Characterization of Mediterranean magnetotactic bacteria

Magnetotactic bacteria are a diverse group of motile prokaryotes that are ubiquitous in aquatic habitats and cosmopolitan in distribution. In this study, we collected magnetotactic bacteria from the Mediterranean Sea. A remarkable diversity of morphotypes was observed, including multicellular types that seemed to differ from those previously found in North and South America. Another interesting organism was one with magnetosomes arranged in a six-stranded bundle which occupied one third of the cell width. The magnetosome bundle was evident even under optic microscopy. These cells were connected together and swam as a linear entire unit. Magnetosomes did not always align up to form a straight linear chain. A chain composed of rectangle magnetosomes bent at a posi- tion with an oval crystal. High resolution transmission electron microscopy analysis of the crystal at the pivotal position suggested uncompleted formation of the crystal. This is the first report of Mediterranean magnetotactic bacteria, which should be useful for studies of biogeochemical cycling and geohistory of the Mediterranean Sea.     

The discovery of magnetotactic/magnetosensitive bacteria

Magnetotactic bacteria orient and migrate along magnetic field lines in aquatic habitats. The first     

Morphological and phylogenetic diversity of magnetotactic bacteria and multicellular magnetotactic prokaryotes from a mangrove ecosystem in the Sanya River,South China

Journal of Oceanology and Limnology - Magnetotactic bacteria (MTB) are morphologically and phylogenetically diverse prokaryotes commonly able to produce magnetic nanocrystals within intracellular...     

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

Journal of Oceanology and Limnology - Magnetotactic bacteria(MTB) are a group of microorganisms capable of orientating and swimming along magnetic fields because they contain intracellular...     

Characterization of dominant giant rod-shaped magnetotactic bacteria from a low tide zone of the China Sea

Magnetotactic bacteria are a group of Gram-negative bacteria that synthesize magnetic crystals, enabling them to navigate in relation to magnetic field lines. Morphologies of magnetotactic bacteria include spirillum, coccoid, rod, vibrio, and multicellular morphotypes. The coccid shape is generally the most abundant morphotype among magnetotactic bacteria. Here we describe a species of giant rod-shaped magnetotactic bacteria(designated QR-1) collected from sediment in the low tide zone of Huiquan Bay(Yellow Sea, China). This morphotype accounted for 90% of the magnetotactic bacteria collected, and the only taxonomic group which was detected in the sampling site. Microscopy analysis revealed that QR-1 cells averaged(6.71±1.03)×(1.54±0.20) m m in size, and contained in each cell 42–146 magnetosomes that are arranged in a bundle formed one to four chains along the long axis of the cell. The QR-1 cells displayed axial magnetotaxis with an average velocity of 70±28 mm/s. Transmission electron microscopy based analysis showed that QR-1 cells had two tufts of fl agella at each end. Phylogenetic analysis of the 16 S r RNA genes revealed that QR-1 together with three other rod-shaped uncultivated magnetotactic bacteria are clustered into a deep branch of A lphaproteobacteria.     

太阳磁场磁性指数的变化对南亚夏季风环流强度的影响

利用太阳黑子相对数资料,根据太阳磁场磁性特征建立了太阳磁场磁性指数时间序列,并利用NCEP/NCAR再分析资料建立了1948-2006年的南亚夏季风环流强度指数,对两者之间存在的可能相关关系作了分析。结果表明：太阳磁场磁性变化是激发南亚夏季风环流强度年代际变化的重要原因,当太阳北（南）半球磁场磁极为N（S）极为前导时,南亚夏季风环流强度较强,当太阳北（南）半球磁场磁极为S（N）极为前导时,南亚夏季风环流强度较弱,太阳磁场磁性强度的变化超前于南亚夏季风环流强度变化5年左右。两者之间的这种相关关系,为南亚夏季风环流强度年代际变化方面的预测提供了理论依据。     

Biocompatibility of marine magnetotactic ovoid strain MO-1 for in vivo application

Journal of Oceanology and Limnology - Magnetotactic bacteria are capable of biosynthesizing magnetic nanoparticles, also called magnetosomes, and swimming along magnetic field lines. The abilities...     

Occurrence and microscopic analyses of multicellular magnetotactic prokaryotes from coastal sediments in the Yellow Sea

Multicellular magnetotactic prokaryotes(MMPs) are a group of aggregates composed of 7-45 gram-negative cells synthesizing intracellular magnetic crystals.Although they are thought to be globally distributed,MMPs have been observed only in marine environments in America and Europe.Most MMPs share a rosette-like morphology and biomineralize iron sulfide crystals.In the present study,abundant MMPs were observed,with a density of 26 ind./cm3,in the sediments of a coastal lagoon,Lake Yuehu,in the Yellow Sea.Optical microscopy showed that all of them were rosette shaped with a diameter of 5.5±0.8 mm.Transmission electron microscopy revealed that these MMPs were composed of 10-16 ovoid cells and flagellated peritrichously.High-resolution transmission electron microscopy and energy dispersive X-ray analysis indicated that they biomineralized bullet-shaped magnetite crystals in highly organized parallel chains within which the magnetosomes were oriented in the same direction.This is the first report of MMPs from Asia and demonstrates the ubiquitous distribution of MMPs.     

Observations on a magnetotactic bacteria-grazing ciliate in sediment from the intertidal zone of Huiquan Bay,China

Journal of Oceanology and Limnology - Magnetotactic bacteria(MTB) are a group of prokaryotes having the ability to orient and swim along geomagnetic fi eld lines because they contain intracellular...     

Determination of Antarctic geoid by using global gravity field

With Chinese latest global gravity field model WDM94, the authors providethe geoid height and mean free-air gravity anomaly of Antarctica (The range of latitude is from—60° to—90°). In order to conclude and analyze the characters of Antarctic geoid roundly, the authors collect the latest oversea global gravity field model OSU91 (to degree and order 360) and JGMOSU (to degree and order 360), get the corresponding geoid height and mean free-air gravity anomaly. The results arecompared with the results got from WDM94, thus we get the difference. The standard deviation of geoid height between WDM94 and OSU91 is ± 1.90 re;the deviation of geoid between WDM9 and JGMOSU is ± 2.09 m. The standard deviation of mean gravity anomaly are±8.97 mGal and ± 9.32 mGal respectively.     

Determination of optimal grid opening width for herringbone water-sediment separation structures based on sediment separation efficiency

The herringbone water-sediment separation structure(HWSSS) was developed to prevent debris flows. This paper mainly focuses on evaluating the sediment separation efficiency of HWSSS in debris flow prevention and determining the grid opening width D, a crucial structure parameter for HWSSS design. Theoretical analysis on the total sediment separation rate Pt reveals that the efficiency of sediment separation is much related with sediment grain size distribution(GSD) and grid opening width. The lower limit of Pt is deduced from the perspective of safety consideration by transforming debris flow into sediment-laden flow. Hydraulic model tests were carried out. Based on the regression analysis of the experimental data, the quantitative relationships between Pt and D and GSD characteristic values were finally established. A procedure for determining optimal grid opening width is proposed based on these analyses. These results are of significance in evaluating sediment separation effect by HWSSS in debris flow prevention and contribute to a more explicit methodology for design of HWSSS.     

The ecological distributions of N, P utilizing bacteria and heterotrophic bacteria in the moderate hypoxia zone of the Changjiang Estuary

The distributions of N utilizing bacteria (denitrifying bacteria and ammonifying bacteria), P utilizing bacteria (organic phosphobacteria and inorganic phosphobacteria) and heterotrophic bacteria in the Changjiang Estuary, and the roles of main environmental factors in distributing bacteria, are explored with observations from two cruises in June and August 2006. Comparisons between the two important periods of initial hypoxia phase (June) and developed hypoxia phase (August) show differences in both bacterial distributions and the associated main environmental factors. First, the primary group of ammonifying bacteria has larger magnitude with spatial maximum value in the hypoxic stations related to sediment in August. The phosphobacterial abundance and detection rates in August are much lower than those in June, but the denitrifying bacterial abundance becomes greater in August. However, the difference of heterotrophic bacterial abundance between June and August is not obvious. Second, main environmental factors influencing bacteria vary from initial hypoxia phase to developed hypoxia phase. Two parameters (salinity and NO₃ ^?) in surface water and five environmental parameters (pH, salinity, PO₄ ^3?, NO₃ ^? and temperature) in bottom water and surface sediment play major roles in the bacterial abundance in June, while different parameter combinations (salinity and PO₄ ^?) in surface water and different parameter combinations (DO, DOC, NO₃ ^?, PO₄ ^3? and pH) in bottom water and surface sediment play major roles in August. Moreover, the bottom bacteria distributions in area south of 31°N are related to the position of the Taiwan Warm Current in June. The bacterial abundance and distribution may respond to the environmental change in the hypoxia processes of initial phase and developed phase. During the hypoxia processes, the whole structure of bacterial functional groups probably turns to different states, causing the recycling of nutrient regeneration and aggravating hypoxia regionally.     

Characteristics of magnetic anomalies over transform faults and interpretation of magnetic anomalies in the Davis Strait

Transform fault delineation is important for determining the direction of plate motion during sea floor spreading. The analysis of marine magnetic anomalies is one of the most powerful geophysical methods for this purpose. In this paper the characteristics of the magnetic anomalies over some transform fault zones in the North Pacific and in the North Atlantic are discussed. Form comparison of the characteristics of these magnetic anomalies over transform fault zones with those of the NE-SW anomaly zone in the Davis Strait., the latter anomaly zone is interpreted not as the expression of a transform fault zone caused by horizontal movement during sea floor spreading but as an anomaly zone caused by basalt and therefore is inferred to be the expression of a fault zone produced by vertical crustal movement during volcanic activities. We discuss here the identification and correlation of linear anomalies in the Davis Strait region, and propose our hypothesis on the spreading history of the Davis Strait.     

Molecular survey of sulphate-reducing bacteria in the deep-sea sediments of the west Pacific Warm Pool

The sulfate-reducing bacteria (SRB) community in the deep-sea sediments of the west Pacific Warm Pool (WP) was surveyed by molecular phylogenetic analyses using primers targeting the 16S rRNA gene fragments of SRB. Specific 16S rRNA gene libraries from five sediment layers (1-cm, 3-cm, 6-cm, 10-cm and 12-cm layer) of the 12-cm core of WP-0 were constructed. The clones in the five libraries were differentiated by restriction fragment length polymorphism (RFLP) and representative clones were selected to sequence. It was found that the clones fell into four groups, which were closest related to Desulfotomaculum, Desul- facinum, Desulfomonile and Desulfanuticus. Desulfacinum-like clones were only detected in the upper layers of the sediment core, whereas Desulfomonile-like clones were only present in the deeper layers. Fluorescence in situ hybridization (FISH) was further carried out to visualize and count the SRB and bacteria in the five sediment layers. It was found that SRB constituted only a small proportion of the bacteria community (0.34%-1.95%), it had the highest content in the 3-cm layer (1.95%) and had a depth- related decreasing tendency along the 12- cm core.     

浅析野外金的快速分析方法

该文选择野外快速测金的2种方法:氢醌容量法和目视比色法,从原理、试样分析、富集方法、吸附机理、解脱方式、试剂及分析手续几方面进行对比分析,着重对氢醌容量法作研究和完善工作。针对通过比对实验,确立分析测试条件,选择确定了快速、简便、经济的测试流程,并应用于样品测试,提高了检测速度。     

Comparison of the defluoridation efficiency of calcium phosphate and chitin in the exoskeleton of Antarctic krill

Calcium （Ca）, phosphorus （P）, and chitin are the main components of the exoskeleton of krill. Defluoridation of a solution of sodium fluoride （NaF） using calcium phosphate （Ca3（PO4）2） and chitin as defluoridation agents was studied. Orthogonal experiments were designed to find the optimum reaction conditions for defluoridation, to obtain the maximum defluoridation efficiency and fluoride removal capacity of calcium phosphate and chitin. At the same time, a comparison of the capacity of the two defluoridation agents was made. The results suggest that calcium phosphate has a far greater capability than chitin for the removal of fluoride （F） from water under similar reaction conditions. It is also suggested that Antarctic krill is likely to adsorb fluoride via compounds such as calcium phosphate, hydroxyapatite, and other compounds of Ca and P with the general form （Ca, X）x（PO4, HPO4, Y）y（OH, Z）z, in addition to chitin.     

Phylogenetic diversity of culturable bacteria in surface seawater from the Drake Passage,Antarctica

The Drake Passage is located between the Antarctic Peninsula and Tierra del Fuego in the south of South America. Surface seawater samples were collected at seven sites in the Drake Passage during the austral summer of 2012. The 16S rRNA sequences were analyzed from 187 isolated bacterial strains. Three phyla, 29 genera and 56 species were identified. The three phyla were Actinobacteria, Firmicutes and Proteobacteria; the Proteobacteria included α-Proteobacteria, β-Proteobacteria and γ-Proteobacteria. γ-Proteobacteria, Actinobacteria and Firmicutes were the dominant class or phyla in terms of quantity and species. Gram-positive bacteria (Actinobacteria and Firmicutes) accounted for 57.8% of all types identified. There were nine dominant genera, including Curtobacterium, Staphylococcus, and Halomonas, and 14 dominant species including Curtobacterium flaccumfaciens, Curtobacterium pusillum, and Staphylococcus sciuri. Of the strains identified, 87.2% were catalase positive or weakly positive.     

Variation of bacteria biomass and its possible controlling factors in the East China Sea

Two surveys were performed for determining bacteria biomass (BB), temperature, salinity, chlorophyll a (chl-a) and nutrient concentrations at 11 stations with three sampling depths in the high-incidence regions of red tide in the East China Sea (ECS) in the spring of 2006. Temperature and salinity increased from nearshore to offshore region and from high latitude to low latitude in the two cruises of 2006. BB were between 0.3–5.2 mgC m⁻³ (about 2.1 mgC m⁻³ on average) and 0.2–6.0 mgC m⁻³ (about 2.7 mgC m⁻³ on average) respectively in the two cruises. BB in the surface layer decreased from the Changjiang River estuary to high sea and from low latitude to high latitude. The results showed that bacterial growth was regulated by temperature, primary production and inorganic nutrient concentrations depending on different hydrographic conditions. In the surface and middle layers where the primary production can supply enough organic substrate, temperature was the main factor to control bacteria biomass. BB showed a good correlation between the surface and middle layers in both cruises. The distribution of nutrients during both cruises showed a similar decreasing trend from nearshore region and high latitude to offshore region and low latitude. High BB values were mainly recorded from samples in the middle layer where chl-a concentrations were also high, indicating primary production being strongly correlated with temperature over the ECS shelf. In the offshore area, phosphate and silicate became limiting factors for phytoplankton growth with indirect influence on BB. Bacteria played an important role in nitrogen regeneration process turning organic nitrogen to inorganic forms such as NH₄ ⁺. The increasing ratio of NH₄ ⁺/DIN could be a proof of that.     

Visual analysis of the evolution and focus in landslide research field

This paper analysed the evolution of landslide research and research foci in different countries. The data comprise 3105 landslide SCI articles published between January 1977 and June 2015 from the Web of Science. The data are extracted under interaction constraints of the journal title, category, and keywords. The complex network method is used for the analysis. First, from the perspective of topics and methods, the evolution is systematically assessed by generating a co-citation network of the articles and a semantic cluster analysis. Second, from the perspective of topics and landsliderelated disasters, the focus in different countries is discussed by generating co-occurrence networks. These networks are the co-occurrence of the countries and keywords, and the co-occurrence of countries and landslide-related disaster phrases. The main conclusions are as follows:(1) landslide susceptibility analysis and methods of machine learning are popular research topics and methods, respectively. The topics change through time, and the article output is influenced by increasing landslide-related disasters, increasing economic losses and casualties, a desire for a more complete and accurate landslide inventory, and the use of effective methods, such as geographical information Science(GIS) and machine learning.(2) The research focus in each country is related with the country-specific disasters or economic costs caused by landslides to some degree. In addition to Italy and the USA, China is the country most commonly affected by landslides, and it should develop its own landslide database and complete in-depth studies of disaster mitigation.     

Microclimate regulation efficiency of the rural homegarden agroforestry system in the Western Sichuan Plain,China

Traditional rural homegarden agroforestry systems(referred to as homegarden) in the Western Sichuan Plain of China are often referred to as "Linpan" in Chinese. These homegardens are usually composed of farm houses, trees, bamboos, and small patches of land for flowers, fruits and vegetables. Over the Western Sichuan Plain’s area of approximately 18,800 km~2, there were more than 200,000 homegardens, accommodating 72.5% of the region’s rural population. As a unique local, cultural, and ecological resource, homegardens continuously support peasant households with provisioning, regulation, and landscape ecosystem services. This study combined low height remote sensing used unmanned aerial vehicle(UAV) photography, field investigation, and instrument monitoring. We try to identify the composition and structural characteristics of homegardens, as well as climatic regulation effects of the different types of homegardens. Temperature data were collected both for summer(June to August 2016) and winter(December 2016 to February 2017). The result shows that:(1) the average area of homegardens was 0.67 ha(sizes ranging from 0.16 ha to 1.24 ha), and with vegetation coverage 43.5%-76.9%(including 310 plant species).(2)In comparision with outside the homegardens, the average temperature inside the homegardens was significantly lower in summer(approximately 0.31 ℃-0.90 ℃). Although, the lowest summer temperature was differentiatee in between 13:30-16:00. Especially, the thermal effects of the home gardens were ranged from 2.00℃-2.65℃ at high temperatures(≥30℃).(3) The cooling effect of homegardens were positively correlated(p0.05) with tree area(X_1), vegetation coverage(X_2), tree coverage(X_3), tree species(X_4), and tree biomassper unit area(X_5), and the contribution rate was represented by X_3X_4X_5X_2X_1.(4)This study indicates the major role of homegardens for climate regulation and energy efficiency, providing suggestions for homegarden transformation and construction planning for new rural communities.