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 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/cm3。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。 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./cm3. 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 2.71×105 nm3 and 1.63×106 nm3. 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, 1-19, 51, 81, 6, 2-2, 4-20, 34, 2-23, 53, 130, 1-21) and affiliated to Alphaproteobacteria. OTU XCQD1-18 containing 23 sequences had the highest dominance index (48.93%). In addition, 6, 5, 2, 2, 2 sequences belonged to OTU XCQD2-2, XCQD1-21, XCQD1-2, XCQD2-23, XCQD130, respectively. The other OTUs had only one sequence. Shannon's diversity index H' of MTB in Taiping Bay was 2.64nit, and Species Evenness J' was 0.71. Nine OTUs (XCQD 1-18, 1-2, 1-19, 81, 6, 4-20, 34, 2-23, 53) shared less than 97% 16S rRNA gene sequence similarity with the nearest known sequences, in which, five OTUs (XCQD 81, 4-20, 4, 2-23, 53) shared lower than 93%. It suggested that they represented 9 new species and 5 novel genera. Our results indicate that there were substantial potential microorganism resources in Taiping Bay. Compared to the MTB community in Huiquan Bay, a bay adjacent to Taiping Bay, here were two MTB OTUs discovered both in Taiping Bay and Huiquan Bay. Two MTB OTUs were shared. Jaccard similarity coefficient was 0.1053, indicating that although the two bays were close to each other, the MTB communities showed great differences. Comparison of the features of MTB in Taiping Bay with two French Mediterranean coasts, Six-Fours-les-Plages and Gulf of Fos, revealed that environmental factors may have a great influence on the diversity of MTB. It is assumed that community succession, seasonal variation, and environmental distinction may contribute to the low similarity between the MTB communities and features of different intertidal areas. Our results imply that further investigation on MTB in terms of their diversity is required. 参考文献 相似文献 引证文献

Diversity of magnetotactic bacteria from a French pristine Mediterranean area.

Magnetotactic bacteria synthesize intracellular magnetite and/or greigite magnetosome crystals. They play a significant role in both iron and sulfur cycles in sedimentary aquatic environments. To get insight into the bio-geochemical contribution of MTB, more studies concerning their ecology and their distribution in diverse habitats are necessary. The MTB community of an oil-industry polluted area of the French Mediterranean coast has been previously investigated. Here, we investigate the MTB community from coastal sediments of a Mediterranean pristine area using optical and transmission electron microscopy and phylogenetic analysis based on 16S rRNA gene sequences. A particularly high diversity of MTB was observed, with cocci phylogenetically distributed across the order Magnetococcales, including a novel cluster with sequences from the Mediterranean Sea designated as "Med group", and novel morphotypes.

Clone libraries and single cell genome amplification reveal extended diversity of uncultivated magnetotactic bacteria from marine and freshwater environments

Magnetotactic bacteria (MTB), which orient along the earth's magnetic field using magnetosomes, are ubiquitous and abundant in marine and freshwater environments. Previous phylogenetic analysis of diverse MTB has been limited to few cultured species and the most abundant and conspicuous members of natural populations, which were assigned to various lineages of the Proteobacteria, the Nitrospirae phylum as well as the candidate division OP3. However, their known phylogenetic diversity still not matches the large morphological and ultrastructural variability of uncultured MTB found in environmental communities. Here, we used analysis of 16S rRNA gene clone libraries in combination with microsorting and whole-genome amplification to systematically address the entire diversity of uncultured MTB from two different habitats. This approach revealed extensive and novel diversity of MTB within the freshwater and marine sediment samples. In total, single-cell analysis identified eight different phylotypes, which were only partly represented in the clone libraries, and which could be unambiguously assigned to their respective morphotypes. Identified MTB belonged to the Alphaproteobacteria (seven species) and the Nitrospirae phylum (two species). End-sequencing of a small insert library created from WGA-derived DNA of a novel conspicuous magnetotactic vibrio identified genes with highest similarity to two cultivated MTB as well as to other phylogenetic groups. In conclusion, the combination of metagenomic cloning and single cell sorting represents a powerful approach to recover maximum bacterial diversity including low-abundant magnetotactic phylotypes from environmental samples and also provides access to genomic analysis of uncultivated MTB.

Short‐term effects of temperature on the abundance and diversity of magnetotactic cocci

Temperature is one of the most important climate factors that can regulate the activity and growth of organisms. However, it is so far unclear how temperature influences the abundance and community composition of magnetotactic bacteria (MTB) that mineralize intracellular magnetite and/or greigite magnetosomes and play significant roles in the global iron cycling and sediment magnetization. To address this specific problem, in this study we have assessed the impact of temperature on freshwater magnetotactic cocci through laboratory microcosm simulations. Microcosms containing MTB were exposed to four constant temperatures ranging from 9°C to 37°C. After 10 days and 28 days of incubation, no significant differences in abundance were detected in microcosms at 9°C, 15°C, and 26°C (Student's t-test, P > 0.05); however, microcosms exposed to 37°C exhibited a significant decrease of magnetotactic cocci abundance (P < 0.05). Dendrogram analysis of community-amplified ribosomal DNA restriction analysis (community ARDRA) banding patterns distinguished the 37°C samples from samples at lower temperatures regardless of incubation periods. Furthermore, clone library analysis revealed that most of the operational taxonomic units (OTUs) detected in samples from 9°C to 26°C were absent from the 37°C microcosms, whereas six OTUs were exclusively detected in the 37°C samples. Community compositions from four incubation temperatures were further compared using statistical phylogenetic methods (UniFrac and LIBSHUFF), which revealed that the 37°C samples harbored phylogenetically distinct MTB communities compared to those found in 9°C, 15°C, and 26°C samples. Taken together, our results indicate that elevated temperature can influence the abundance and diversity of dominant members of magnetotactic cocci. This linkage further infers that the abundance and diversity of MTB (e.g., based on the fossil magnetosomes) may be useful in reconstruction of paleotemperature.

Diversity analysis of magnetotactic bacteria in Lake Miyun, northern China, by restriction fragment length polymorphism

Magnetotactic bacteria (MTB) synthesize intracellular nano-scale crystals of magnetite or greigite within magnetosomes. MTB are ubiquitous in limnic and marine environments. In order to understand the diversity of MTB better, sediment samples were examined from Lake Miyun near Beijing by restriction fragment length polymorphism (RFLP). First, in silico analysis was used to evaluate the effectiveness of 12 sets of restriction endonucleases for distinguishing MTB sequences retrieved from the GenBank database. It was found that the tested restriction endonucleases had different power in the ability to differentiate the operational taxonomic units (OTUs) of MTB. Specifically, of the 12 sets of enzymes, MspI plus RsaI was found to be the most effective for correctly differentiating the OTUs of selected MTB sequences and it could detect 16 OTUs with appropriate OTUmin and OTUmax values (96.7% and 97.7%, respectively). The MspI plus RsaI RFLP analysis was then utilized to investigate the diversity of MTB in Lake Miyun sediment and it identified 8 OTUs (74.5% of the whole library) as MTB. Among these, 5 were affiliated to Alphaproteobacteria, while the rest belonged to the Nitrospira phylum. Interestingly, OTUs C, D and I displayed 91.8–98.4% similarity to “ Magnetobacterium bavaricum”. Together, these results demonstrated that the MspI plus RsaI RFLP analysis was useful for studying the diversity and change in community composition of uncultivated MTB from environmental samples.

Does capillary racetrack-based enrichment reflect the diversity of uncultivated magnetotactic cocci in environmental samples?

The racetrack-based PCR approach is widely used in phylogenetic analysis of magnetotactic bacteria (MTB), which are isolated from environmental samples using the capillary racetrack method. To evaluate whether the capillary racetrack-based enrichment can truly reflect the diversity of MTB in the targeted environmental sample, phylogenetic diversity studies of MTB enriched from the Miyun lake near Beijing were carried out, using both the capillary racetrack-based PCR and a modified metagenome-based PCR approach. Magnetotactic cocci were identified in the studied sample using both approaches. Comparative studies showed that three clusters of magnetotactic cocci were revealed by the modified metagenome-based PCR approach, while only one of them (e.g. MYG-22 sequence) was detected by the racetrack-based PCR approach from the studied sample. This suggests that the result of capillary racetrack-based enrichment might have been biased by the magnetotaxis of magnetotactic bacteria. It appears that the metagenome-based PCR approach better reflects the original diversity of MTB in the environmental sample.

Combined Approach for Characterization of Uncultivated Magnetotactic Bacteria from Various Aquatic Environments

Both magnetic collection and "race track" purification techniques were highly effective for selective enrichment of magnetotactic bacteria (MTB) from complex communities, as suggested by amplified ribosomal DNA restriction analysis and denaturing gradient gel electrophoresis combined with sequence analysis of 16S rRNA genes. Using these purification methods, the occurrence and diversity of MTB in microcosms from various marine and freshwater environments were assayed by using a combined microscopic, molecular, and cultivation approach. Most microcosms were dominated by magnetotactic cocci. Consistently, the majority of retrieved 16S RNA sequences were affiliated with a distinct cluster in the Alphaproteobacteria. Within this lineage the levels of sequence divergence were <1 to 11%, indicating genus-level diversity between magnetotactic cocci from various microcosms, as well as between MTB from different stages of succession of the same microcosms. The community composition in microscosms underwent drastic succession during incubation, and significant heterogeneities were observed between microcosms from the same environmental sources. A novel magnetotactic rod (MHB-1) was detected in a sediment sample from a lake in northern Germany by fluorescence in situ hybridization. MHB-1 falls into the Nitrospira phylum, displaying 91% 16S rRNA sequence similarity to "Magnetobacterium bavaricum." In extensive cultivation attempts, we failed to isolate MHB-1, as well as most other MTB present in our samples. However, although magnetotactic spirilla were not frequently observed in the enrichments, 10 novel isolates of the genus Magnetospirillum which had not routinely been isolated in pure culture before were obtained.