Coliform bacteria (CB) can be used as an indicator of seawater quality. Long-term monitoring of seawater quality based on CB abundance is lacking in Jiaozhou Bay. In this study, CB abundance in surface seawater of 12 different stations in Jiaozhou Bay was investigated by culturing method. The results showed that: (1) the abundance of CB showed a decreasing tendency during the investigation. During 2004–2007, 2008–2013, and 2014–2017, the average CB abundance decreased significantly, forming a “three stages phenomenon”; (2) the average CB abundance in the first half of the year was lower than that in the second half; (3) the CB abundance in Jiaozhou Bay was spatially heterogeneous. The maximum average CB abundance was observed in the estuary area, and followed by the bay mouth area, the outer bay area, and the inner bay area. The highest abundance may be associated with sewage discharge related to human activities; (4) the abundance of CB was most positively correlated with the concentration of ammonium salt and nitrate, while most negatively correlated with salinity; (5) the years 2007 (2008) and 2013 (2014) were time points of the “three stages phenomenon.” These time points coincide with environmental governance actions, indicating that the actions have played a prominent role in improving seawater quality. Long-term survey of CB can not only serve as an indicator of seawater quality, but also provide a basis for the development of environmental governance strategies and pollution control.

荣成月湖是一个典型天然潟湖,潮间带沉积物中存在多种形态趋磁细菌.通过Roche 454高通量测序平台,对沉积物样品(B_S)和磁收样品(B_M)进行16S rRNA基因高通量测序,认识荣成潮间带沉积物的细菌群落结构,并了解趋磁细菌多样性及系统进化地位.研究结果表明沉积物样品中主要的细菌类群为δ-变形菌纲,占总细菌数的26.4％,其次是γ-变形菌纲和α-变形菌纲;而磁收样品中细菌多样性和种类明显降低,以α-变形菌纲占绝对优势,相对比例达72.6％.在磁收样品和沉积物样品分别发现了1612条和186条reads与趋磁细菌相关,分别占细菌总数的5.76％和0.85％,磁收样品中趋磁细菌数是沉积物样品的6.8倍.对两个样品中获得的趋磁细菌序列进行系统进化分析,发现这些序列多数属于变形菌门的 α-变形菌纲,以趋磁球菌占绝对优势,少数属于 δ-变形菌纲,与多细胞趋磁原核生物亲缘关系最近.海洋趋磁螺菌属仅在B_M样品中检出,趋磁弧菌属在B_M样品优势度高于B_S样品,而多细胞趋磁原核生物和趋磁螺菌属在B_S样品中优势度更高.通过分析样品间的差异OTUs,认为荣成潮间带沉积物中可能存在大量未知的趋磁细菌新类群.研究结果为下一步培养和开发趋磁细菌这一功能菌群,发现趋磁细菌新类群及趋磁细菌生态功能提供了基础资料.

A diversity of organisms can sense the geomagnetic field for the purpose of navigation. Magnetotactic bacteria are the most primitive magnetism-sensing organisms known thus far and represent an excellent model system for the study of the origin, evolution, and mechanism of microbial magnetoreception (or magnetotaxis). The present study is the first report focused on magnetosome gene cluster duplication in the Alphaproteobacteria , which suggests the important role of gene duplication in the evolution of magnetotaxis in the Alphaproteobacteria and perhaps the domain Bacteria . A novel scenario for the evolution of magnetotaxis in the Alphaproteobacteria is proposed and may provide new insights into evolution of magnetoreception of higher species.

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.

There are two genetically distinct morphological types of multicellular magnetotactic prokaryotes (MMPs) in the intertidal zone of Lake Yuehu (China): ellipsoidal MMPs (eMMPs) and spherical MMPs (sMMPs). We studied the vertical distribution of both types of MMPs in the sediment at Lake Yuehu during 1 year. Both types of MMPs were observed at sediment depths ranging from 1 to 34 cm, depending on the seasons. The eMMPs distributed at depths of 2-34 cm during spring, 1-11 cm during summer, 2-21 cm during autumn and 9-32 cm during winter. The eMMP species Candidatus Magnetananas rongchenensis, with magnetite magnetosomes, dominated at all distribution depths. These results suggested that Ca. M. rongchenensis migrated vertically during four seasons. The vertical profiles of oxidation-reduction potential (ORP) in Lake Yuehu changed seasonally, and these changes coincided with the seasonal distribution of MMPs, suggesting that the ORP affected the vertical distribution of MMPs. In addition, high concentrations of ammonium and silicate were associated with low abundances of MMPs.

Marine magnetotactic bacteria were collected from the intertidal sediments of Yuehu Lake (China), where their abundance reached 103–104 ind./cm3. Diverse morphotypes of magnetotactic bacteria were observed, including cocci and oval, vibrio-, spirillum-, rod-, elliptical-, handle- and bar-shaped forms. The magnetococci were the most abundant, and had flagella arranged in parallel within a bundle. The majority of magnetosomes were arranged in one, two or multiple chains, although irregular arrangements were also evident. All the results of high-resolution transmission electron microscopy (HRTEM) analysis show that magnetosome crystals were composed of Fe3O4, and their morphology was specific to particular cell morphotypes. By the 16S rRNA gene sequence analysis, we found fourteen operational taxonomic units (OTUs) which were related to magnetotactic bacteria. Among these, thirteen belonged to the Alphaproteobacteria and one to the Gammaproteobacteria. Compared with known axenic and uncultured marine magnetotactic bacteria, the 16S rRNA gene sequences of most magnetotactic bacteria collected from the Yuehu Lake exhibited sequence identities ranging from 90.1% to 96.2% (<97%). The results indicate that microbial communities containing previously unidentified magnetotactic bacteria occur in the Yuehu Lake.

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。

Magnetospira sp. QH-2 is a marine magnetotactic spirillum, isolated from the intertidal zone of the Yel-low Sea, China. The trait that its magnetosome chains display a relatively large size distribution is predicted to be related to the function of the mamK-encoded protein, namely, MamK. We find that mamK gene codes for 1086bp and MamK, which belong to the NBD_sugar-kinase_HSP70_actin superfamily, are composed of 361 amino acids and do not contain any trans-membrane domain. Based on the differences of the phylogenetic trees, we determine that the acquisition of magnetosome island and bacteria evolution are possibly two independent processes. While the morphology feature of magnetotactic spirillum both in fresh water and marine is similar, its phylogenetic status is different to some extent, which may indicate its adaptive evolutions.

A quantity of magnetotactic bacteria (MTB) were found in the intertidal zone of Tianyahaijiao, Sanya, China, where the maximum abundance can reach up to 100 ind./cm3. Transmission electron microscopy (TEM) re-vealed that most of the MTB were magnetotactic cocci, containing magnetosomes, which were prismatic mineral crystals, mostly organized in chain(s) (one or two chains), while some were in cluster. High-resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-ray Spectroscopy (EDXA) showed that the magnetosomes contained magnetite. It was estimated that the percentage of Fe found in the MTB was 0.70%~7.53% (average 2.05%). Phylogenetic analyses, based on 16S rRNA gene sequences, revealed that 16 sequences of MTB belonged to 9 operational taxonomic units (OTUs) and were affiliated to the class Alphaproteobacteria, except that one OTU was affiliated to the classGammaproteobacteria. Eight OTUs shared < 97% 16S rRNA gene sequence similarity with the nearest known sequences, in which 5 OTUs shared lower than 93% similarity. These results indicate that the MTB resources in Tianyahaijiao were considerable.

Multicellular magnetotactic prokaryotes (MMPs) are a peculiar group of magnetotactic bacteria, each comprising approximately 10-100 cells of the same phylotype. Two morphotypes of MMP have been identified, including several species of globally distributed spherical mulberry-like MMPs (s-MMPs), and two species of ellipsoidal pineapple-like MMPs (e-MMPs) from China (Qingdao and Rongcheng cities). We recently collected e-MMPs from Mediterranean Sea sediments (Six-Fours-les-Plages) and Drummond Island, in the South China Sea. Phylogenetic analysis revealed that the MMPs from Six-Fours-les-Plages and the previously reported e-MMP Candidatus Magnetananas rongchenensis have 98.5% sequence identity and are the same species, while the MMPs from Drummond Island appear to be a novel species, having > 7.1% sequence divergence from the most closely related e-MMP, Candidatus Magnetananas tsingtaoensis. Identification of the novel species expands the distribution of e-MMPs to Tropical Zone. Comparison of nine physical and chemical parameters revealed that sand grain size and the content of inorganic nitrogen (nitrate, ammonium and nitrite) in the sediments from Rongcheng City and Six-Fours-les-Plages were similar, and lower than found for sediments from the other two sampling sites. The results of the study reveal broad diversity and wide distribution of e-MMPs.

Two morphotypes (spherical and ellipsoidal) of multicellular magnetotactic prokaryotes (MMPs) have been reported from the sediments of Lake Yuehu, China. Here, their temporal distributions and their relationships with biogeochemical parameters are studied. Samples were collected at approximately 2-week intervals from two sites (A and B) during the period September 2012 to December 2013. The abundance of MMPs was high in summer and autumn, but low in winter and spring. Furthermore, the peaks in the numbers of the two types of MMPs were sequential, with the highest concentration of the spherical MMPs occurring prior to that of the ellipsoidal MMPs. This may be related to different optimal growth temperatures for the two types. Although the two types of MMP coexisted at both sites, their numbers were different; at most times, spherical MMPs dominated at site A, whereas ellipsoidal MMPs dominated at site B. Geochemical analysis revealed that the environmental conditions at site A varied more than at site B. Compared with the widely distributed spherical MMPs, ellipsoidal MMPs seemed to prefer more stable habitats. This is the first report of the temporal distribution of ellipsoidal MMPs in sediments, suggesting that their environmental adaptations differ from those of spherical MMPs.

Magnetotactic bacteria (MTB) are a group of Gram-negative bacteria synthesizing magnetic crystals that allow them aligning along magnetic field lines. They have diverse morphologies including cocci, rods, vibrio, spirilla, and multicellular magnetotactic prokaryotes (MMPs). MMPs are composed of 10-57 cells with peritrichous flagella on their outer surfaces and swim as an entire unit. Here, we describe a species of spherical MMPs isolated from intertidal sediments of Lake Yuehu (Yellow Sea, China). They were mainly found in the subsurface layer of gray-black sediments. Microscopy revealed that these spherical MMPs were 5.6 +/- 0.9 mu m in diameter and composed of approximately 16-32 ovoid cells with a helical arrangement and peritrichous flagellation. High-resolution transmission electron microscopy showed that the MMPs contained both bullet-shaped magnetite and irregular greigite magnetosomes that were arranged in chains or clusters. These MMPs displayed typical escape motility and negative phototaxis. The 16S rRNA genes of micromanipulation-purified spherical MMPs were cloned and sequenced. Phylogenetic analysis revealed that the MMP species was affiliated with Deltaproteobacteria and displayed >2.8% sequence divergence with respect to previously reported MMPs. This is the first phylogenetic identification of a spherical MMP that produces both magnetite and greigite magnetosomes. (C) 2014 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

Two morphotypes of multicellular magnetotactic prokaryotes (MMPs) have been identified: spherical (several species) and ellipsoidal (previously one species). Here, we report novel ellipsoidal MMPs that are ∼ 10 × 8 μm in size, and composed of about 86 cells arranged in six to eight interlaced circles. Each MMP was composed of cells that synthesized either bullet-shaped magnetite magnetosomes alone, or both bullet-shaped magnetite and rectangular greigite magnetosomes. They showed north-seeking magnetotaxis, ping-pong motility and negative phototaxis at a velocity up to 300 μm s(-1) . During reproduction, they divided along either their long- or short-body axes. For genetic analysis, we sorted the ellipsoidal MMPs with micromanipulation and amplified their genomes using multiple displacement amplification. We sequenced the 16S rRNA gene and found 6.9% sequence divergence from that of ellipsoidal MMPs, Candidatus Magnetananas tsingtaoensis and > 8.3% divergence from those of spherical MMPs. Therefore, the novel MMPs belong to different species and genus compared with the currently known ellipsoidal and spherical MMPs respectively. The novel MMPs display a morphological cell differentiation, implying a potential division of labour. These findings provide new insights into the diversity of MMPs in general, and contribute to our understanding of the evolution of multicellularity among prokaryotes.

Novel large, rod-shaped magnetotactic bacteria (MTB) were discovered in intertidal sediments of the Yellow Sea, China. They biomineralized more than 300 rectangular magnetite magnetosomes per cell. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that they are affiliated with the Alphaproteobacteria and may represent a new genus of MTB.