Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63-98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid "Alphaproteobacterium", as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 x 10(7) cells/cm3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6-60 microM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 microM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities.     

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.     

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.     

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.     

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

Microbiology - 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...     

Low Intraspecific Diversity in a Polynucleobacter Subcluster Population Numerically Dominating Bacterioplankton of a Freshwater Pond

Cultivation-dependent and -independent methods were combined to investigate the microdiversity of a Polynucleobacter subcluster population (Betaproteobacteria) numerically dominating the bacterioplankton of a small, humic freshwater pond. Complete coverage of the population by cultivation allowed the analysis of microdiversity beyond the phylogenetic resolution of ribosomal markers. Fluorescent in situ hybridization with two probes specific for the narrow subcluster C (PnecC bacteria) of the Polynucleobacter cluster revealed that this population contributed up to 60% to the total number of bacterioplankton cells. Microdiversity was investigated for a date at which the highest relative numbers of PnecC were observed. A clone library of fragments of the ribosomal operon (16S rRNA genes, complete 16S-23S internal transcribed spacer 1 [ITS1], partial 23S rRNA genes) amplified with universal bacterial primers was constructed. The library was stepwise screened for fragments from PnecC bacteria and for different ITS genotypes of PnecC bacteria. The isolated PnecC strains were characterized by sequencing of the 16S rRNA genes and the ITS1. Both the clone library and the established culture collection contained only the same three ITS genotypes, and one of them contributed 46% to the entire number of clones. Genomic fingerprinting of the isolates with several methods always resulted in the detection of only one fingerprint per ITS genotype. We conclude that a Polynucleobacter population with an extremely low intraspecific diversity and an uneven structure numerically dominated the bacterioplankton community in the investigated habitat. This low intraspecific diversity is in strong contrast to the high intraspecific diversities found in marine bacterial populations.     

Low intraspecific diversity in a polynucleobacter subcluster population numerically dominating bacterioplankton of a freshwater pond

Cultivation-dependent and -independent methods were combined to investigate the microdiversity of a Polynucleobacter subcluster population (Betaproteobacteria) numerically dominating the bacterioplankton of a small, humic freshwater pond. Complete coverage of the population by cultivation allowed the analysis of microdiversity beyond the phylogenetic resolution of ribosomal markers. Fluorescent in situ hybridization with two probes specific for the narrow subcluster C (PnecC bacteria) of the Polynucleobacter cluster revealed that this population contributed up to 60% to the total number of bacterioplankton cells. Microdiversity was investigated for a date at which the highest relative numbers of PnecC were observed. A clone library of fragments of the ribosomal operon (16S rRNA genes, complete 16S-23S internal transcribed spacer 1 [ITS1], partial 23S rRNA genes) amplified with universal bacterial primers was constructed. The library was stepwise screened for fragments from PnecC bacteria and for different ITS genotypes of PnecC bacteria. The isolated PnecC strains were characterized by sequencing of the 16S rRNA genes and the ITS1. Both the clone library and the established culture collection contained only the same three ITS genotypes, and one of them contributed 46% to the entire number of clones. Genomic fingerprinting of the isolates with several methods always resulted in the detection of only one fingerprint per ITS genotype. We conclude that a Polynucleobacter population with an extremely low intraspecific diversity and an uneven structure numerically dominated the bacterioplankton community in the investigated habitat. This low intraspecific diversity is in strong contrast to the high intraspecific diversities found in marine bacterial populations.     

Ultrastructure of a magnetotactic spirillum.

The ultrastructure of a magnetotactic bacterium (strain MS-1) was examined by transmission, scanning, and scanning-transmission electron microscopy. The organism resembled other spirilla in general cell morphology, although some differences were detected at the ultrastructural level. Electron-dense particles within magnetotactic cells were shown by energy-dispersive X-ray analysis to be localizations containing iron. A non-magnetotactic variant of strain MS-1 lacked these novel bacterial inclusion bodies. A chain of these particles traversed each magnetotactic cell in a specific arrangement that was consistent from cell to cell, seemingly associated with the inner surface of the cytoplasmic membrane. Each particle was surrounded by an electron-dense layer separated from the particle surface by an electron-transparent region. The term "magnetosome" is proposed for the electron-dense particles with their enveloping layer(s) as found in this and other magnetotactic bacteria.     

Identification and characterization of magnetotactic Gammaproteobacteria from a salt evaporation pool,Bohai Bay,China

Magnetotactic bacteria (MTB) are phylogenetically diverse prokaryotes that can produce intracellular chain-assembled nanocrystals of magnetite (Fe₃O₄) or greigite (Fe₃S₄). Compared with their wide distribution in the Alpha-, Eta- and Delta-proteobacteria classes, few MTB strains have been identified in the Gammaproteobacteria class, resulting in limited knowledge of bacterial diversity and magnetosome biomineralization within this phylogenetic branch. Here, we identify two magnetotactic Gammaproteobacteria strains (tentatively named FZSR-1 and FZSR-2 respectively) from a salt evaporation pool in Bohai Bay, at the Fuzhou saltern, Dalian City, eastern China. Phylogenetic analysis indicates that strain FZSR-2 is the same species as strains SHHR-1 and SS-5, which were discovered previously from brackish and hypersaline environments respectively. Strain FZSR-1 represents a novel species. Compared with strains FZSR-2, SHHR-1 and SS-5 in which magnetite particles are assembled into a single chain, FZSR-1 cells form relatively narrower magnetite nanoparticles that are often organized into double chains. We find a good relationship between magnetite morphology within strains FZSR-2, SHHR-1 and SS-5 and the salinity of the environment in which they live. This study expands the bacterial diversity of magnetotactic Gammaproteobacteria and provides new insights into magnetosome biomineralization within magnetotactic Gammaproteobacteria.     

Genetic survey on a reed-bed in Central Italy showing early die-back symptoms

Phragmites australis die-back is a well known phenomenon in Central Europe and rather recently observed also in some Mediterranean wetlands. In this study we analyze the genetic structure of a reed-bed in a protected wetland in N-W Tuscany (Italy) recently showing some clear symptoms of die-back, in particular the clumped growth-form, searching for any possible relationships with the ecological condition or the health status of common reed stands. After a diachronic analysis of vegetation maps (from 1988 to 2013) and a field survey, we have sampled four temporarily emerged and four permanent submerged reed stands, being the submersion regime a crucial trigger of reed die-back. Aquatic plots showed two clear conditions, with the presence of clumped and non-clumped stands. Emerged stands have been sampled in areas showing temporarily stable, increasing and decreasing reed-bed surface. In order to investigate the genetic structure of the population, the AFLP technique was applied on 69 individuals. The total reedbed surface showed a decrease in the observed time, partly due to the human activities and partly attributable to the RDBS. In several areas of the Lake the reed-bed appeared clumped and fragmented. The genetic analysis put in evidence a rather high level of genetic diversity, compared to the results of previous international studies on other populations of the same species. No significant differences between temporarily and permanently submerged stands were found. The major portion of genetic variation appeared within sampling sites rather than between sampling sites, indicating the absence of isolation between the different reed stands of the lake and a negligible role of genetic diversity in the occurrence of die-back symptoms.     

Simple pond restoration measures increase dragonfly (Insecta: Odonata) diversity

Ponds are home to a diverse community of specialized plants and animals and are hence of great conservation concern. Through land-use changes, ponds have been disappearing rapidly and remaining ponds are often threatened by contamination and eutrophication, with negative consequences for pond-dependent taxa like amphibians or dragonflies (Odonata: Anisoptera and Zygoptera). Increasingly, restoration measures such as removal of shading terrestrial vegetation or submerged organic matter are implemented to counteract current threats, but how these measures affect the target taxa is rarely assessed. We tested if and how simple pond restoration measures affectionate diversity. We propose that pond restoration influences the light regime, which promotes aquatic and riparian vegetation important for different dragonfly life stages, thus increasing their diversity. Additionally, we assume that this changes dragonfly species composition between restored and unrestored ponds. We surveyed exuviae in the riparian and aquatic vegetation along the shore of 29 (12 restored, 17 unrestored) man-made ponds in southwest Germany and assessed environmental variables known to affect dragonfly diversity. We identified the cover of tall sedges and submerged macrophytes as the driving biotic variables for dragonfly diversity and species composition, with restoration measures affecting submerged macrophyte cover directly but tall sedges indirectly via available sunlight. This study demonstrates that simple restoration measures not only have a positive effect on overall dragonfly diversity, but also increase habitat suitability for several species that would otherwise be absent. We therefore propose dragonflies as a suitable flagship group for pond conservation.     

Single-cell analysis reveals a novel uncultivated magnetotactic bacterium within the candidate division OP3

Magnetotactic bacteria (MTB) are a diverse group of prokaryotes that orient along magnetic fields using membrane-coated magnetic nanocrystals of magnetite (Fe(3) O(4) ) or greigite (Fe(3) S(4) ), the magnetosomes. Previous phylogenetic analysis of MTB has been limited to few cultivated species and most abundant members of natural populations, which were assigned to Proteobacteria and the Nitrospirae phyla. Here, we describe a single cell-based approach that allowed the targeted phylogenetic and ultrastructural analysis of the magnetotactic bacterium SKK-01, which was low abundant in sediments of Lake Chiemsee. Morphologically conspicuous single cells of SKK-01 were micromanipulated from magnetically collected multi-species MTB populations, which was followed by whole genome amplification and ultrastructural analysis of sorted cells. Besides intracellular sulphur inclusions, the large ovoid cells of SKK-01 harbour ～175 bullet-shaped magnetosomes arranged in multiple chains that consist of magnetite as revealed by TEM and EDX analysis. Sequence analysis of 16 and 23S rRNA genes from amplified genomic DNA as well as fluorescence in situ hybridization assigned SKK-01 to the candidate division OP3, which so far lacks any cultivated representatives. SKK-01 represents the first morphotype that can be assigned to the OP3 group as well as the first magnetotactic member of the PVC superphylum.     

Species diversity of magnetotactic bacteria from the Ol’khovka River, Russia

A fraction of magnetotactic bacteria was isolated by magnetic separation from the water and silt samples collected from the Ol’khovka River (Kislovodsk, Russia). A 16S rRNA clone library was obtained from the total DNA of the fraction by PCR amplification and molecular cloning. Phylogenetic analysis of 67 16S rRNA gene sequences of randomly selected clones demonstrated that two phylotypes of magnetotactic bacteria were present in the library: the first phylotype consisted of 42 sequences and the second one included only one sequence. The remaining 24 sequences belonged to non-magnetotactic bacteria. According to the results of phylogenetic analysis, both phylotypes were magnetotactic cocci; the predominant sequences were almost identical to the 16S rRNA sequence of the freshwater coccus TB24 (X81185.1) identified earlier among the magnetotactic bacteria isolated from Lake Chiemsee (Bavaria). The phylotype represented by a single sequence formed a separate branch in the dendrogram, with 97% similarity between its sequence and that of TB24. The discovered phylotypes formed with the sequences of uncultured freshwater magnetotactic cocci a separate branch within the class Alphaproteobacteria and presumably belonged to a separate family within the recently described order Magnetococcales. Despite the fact that phylogenetic analysis of the 16S rRNA clone library did not reveal any phylotypes of magnetotactic spirilla, after the secondary enrichment of the fraction of magnetotactic bacteria using the “race track” technique, a new strain of magnetotactic spirilla, Magnetospirillum SO-1, was isolated. The closest relative of strain SO-1 was the previously described magnetotactic spirillum Magnetospirillum magneticum AMB-1.     

Beaver population fluctuations and tropospheric methane emissions in boreal wetlands

Measurements of net methane flux were made during the 1988 ice-free season (May–October) at a beaver-meadow complex in northern Minnesota, USA. The site included upland boreal forest, sedge meadow, submerged aquatic plants, and the open water of a beaver pond. Annual fluxes were 8–11 g C/m² in the permanently wetted zones and 0.2–0.4 g C/m² at the occasionally inundated meadow and forest sites. These data, when coupled with long-term (46 yr) data on beaver (Castor canadensis) population size and habitat alteration, suggest that about 1% of the recent rise in atmospheric methane may be attributable to pond creation by beaver in North America.     

Freshwater plastispheres as a vector for foodborne bacteria and viruses

There is growing evidence that plastic particles can accumulate microorganisms that are pathogenic to humans or animals. In the current study, the composition of the plastispheres that accumulated on polypropylene (PP), polyvinyl chloride (PVC), and high-density polyethylene (HDPE) pieces submerged in a river in the southeast Norway was characterized by 16S rRNA amplicon sequencing. Seasonal and geographical effects on the bacterial composition of the plastisphere were identified, in addition to the detection of potential foodborne pathogenic bacteria and viruses as part of the plastisphere. The diversity and taxonomic composition of the plastispheres were influenced by the number of weeks in the river, the season, and the location. The bacterial diversity differed significantly in the plastisphere from June and September, with a generally higher diversity in June. Also, the community composition of the plastisphere was significantly influenced by the geographical location, while the type of plastic had less impact. Plastics submerged in river water assembled a variety of microorganisms including potentially pathogenic bacteria and viruses (noro- and adenovirus) detected by qPCR. Cultivation methods detected viable bacteria such as Escherichia coli and Listeria monocytogenes. The results highlight the need for additional research on the risk of contaminating food with plastic particles colonized with human pathogens through irrigation water.     

Characterization of Bacterial Magnetotactic Behaviors by Using a Magnetospectrophotometry Assay

Magnetotactic bacteria have the unique capacity of synthesizing intracellular single-domain magnetic particles called magnetosomes. The magnetosomes are usually organized in a chain that allows the bacteria to align and swim along geomagnetic field lines, a behavior called magnetotaxis. Two mechanisms of magnetotaxis have been described. Axial magnetotactic cells swim in both directions along magnetic field lines. In contrast, polar magnetotactic cells swim either parallel to the geomagnetic field lines toward the North Pole (north seeking) or antiparallel toward the South Pole (south seeking). In this study, we used a magnetospectrophotometry (MSP) assay to characterize both the axial magnetotaxis of “Magnetospirillum magneticum” strain AMB-1 and the polar magnetotaxis of magneto-ovoid strain MO-1. Two pairs of Helmholtz coils were mounted onto the cuvette holder of a common laboratory spectrophotometer to generate two mutually perpendicular homogeneous magnetic fields parallel or perpendicular to the light beam. The application of magnetic fields allowed measurements of the change in light scattering resulting from cell alignment in a magnetic field or in absorbance due to bacteria swimming across the light beam. Our results showed that MSP is a powerful tool for the determination of bacterial magnetism and the analysis of alignment and swimming of magnetotactic bacteria in magnetic fields. Moreover, this assay allowed us to characterize south-seeking derivatives and non-magnetosome-bearing strains obtained from north-seeking MO-1 cultures. Our results suggest that oxygen is a determinant factor that controls magnetotactic behavior.Magnetotactic bacteria are morphologically, metabolically, and phylogenetically diverse prokaryotes (1, 11). They synthesize unique intracellular organelles, the magnetosomes, which are single-domain magnetic crystals of the mineral magnetite or greigite enveloped by membranes. Magnetosomes are usually organized in a chain(s) within the cell and cause the cell to align along geomagnetic field lines while it swims. The highest numbers of magnetotactic bacteria are generally found at, or just below, the oxic-anoxic transition zone (OATZ) or redoxocline in aquatic habitats (1). Early studies showed that Northern Hemisphere magnetotactic bacteria swim preferentially northward in parallel with the geomagnetic field lines (north seeking [NS]) (2) and that those from the Southern Hemisphere swim preferentially antiparallel to the geomagnetic field lines to the magnetic South Pole (south seeking [SS]) (4). The geomagnetic field is inclined downward from horizontal in the Northern Hemisphere and upward in the Southern Hemisphere, with the inclination magnitude increasing from the equator to the poles. Therefore, magnetotaxis might guide cells in each hemisphere downward to less-oxygenated regions of aquatic habitats, where they would presumably stop swimming until conditions change (1). A recent study reported the coexistence of both NS and SS magnetotactic bacteria in the Northern Hemisphere, which conflicts with the prevalent model of the adaptive value of magnetotaxis (14).Under laboratory conditions, magnetotactic bacteria form microaerophilic bands of cells in oxygen-gradient medium. In fact, magnetotaxis and aerotaxis work together in these bacteria, and the behavior observed has been referred to as “magnetoaerotaxis.” Two different magnetoaerotactic mechanisms, termed polar and axial, are found in different bacterial species (6). The magnetotactic bacteria, principally the magnetotactic cocci, that swim persistently in one direction along the magnetic field (NS or SS) are polar magnetoaerotactic. Magnetotactic bacteria, especially the freshwater spirilla, that swim in either direction along the magnetic field lines with frequent, spontaneous reversals of swimming direction without turning around are axial magnetoaerotactic. For polar magnetotactic bacteria, the magnetic field provides an axis and a direction for motility, whereas for axial magnetotactic bacteria, the magnetic field provides only an axis of motility. The two mechanisms can best be seen in flattened capillary tubes containing suspensions of cells in reduced medium in a magnetic field oriented parallel to the capillary. An oxygen gradient forms along the tube, beginning at the ends of the capillary, with one oriented parallel and the other antiparallel to the magnetic field (1). Band formation by axial magnetoaerotactic cells, such as Magnetospirillum magnetotacticum cells, occurs at both ends of the capillary. Rotation of the magnetic field by 180° after the formation of the bands causes the cells in both bands to rotate 180°, but the bands remain intact. In contrast, band formation by polar magnetoaerotactic cells, such as the marine cocci, occurs only at the end of the capillary for which the magnetic field and the oxygen concentration gradient are oriented opposite to each other. Rotation of the magnetic field by 180° after the formation of the band causes the cells in the band to rotate 180° and swim away, resulting in the dispersal of the band (1). In this study, we developed a magnetospectrophotometry (MSP) assay that provides an alternative method for the quantitative and versatile characterization of the two magnetotactic mechanisms. Using this assay, we demonstrated the effect of artificial magnetic fields on the generation of homogeneous NS or SS magnetotactic bacterial populations.     

High diversity of <Emphasis Type="Italic">Ruppia</Emphasis> meadows in saline ponds and lakes of the western Mediterranean

Saline inland and coastal waterbodies are valuable habitats that deserve attention for the protection of their unique submerged macrophyte beds that render the water clear, stabilize sediments and provide a habitat for high biomasses of invertebrates as food for waterfowl. The ‘continental seagrass’ Ruppia has the widest salinity tolerance among the submerged macrophytes and occurs in a wide variety of saline saltmarsh pond and lagoon systems. Although two cosmopolitan species Ruppia maritima and Ruppia cirrhosa are recognized in Europe and Ruppia drepanensis in the western Mediterranean, their diversity and distribution are not well known. This previously held traditional idea that there are only two widespread Ruppia species suggests a uniform and very homogenized population structure following the hypothesis of long-distance-dispersal through strong bird-mediated dispersal events. Therefore, the Ruppia chloroplast DNA diversity was investigated along a more than 1,000 km transect of the Iberian Peninsula. We studied 492 individuals from 11 wetland areas (17 ponds) and sequenced a 1,753-bp length of seven chloroplast introns. Eight haplotypes represented at least four distinct groups or taxa which is higher than commonly accepted. Six wetland areas contained more than one haplotype and within-pond diversity occurred within distances as small as 30 m (5 out of 17 cases). This underlines the importance of single waterbodies for harbouring haplotypic diversity in Ruppia. Unique haplotypes were observed in four wetland areas and R. maritima was detected only from a low salinity pond, suggesting the species might be more rare than previously accepted. The present results tend to minimize an overall effect of strong bird-mediated dispersal. This emphasizes the role of regional pond habitat diversity for the preservation of Ruppia taxa and their unique haplotype diversity in extreme saline habitats. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008.     

Magnetosome magnetite biomineralization in a flagellated protist: evidence for an early evolutionary origin for magnetoreception in eukaryotes

The most well-recognized magnetoreception behaviour is that of the magnetotactic bacteria (MTB), which synthesize membrane-bounded magnetic nanocrystals called magnetosomes via a biologically controlled process. The magnetic minerals identified in prokaryotic magnetosomes are magnetite (Fe₃O₄) and greigite (Fe₃S₄). Magnetosome crystals, regardless of composition, have consistent, species-specific morphologies and single-domain size range. Because of these features, magnetosome magnetite crystals possess specific properties in comparison to abiotic, chemically synthesized magnetite. Despite numerous discoveries regarding MTB phylogeny over the last decades, this diversity is still considered underestimated. Characterization of magnetotactic microorganisms is important as it might provide insights into the origin and establishment of magnetoreception in general, including eukaryotes. Here, we describe the magnetotactic behaviour and characterize the magnetosomes from a flagellated protist using culture-independent methods. Results strongly suggest that, unlike previously described magnetotactic protists, this flagellate is capable of biomineralizing its own anisotropic magnetite magnetosomes, which are aligned in complex aggregations of multiple chains within the cell. This organism has a similar response to magnetic field inversions as MTB. Therefore, this eukaryotic species might represent an early origin of magnetoreception based on magnetite biomineralization. It should add to the definition of parameters and criteria to classify biogenic magnetite in the fossil record.     

Distribution, abundance, and genetic diversity of Clinostomum spp. metacercariae (Trematoda:Digenea) in a modified Ozark stream system

Land-use alterations can have profound influences on faunal distributions, including host-parasite relationships. Yellow grub trematodes ( Clinostomum spp.) have complex life cycles involving 3 hosts: a snail, a fish or amphibian, and a bird. Here, we analyze the distribution, prevalence, intensity, abundance, and genetic diversity of encysting metacercariae of Clinostomum spp. in salamanders and fishes throughout an aquatic system that includes a natural Ozark stream and man-made ponds. We found Clinostomum sp. infecting permanently aquatic Oklahoma salamanders ( Eurycea tynerensis ; 56% prevalence) and larval grotto salamanders ( Eurycea spelaea ) immediately downstream from a man-made pond. However, Clinostomum sp. did not infect any salamanders in the spring that supplies this pond, or in sections farther downstream (~0.5 and 2 km). Metacercariae of Clinostomum sp. were present in ~90% of introduced largemouth bass ( Micropterus salmoides ) in the man-made pond adjunct to the stream. Morphological examination and phylogenetic analyses based on the mitochondrial gene cytochrome oxidase 1 ( Co1 ) and the nuclear ribosomal gene 18S show that fishes and salamanders at this site are primarily infected with Clinostomum marginatum . There is a relatively high degree of mitochondrial haplotype diversity in C. marginatum at this site but no consistent genetic difference between parasites in largemouth bass from the man-made pond and those in salamanders from the stream. Based on the microgeographic distribution and relationships of metacercariae of C. marginatum at this site, we hypothesize that the adjunct man-made pond has created an ecological situation that brings the cercariae of this parasite into contact with novel stream salamander hosts.     

Diverse phylogeny and morphology of magnetite biomineralized by magnetotactic cocci

Magnetotactic bacteria (MTB) are diverse prokaryotes that produce magnetic nanocrystals within intracellular membranes (magnetosomes). Here, we present a large-scale analysis of diversity and magnetosome biomineralization in modern magnetotactic cocci, which are the most abundant MTB morphotypes in nature. Nineteen novel magnetotactic cocci species are identified phylogenetically and structurally at the single-cell level. Phylogenetic analysis demonstrates that the cocci cluster into an independent branch from other Alphaproteobacteria MTB, that is, within the Etaproteobacteria class in the Proteobacteria phylum. Statistical analysis reveals species-specific biomineralization of magnetosomal magnetite morphologies. This further confirms that magnetosome biomineralization is controlled strictly by the MTB cell and differs among species or strains. The post-mortem remains of MTB are often preserved as magnetofossils within sediments or sedimentary rocks, yet paleobiological and geological interpretation of their fossil record remains challenging. Our results indicate that magnetofossil morphology could be a promising proxy for retrieving paleobiological information about ancient MTB.