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Tom Fenchel - One of the best experts on this subject based on the ideXlab platform.
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sulphur bacterium Thiovulum majus
2015Co-Authors: Tom FenchelAbstract:The swimming track of the sulphur/sulphide-oxidizing bacterium Thiovulum majus is a left-handed helix. The cells modulate swimming speed by changing the tangential speed andlor the pitch and radius of the helix. Whether attached (to a mucous thread) or swimming, the spherical cells rotate around their anterior-posterior axis in a counter-clockwise direction when observed from the posterior pole. Swimming speeds may exceed 600 pm s-l, which is 5-6 times faster than recorded for any other bacterium. Thiovulum cells congregate at oxygen tensions of about 4 % atmospheric saturation (085 kPa). Cells which accidentally leave the optimum zone make a U-turn within 150-200 pm, thus returning to where they came from. This represents a type of phobic response in which the eventual swimming direction is correlated with the initial direction; it is not a true chemotactic response in the sense that the cells can orient themselves in 0,-gradients. The 180"lbend of the swimming path is probably accomplished by changes in the rotational velocity component which take place when the cells swim into an adverse environment. The U-turn response allows the bacteria to maintain the characteristic 100-200 pm thick veils which separate the sulphidic and the oxygenated zone in or above sediments. Evidence for a chemosensory response to sulphide could not be found
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2005. Survey of motile microaerophilic bacterial morphotypes in the oxygen gradient above a marine sulfidic sediment
2015Co-Authors: Tom FenchelAbstract:Enrichment cultures for free-swimming microaerophilic bacteria were prepared from marine sulfidic sedi-ment samples (Nivå Bay, Denmark). We observed nine different morphotypes; three of these morphotypes represented already-described species, i.e., Thiovulum majus, “Candidatus Ovobacter propellens, ” and an as-yet-unnamed large vibrioid bacterium. In addition, we observed several morphotypes of spirilla and one vibrioid morphotype. A common feature of all investigated bacteria was that they aggregated chemotactically at the oxic-anoxic interface, whereas preferred oxygen concentration were in the range of 1 to 10 M. The motile behavior and flagellar dynamics are analyzed in detail with an emphasis on spirilla. Sulfidic marine sediments covered by air-saturated seawater are generally characterized by steep opposing oxygen and sul-fide gradients within the upper millimeters of the sediment. Dissolved sulfide is produced by sulfate-reducing bacteria within the anoxic deeper sediment layers, from where it con-stantly diffuses upward toward the sediment surface (23). The layer several 100 m in thickness where molecular oxygen and sulfide coexist at the oxic-anoxic interface harbors a variety of colorless sulfur bacteria, which are able to utilize the free energy obtained from the oxidation of reduced sulfur com-pounds (18, 25). The position of the oxic-anoxic interface often changes, e.g., due to convective water currents at the sediment surface or due to diel activity cycles of oxygenic photosynthesis (24). Thus, many colorless sulfur bacteria are highly motile in order to follow their preferred position within the oxygen gra-dient. If the oxic-anoxic interface is positioned within or directly at the surface of the sediment, species of colorless sulfur bacteria relying on surface associated motility are often abundant in high numbers (e.g., Beggiatoa spp. showing gliding motility o
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True chemotaxis in oxygen gradients of the sulfur-oxidizing bacterium Thiovulum majus.
Applied and environmental microbiology, 2001Co-Authors: Roland Thar, Tom FenchelAbstract:Observations of free-swimming Thiovulum majus cells show that these bacteria exhibit a phobic response as well as true chemotaxis in oxygen gradients. Both phenomena of their chemotactic behavior are integrated into a single model of helical klinotaxis, which is demonstrated by computer simulations.
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True chemotaxis in oxygen gradients of the sulfur-oxidizing bacterium Thiovulum majus
2001Co-Authors: Roland Thar, Tom FenchelAbstract:Observations of free-swimming Thiovulum majus cells show that these bacteria exhibit a phobic response as well as true chemotaxis in oxygen gradients. Both phenomena of their chemotactic behavior are integrated into a single model of helical klinotaxis, which is demonstrated by computer simulations. Many motile prokaryotes are able to accumulate in regions which are favorable for their physiological adaptations. In or-der to achieve this they have to sense physical parameters (e.g., light, magnetic fields, gravity, or concentrations of chemical substances) of their environment. If bacteria change their mo-tility patterns in response to chemical substances, this behavior is called chemotaxis. Following the terminology given by Dusenbery (9), chemotaxis can on principle be realized in two different ways. True taxis is given if responses to chemical gradients are directional, i.e., the moving direction of the or-ganism is correlated to the direction of the chemical gradient. If the responses are undirectional, the behavior is called
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motility and chemosensory behaviour of the sulphur bacterium Thiovulum majus
Microbiology, 1994Co-Authors: Tom FenchelAbstract:The swimming track of the sulphur/sulphide-oxidizing bacterium Thiovulum majus is a left-handed helix. The cells modulate swimming speed by changing the tangential speed and/or the pitch and radius of the helix. Whether attached (to a mucous thread) or swimming, the spherical cells rotate around their anterior-posterior axis in a counter-clockwise direction when observed from the posterior pole. Swimming speeds may exceed 600 μm s-1, which is 5-6 times faster than recorded for any other bacterium. Thiovulum cells congregate at oxygen tensions of about 4% atmospheric saturation (0.85 kPa). Cells which accidentally leave the optimum zone make a U-turn within 150-200 μm, thus returning to where they came from. This represents a type of phobic response in which the eventual swimming direction is correlated with the initial direction; it is not a true chemotactic response in the sense that the cells can orient themselves in O2-gradients. The 180°-bend of the swimming path is probably accomplished by changes in the rotational velocity component which take place when the cells swim into an adverse environment. The U-turn response allows the bacteria to maintain the characteristic 100-200 μm thick veils which separate the sulphidic and the oxygenated zone in or above sediments. Evidence for a chemosensory response to sulphide could not be found.
David M Karl - One of the best experts on this subject based on the ideXlab platform.
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phylogenetic diversity of the bacterial community from a microbial mat at an active hydrothermal vent system loihi seamount hawaii
Applied and Environmental Microbiology, 1995Co-Authors: Craig L Moyer, Fred C Dobbs, David M KarlAbstract:The phylogenetic diversity of small-subunit rRNA genes associated with the domain Bacteria was examined (by using previously defined operational taxonomic units [C. L. Moyer, F.C. Dobbs, and D. M. Karl, Appl. Environ. Microbiol. 60:871-879, 1994]; those for Pele's Vents Bacteria are hereafter abbreviated PVB OTUs) with samples from a microbial mat at an active, deep-sea hydrothermal vent system. A cluster of phylogenetically related PVB OTUs (OTUs 2, 3, 6, and 8) was closely affiliated with Thiovulum sp. contained within the epsilon subclass of the class Proteobacteria and accounted for 60.5% of the small-subunit rRNA bacterial clone library from Pele's Vents. A second, smaller cluster of PVB OTUs (OTUs 1 and 11) was closely affiliated with Xanthomonas sp., contained within the gamma subclass of the Proteobacteria and accounted for a total of 27.1% of the bacterial clone library. The remaining five PVB OTUs each accounted for 2.1% of the clones recovered and were affiliated with the following phylogenetic groups: PVB OTU 5 was a member of the Alteromonas group; PVB OTU 12 was a member of the Colwellia assemblage; PVB OTU 4 was loosely determined to be a member of the Thiothrix group, with the endosymbiotic bacteria from Bathymodiolus thermophilus and Calyptogena magnifica as the nearest relatives; PVB OTU 10B was a member of the Myxobacterium group; and PVB OTU 9A was a member of the Paraphyletic assemblage, with the Octopus Spring microbial mat type K clone as the closest known relative.(ABSTRACT TRUNCATED AT 250 WORDS)
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Phylogenetic Diversity of the Bacterial Community from a Microbial Mat at an Active, Hydrothermal Vent System,
1994Co-Authors: Loihi Seamount Hawaii, Craig L Moyer, Fred C Dobbs, David M KarlAbstract:The phylogenetic diversity of small-subunit rRNA genes associated with the domain Bacteria was examined (by using previously defined operational taxonomic units [C. L. Moyer, F. C. Dobbs, and D. M. Karl, Appl. Environ. Microbiol. 60:871–879, 1994]; those for Pele’s Vents Bacteria are hereafter abbreviated PVB OTUs) with samples from a microbial mat at an active, deep-sea hydrothermal vent system. A cluster of phylogenetically related PVB OTUs (OTUs 2, 3, 6, and 8) was closely affiliated with Thiovulum sp. contained within the � subclass of the class Proteobacteria and accounted for 60.5 % of the small-subunit rRNA bacterial clone library from Pele’s Vents. A second, smaller cluster of PVB OTUs (OTUs 1 and 11) was closely affiliated with Xanthomonas sp., contained within the � subclass of the Proteobacteria and accounted for a total of 27.1 % of the bacterial clone library. The remaining five PVB OTUs each accounted for 2.1 % of the clones recovered and were affiliated with the following phylogenetic groups: PVB OTU 5 was a member of the Alteromonas group; PVB OTU 12 was a member of the Colwellia assemblage; PVB OTU 4 was loosely determined to be a member of the Thiothrix group, with the endosymbiotic bacteria from Bathymodiolus thermophilus and Calyptogena magnifica as the nearest relatives; PVB OTU 10B was a member of the Myxobacterium group; and PVB OTU 9A was a member of the Paraphyletic assemblage, with the Octopus Spring microbial mat type K clone as the closest known relative. PVB OTU 7 was determined to be a PCR-generated chimeric structure combined from tw
Albert Libchaber - One of the best experts on this subject based on the ideXlab platform.
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nucleation of rotating crystals by Thiovulum majus bacteria
New Journal of Physics, 2018Co-Authors: Alexander P Petroff, Albert LibchaberAbstract:Thiovulum majus self-organize on glass surfaces into active two-dimensional crystals of rotating cells. Unlike classical crystals, these bacterial crystallites continuously rotate and reorganize as the power of rotating cells is dissipated by the surrounding flow. In this article, we describe the earliest stage of crystallization, the attraction of two bacteria into a hydrodynamically-bound dimer. This process occurs in three steps. First a free-swimming cell collides with the wall and becomes hydrodynamically bound to the two-dimensional surface. We present a simple model to understand how viscous forces localize cells near the chamber walls. Next, the cell diffuses over the surface for an average of s before escaping to the bulk fluid. The diffusion coefficient of these diameter cells corresponds to a temperature of K, and thus cannot be explained by equilibrium fluctuations. Finally, two cells coalesce into a rotating dimer when the convergent flow created by each cell overwhelms their active Brownian motion. This occurs when cells diffuse to within a distance of 13.3 ± 0.2 μm of each other.
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hydrodynamics and collective behavior of the tethered bacterium Thiovulum majus
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Alexander P Petroff, Albert LibchaberAbstract:The ecology and dynamics of many microbial systems, particularly in mats and soils, are shaped by how bacteria respond to evolving nutrient gradients and microenvironments. Here we show how the response of the sulfur-oxidizing bacterium Thiovulum majus to changing oxygen gradients causes cells to organize into large-scale fronts. To study this phenomenon, we develop a technique to isolate and enrich these bacteria from the environment. Using this enrichment culture, we observe the formation and dynamics of T. majus fronts in oxygen gradients. We show that these dynamics can be understood as occurring in two steps. First, chemotactic cells moving up the oxygen gradient form a front that propagates with constant velocity. We then show, through observation and mathematical analysis, that this front becomes unstable to changes in cell density. Random perturbations in cell density create oxygen gradients. The response of cells magnifies these gradients and leads to the formation of millimeter-scale fluid flows that actively pull oxygenated water through the front. We argue that this flow results from a nonlinear instability excited by stochastic fluctuations in the density of cells. Finally, we show that the dynamics by which these modes interact can be understood from the chemotactic response of cells. These results provide a mathematically tractable example of how collective phenomena in ecological systems can arise from the individual response of cells to a shared resource.
Alexander P Petroff - One of the best experts on this subject based on the ideXlab platform.
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nucleation of rotating crystals by Thiovulum majus bacteria
New Journal of Physics, 2018Co-Authors: Alexander P Petroff, Albert LibchaberAbstract:Thiovulum majus self-organize on glass surfaces into active two-dimensional crystals of rotating cells. Unlike classical crystals, these bacterial crystallites continuously rotate and reorganize as the power of rotating cells is dissipated by the surrounding flow. In this article, we describe the earliest stage of crystallization, the attraction of two bacteria into a hydrodynamically-bound dimer. This process occurs in three steps. First a free-swimming cell collides with the wall and becomes hydrodynamically bound to the two-dimensional surface. We present a simple model to understand how viscous forces localize cells near the chamber walls. Next, the cell diffuses over the surface for an average of s before escaping to the bulk fluid. The diffusion coefficient of these diameter cells corresponds to a temperature of K, and thus cannot be explained by equilibrium fluctuations. Finally, two cells coalesce into a rotating dimer when the convergent flow created by each cell overwhelms their active Brownian motion. This occurs when cells diffuse to within a distance of 13.3 ± 0.2 μm of each other.
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hydrodynamics and collective behavior of the tethered bacterium Thiovulum majus
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Alexander P Petroff, Albert LibchaberAbstract:The ecology and dynamics of many microbial systems, particularly in mats and soils, are shaped by how bacteria respond to evolving nutrient gradients and microenvironments. Here we show how the response of the sulfur-oxidizing bacterium Thiovulum majus to changing oxygen gradients causes cells to organize into large-scale fronts. To study this phenomenon, we develop a technique to isolate and enrich these bacteria from the environment. Using this enrichment culture, we observe the formation and dynamics of T. majus fronts in oxygen gradients. We show that these dynamics can be understood as occurring in two steps. First, chemotactic cells moving up the oxygen gradient form a front that propagates with constant velocity. We then show, through observation and mathematical analysis, that this front becomes unstable to changes in cell density. Random perturbations in cell density create oxygen gradients. The response of cells magnifies these gradients and leads to the formation of millimeter-scale fluid flows that actively pull oxygenated water through the front. We argue that this flow results from a nonlinear instability excited by stochastic fluctuations in the density of cells. Finally, we show that the dynamics by which these modes interact can be understood from the chemotactic response of cells. These results provide a mathematically tractable example of how collective phenomena in ecological systems can arise from the individual response of cells to a shared resource.
Craig L Moyer - One of the best experts on this subject based on the ideXlab platform.
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phylogenetic diversity of the bacterial community from a microbial mat at an active hydrothermal vent system loihi seamount hawaii
Applied and Environmental Microbiology, 1995Co-Authors: Craig L Moyer, Fred C Dobbs, David M KarlAbstract:The phylogenetic diversity of small-subunit rRNA genes associated with the domain Bacteria was examined (by using previously defined operational taxonomic units [C. L. Moyer, F.C. Dobbs, and D. M. Karl, Appl. Environ. Microbiol. 60:871-879, 1994]; those for Pele's Vents Bacteria are hereafter abbreviated PVB OTUs) with samples from a microbial mat at an active, deep-sea hydrothermal vent system. A cluster of phylogenetically related PVB OTUs (OTUs 2, 3, 6, and 8) was closely affiliated with Thiovulum sp. contained within the epsilon subclass of the class Proteobacteria and accounted for 60.5% of the small-subunit rRNA bacterial clone library from Pele's Vents. A second, smaller cluster of PVB OTUs (OTUs 1 and 11) was closely affiliated with Xanthomonas sp., contained within the gamma subclass of the Proteobacteria and accounted for a total of 27.1% of the bacterial clone library. The remaining five PVB OTUs each accounted for 2.1% of the clones recovered and were affiliated with the following phylogenetic groups: PVB OTU 5 was a member of the Alteromonas group; PVB OTU 12 was a member of the Colwellia assemblage; PVB OTU 4 was loosely determined to be a member of the Thiothrix group, with the endosymbiotic bacteria from Bathymodiolus thermophilus and Calyptogena magnifica as the nearest relatives; PVB OTU 10B was a member of the Myxobacterium group; and PVB OTU 9A was a member of the Paraphyletic assemblage, with the Octopus Spring microbial mat type K clone as the closest known relative.(ABSTRACT TRUNCATED AT 250 WORDS)
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Phylogenetic Diversity of the Bacterial Community from a Microbial Mat at an Active, Hydrothermal Vent System,
1994Co-Authors: Loihi Seamount Hawaii, Craig L Moyer, Fred C Dobbs, David M KarlAbstract:The phylogenetic diversity of small-subunit rRNA genes associated with the domain Bacteria was examined (by using previously defined operational taxonomic units [C. L. Moyer, F. C. Dobbs, and D. M. Karl, Appl. Environ. Microbiol. 60:871–879, 1994]; those for Pele’s Vents Bacteria are hereafter abbreviated PVB OTUs) with samples from a microbial mat at an active, deep-sea hydrothermal vent system. A cluster of phylogenetically related PVB OTUs (OTUs 2, 3, 6, and 8) was closely affiliated with Thiovulum sp. contained within the � subclass of the class Proteobacteria and accounted for 60.5 % of the small-subunit rRNA bacterial clone library from Pele’s Vents. A second, smaller cluster of PVB OTUs (OTUs 1 and 11) was closely affiliated with Xanthomonas sp., contained within the � subclass of the Proteobacteria and accounted for a total of 27.1 % of the bacterial clone library. The remaining five PVB OTUs each accounted for 2.1 % of the clones recovered and were affiliated with the following phylogenetic groups: PVB OTU 5 was a member of the Alteromonas group; PVB OTU 12 was a member of the Colwellia assemblage; PVB OTU 4 was loosely determined to be a member of the Thiothrix group, with the endosymbiotic bacteria from Bathymodiolus thermophilus and Calyptogena magnifica as the nearest relatives; PVB OTU 10B was a member of the Myxobacterium group; and PVB OTU 9A was a member of the Paraphyletic assemblage, with the Octopus Spring microbial mat type K clone as the closest known relative. PVB OTU 7 was determined to be a PCR-generated chimeric structure combined from tw