Study of Iron in Magnetotactic Bacteria

Bacteria have recently been discovered directing their movements by sensing the earth\u27s magnetic field. They contain arrays of crystals of lodestone or magnetite which they synthesize from iron in the ocean. The discovery of the same type of crystals in the abdomens of honey bees and the brains of homing pigeons suggests that nature is not oblivious to the earth\u27s magnetic field. The biological mechanism for sensing magnetic fields has never been determined. These bacteria are capable of biologically synthesizing highly purified single domain magnets that would be very expensive to produce chemically. The tiny perfect magnetite crystals made by the bacteria possibly could be utilized in microcircuitry. In addition, because these bacteria are attracted to metal surfaces surrounded by distortions in the earth\u27s magnetic field, they may play a role in ship fouling. The unique physical properties of the single domain ferromagnetic crystals of magnetite produced by these bacteria are being analyzed of heavy metal storage could be important in recovering metals from ore and nuclear wastes; this is a continuing research project supported by the Office of Naval Research

Shared Presence in Physician-Patient Communication: A Graphic Representation

Shared presence is a state of being in which physicians and patients enter into a deep sense of trust, respect, and knowing that facilitates healing. Communication between physicians and patients (and, in fact, all providers and recipients of health care) is the medium through which shared presence occurs, regardless of the presenting problem, time available, location of care, or clinical history of the patient. Conceptualizing how communication leads to shared presence has been a challenging task, however. Pathways of this process have been routinely lumped together as the biopsychosocial model or patient, person, and relationship-centered care—all deceptive in their simplicity but, in fact, highly complex—or reduced to descriptive explications of one constituent element (e.g., empathy). In this article, we reconcile these pathways and elements by presenting a graphic image for clinicians and teachers in medical education. This conceptual image serves as a framework to synthesize the vast literature on physician-patient communication. We place shared presence, the fundamental characteristic of effective clinical communication, at the center of our figure. Around this focal point, we locate four elemental factors that either contribute to or result from shared presence, including interpersonal skills, relational contexts, actions in clinical encounters, and healing outcomes. By visually presenting various known and emergent theories of physician-patient communication, outlining the flow of successful encounters between physicians and patients, and noting how such encounters can improve outcomes, physicians, other health care professionals, and medical educators can better grasp the complexity, richness, and potential for achieving shared presence with their patients

A Birefringence Relaxation Determination of Rotational Diffusion of Magnetotactic Bacteria

The orientational relaxation of the magnetotactic bacterium Aquaspirillum magnetotacticum is observed by the decay of the optical birefringence upon switching off an aligning magnetic field. The data yield a rotational diffusion constant Dr ≅ 0.13 s1 and information about cell sizes that is consistent with optical microscopy data

Hyperfine Interactions in Antiferromagnetic EuTe using the Te-125 Mossbauer Resonance

Europium telluride crystallizes in the NaCl structure and is antiferromagnetic with a Néel temperature TN of 9.6 K. We have used the 35.5 keV Møssbauer transition in Te-125 to examine the nature of the spontaneous magnetic moment which has been observed in conducting samples below TN. At 80 K the Mössbauer resonance spectrum consisted of a single absorption line comparable in width with the spectrum of nonmagnetic cubic ZnTe, indicating the absence of a significant quadrupole splitting at this temperature. At 4.2 K the line-width increased by a factor of 1.5, which is equivalent to a single magnetic hyperfine field at the Te sites of about 73 kOe. The line showed gradual broadening with increasing external longitudinal magnetic field up to 70 kOe at 4.2 K. These observations are consistent with the magnetization measurements as well as with recent spin-echo NMR experiments showing resonances which may be attributed to Te-125. We conclude from the shape of the Mössbauer line that the broadening observed at 4.2 K is most likely due to a single magnetic hyperfine field of magnitude 73 kOe acting at the Te sites. An applied magnetic field Hsite, but near the canted to paramagnetic transition (H≈66 kOe at 4.2 K) the observed hyperfine field increases more rapidly with H, reaching a value of 112 kOe when H=70 kOe

Magnetotaxis and Magnetic Particles in Bacteria

Magnetotactic bacteria contain magnetic particles that constitute a permanent magnetic dipole and cause each cell to orient and migrate along geomagnetic field lines. Recent results relevant to the biomineralization process and to the function of magnetotaxis are discussed

Inorganic Particles Produced by Microorganisms

The processes by which microorganisms, particularly bacteria, produce inorganic mineral particles are reviewed

Redox Reactivity of Bacterial and Mammalian Ferritin: Is Reductant Entry Into the Ferritin Interior a Necessary Step for Iron Release?

Both mammalian and bacterial ferritin undergo rapid reaction with small-molecule reductants, in the absence of Fe2+ chelators, to form ferritins with reduced (Fe2+) mineral cores. Large, low-potential reductants (flavoproteins and ferredoxins) similarly react anaerobically with both ferritin types to quantitatively produce Fe2+ in the ferritin cores. The oxidation of Fe2+ ferritin by large protein oxidants [cytochrome c and Cu(II) proteins] also occurs readily, yielding reduced heme and Cu(I) proteins and ferritins with Fe3+ in their cores. These latter oxidants also convert enthetically added Fe2+, bound in mammalian or bacterial apo- or holo-ferritin, to the corresponding Fe3+ state in the core of each ferritin type. Because the protein reductants and oxidants are much larger than the channels leading into the mineral core attached to the ferritin interior, we conclude that redox reactions involving the Fe2+/Fe3+\u3e components of the ferritin core can occur without direct interaction of the redox reagent at the mineral core surface. Our results also suggest that the oxo, hydroxy species of the core, composed essentially of Fe(O)OH, arise exclusively from solvent deprotonation. The long-distance ferritin-protein electron transfer observed in this study may occur by electron tunneling

Biomineralization of Magnetic Iron Minerals in Bacteria

Magnetotactic bacteria orient and migrate along magnetic field lines. This ability is based on a submicron assembly of single-magnetic domain iron mineral particles that elegantly solves the problem of how to construct a magnetic dipole that is large enough to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized cell. The solution is based on the ability of the bacteria to accumulate high concentrations of iron, and control the deposition, size and orientation of a specific iron mineral at specific locations in the cell

Effect of Magnetic Fields on Drug Induced Contractility and Mortality in Spirostomum

The influence of homogeneous magnetic fields up to 5.5 T on contractile frequency and mortality in the ciliate protozoan spirostomum ambiguum stimulated by 2,2′ PDS is reported. Magnetic fields are observed to decrease contractile frequency and to significantly increase mortality

Are There Magnetic Moments at the Transition Metal Sites in FeAl, CoAl, and NiAl?

Measurements of the hyperfine interactions in 57Fe in the CsCl structure intermetallic compounds FeAl, CoAl and NiAl are reported