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NASA NTRS1986

Exercise Responses after Inactivity

The exercise response after bed rest inactivity is a reduction in the physical work capacity and is manifested by significant decreases in oxygen uptake. The magnitude of decrease in maximal oxygen intake V(dot)O2max is related to the duration of confinement and the pre-bed-rest level of aerobic fitness; these relationships are relatively independent of age and gender. The reduced exercise performance and V(dot)O2max following bed rest are associated with various physiological adaptations including reductions in blood volume, submaximal and maximal stroke volume, maximal cardiac output, sceletal muscle tone and strength, and aerobic enzyme capacities, as well as increases in venous compliance and submaximal and maximal heart rate. This reduction in physiological capacity can be partially restored by specific countermeasures that provide regular muscular activity or orhtostatic stress or both during the bed rest exposure. The understanding of these physiological and physical responses to exercise following bed rest inactivity has important implications for the solution to safety and health problems that arise in clinical medicine, aerospace medicine, sedentary living, and aging.

Convertino, Victor A.↗

NASA NTRS1992

STS-47 Mission Highlights Resource Tape

The mission of the STS-47 flight is highlighted in this video. The flight crew consisted of: Cmdr. 'Hoot' Gibson, Pilot Kurt Brown, Payload Cmdr. Jan Davis, Payload Specialist. M. Mohri (Japanese Astronaut), and Mission Specialists Jay Apt and May Jemison. The primary goal of this mission was the set-up and carrying out of experiments in the accompanying Japanese Spacelab (SL-J) in cooperation with the Japanese Space Program. Dr. Mohri is the first professional Japanese astronaut to fly in space. Vice President Dan Quayle and his wife are shown addressing the astronauts of the Space Shuttle Endeavour with a small pre-launch speech. On this flight many different physical, physiological, and biological spaceborne experiments were performed. These experiments included: a gas evaporation in low gravity environment experiment; a brainwave signals from carp experiment; several human eye movement and visual physiological tests; various physiological tests on a variety of insects and frogs; a embryology experiments on tadpoles; several experiments concerned with fluid dynamics; an imaging furnace test with heated glass containing gold particles (flow measurement); a Solid Surface Combustion Experiment; and a protein crystal growth experiment. Launch, in-orbit, and landing footage is shown, along with a variety of crew activities. One feature that astronauts were able to videotape was the actual in-orbit movement of the side wing flaps of the Space Shuttle.

Source record↗

NASA NTRS1996

Effect of +Gz Acceleration on the Oxygen Uptake-Excercise Load Relationship during Lower Extremity Ergometer Excercise

Long term spaceflight and habitation of a space station and/or the moon require that astronauts be provided with sufficient environmental and physiological support so that they can not only function in microgravity but be returned to earth safely. As the duration of habitation in microgravity increase the effects of the concomitant deconditioning of body systems becomes a concern for added exercise in space and for reentry to Earth gravity. Many countermeasures have been proposed to maintain proper functioning of the body, but none have proved sufficient, especially when the cost of crew time spent in these activities is considered. The issue of appropriate countermeasures remains unresolved. Spaceflight deconditioning decreases tolerance to +Gz acceleration, head to foot, the direction which is experienced during reentry; the result is that the crew member is more prone to becoming pre-syncopal or syncopal, thus exacerbating the orthostatic intolerance. All ground-based research using microgravity analogues has produced this same lowered G tolerance. When intermittent exposure to +1 to +4 Gz acceleration training was used, some alleviation of orthosatic intolerance and negative physiological effects of deconditioning occurred. Exercise alone was not as effective; but the added G force was. The physiological responses to acceleration added to exercise training have not been clearly shown. We will test the hypothesis that there will be no difference in the exercise oxygen uptake-exercise load relationship with added +Gz acceleration. We wi also compare oxygen uptake during graded exercise-acceleration loads in the human-powered short arm centrifuge with those from normal supine exercise loads. The human-powered short arm centrifuge was built by NASA engineers at Ames Research Center.

Jackson, Catherine G. R.↗

NASA NTRS1991

High-Moisture Diet for Laboratory Rats: Complete Blood Counts, Serum Biochemical Values, and Intestinal Enzyme Activity

Rats were fed an irradiated high-moisture diet (KSC-25) with or without access to a water bottle. Physiologic values were compared between these two groups and a group of rats fed a purified diet. Hematologic and serum biochemical values, urine specific gravity, and intestinal enzyme activities were determined from samples collected from the three groups of rats. Sprague Dawley rats (n=32) fed the irradiated high-moisture diet with or without a water bottle were the test animals. Rats (n=16) fed an irradiated purified diet and water provided via a water bottle were the control group. The purified diet formulation, modified AIN-76A, is a commonly used purified diet for laboratory rodents. All rats remained alert and healthy throughout the study. A comparison of the physiologic values of rats in this study with reported normal values indicated that all of the rats in the study were in good health. Significant differences (P less than 0.05) of the physiologic values from each rat group are reported.

Battles, August H.↗

NASA NTRS1997

Predicting Photosynthetic Fluxes from Spectral Reflectance of Leaves and Canopies

The central hypothesis of this study has been that photosynthetic efficiency and capacity can be predicted from 'physiological reflectance indices' derived from spectral reflectance of leaves and canopies. I have approached this topic with a combination of laboratory and field experiments, and have also explored the potential of deriving a meaningful physiological index from imaging spectrometry (e.g. AVIRIS). A few highlights are presented below. The main emphasis has been on the 'Photochemical Reflectance Index' (PRI), derived from reflectance at 531 nm and 570 nm. Unlike most 'conventional' vegetation indices (e.g. NDVI), PRI changes rapidly both with illumination and physiological state, because it detects the interconversion of xanthophyll cycle pigments, which serve as photoregulatory pigments and control energy distribution for the photosynthetic system. This approach has differed dramatically from most remote sensing in that it has emphasized temporal variation in narrow-band spectral signatures, instead of spatial patterns of broadband indices. Our primary conclusion has been that PRI works well as an index of photosynthetic light-use efficiency at the leaf scale, much in the same way as the fluorescence index DeltaF/Fm. However, unlike DeltaF/Fm which must be measured at close scales, PRI can be sampled at a range of spatial scales, presenting the possibility of monitoring photosynthetic fluxes remotely.

Gamon, John A.↗

NASA NTRS1998

An Evaluation of the Frequency and Severity of Motion Sickness Incidences in Personnel Within the Command and Control Vehicle (C2V)

The purpose of this study was to assess the frequency and severity of motion sickness in personnel during a field exercise in the Command and Control Vehicle (C2V). This vehicle contains four workstations where military personnel are expected to perform command decisions in the field during combat conditions. Eight active duty military men (U.S. Army) at the Yuma Proving Grounds in Arizona participated in this study. All subjects were given baseline performance tests while their physiological responses were monitored on the first day. On the second day of their participation, subjects rode in the C2V while their physiological responses and performance measures were recorded. Self-reports of motion sickness were also recorded. Results showed that only one subject experienced two incidences of emesis. However, seven out of the eight subjects reported other motion sickness symptoms; most predominant was the report of drowsiness, which occurred a total of 19 times. Changes in physiological responses were observed relative to motion sickness symptoms reported and the different environmental conditions (i.e., level, hills, gravel) during the field exercise. Performance data showed an overall decrement during the C2V exercise. These findings suggest that malaise and severe drowsiness can potentially impact the operational efficiency of the C2V crew. It was concluded that conflicting sensory information from the subject's visual displays and movements of the vehicle during the field exercise significantly contributed to motion sickness symptoms. It was recommended that a second study be conducted to further evaluate the impact of seat position or orientation and C2V experience on motion sickness susceptibility. Further, it was recommended that an investigation be performed on behavioral methods for improving crew alertness, motivation, and performance and for reducing malaise.

Cowings, Patricia S.↗

NASA NTRS1999

Crew Factors in Flight Operations X: Alertness Management in Flight Operations

In response to a 1980 congressional request, NASA Ames Research Center initiated a Fatigue/Jet Lag Program to examine fatigue, sleep loss, and circadian disruption in aviation. Research has examined fatigue in a variety of flight environments using a range of measures (from self-report to performance to physiological). In 1991, the program evolved into the Fatigue Countermeasures Program, emphasizing the development and evaluation of strategies to maintain alertness and performance in operational settings. Over the years, the Federal Aviation Administration (FAA) has become a collaborative partner in support of fatigue research and other Program activities. From the inception of the Program, a principal goal was to return the information learned from research and other Program activities to the operational community. The objectives of this Education and Training Module are to explain what has been learned about the physiological mechanisms that underlie fatigue, demonstrate the application of this information in flight operations, and offer some specific fatigue counter-measure recommendations. It is intended for all segments of the aeronautics industry, including pilots, flight attendants, managers, schedulers, safety and policy personnel, maintenance crews, and others involved in an operational environment that challenges human physiological capabilities because of fatigue, sleep loss, and circadian disruption.

Rosekind, Mark R.↗

NASA NTRS1999

Monitoring and Correcting Autonomic Function Aboard Mir: NASA Technology Used in Space and on Earth to Facilitate Adaptation

The broad objective of the research was to study individual characteristics of human adaptation to long duration spaceflight and possibilities of their correction using autonomic conditioning. The changes in autonomic state during adaptation to microgravity can have profound effects on the operational efficiency of crewmembers and may result in debilitating biomedical symptoms. Ground-based and inflight experiment results showed that certain responses of autonomic nervous system were correlated with, or consistently preceded, reports of performance decrements or the symptoms. Autogenic-Feedback-Training Exercise (AFTE) is a physiological conditioning method that has been used to train people to voluntary control several of their own physiological responses. The specific objectives were: 1) To study human autonomic nervous system (ANS) responses to sustained exposure to microgravity; 2) To study human behavior/performance changes related to physiology; 3) To evaluate the effectiveness of preflight autonomic conditioning (AFTE) for facilitating adaptation to space and readaptation to Earth; and 4) To archive these data for the NASA Life Sciences Data Archive and thereby make this information available to the international scientific community.

Cowings, P.↗

NASA NTRS1999

Carotid Baroreflex Function During Prolonged Exercise

Astronauts are often required to work (exercise) at moderate to high intensities for extended periods while performing extra-vehicular activities (EVA). Although the physiologic responses associated with prolonged exercise have been documented, the mechanisms involved in blood pressure regulation under these conditions have not yet been fully elucidated. An understanding of this issue is pertinent to the ability of humans to perform work in microgravity and complies with the emphasis of NASA's Space Physiology and Countermeasures Program. Prolonged exercise at a constant workload is know to result in a progressive decrease in mean arterial pressure (MAP) concomitant with a decrease in stroke volume and a compensatory increase in heart rate. The continuous decrease in MAP during the exercise, which is related to the thermoregulatory redistribution of circulating blood volume to the cutaneous circulation, raises the question as to whether there is a loss of baroreflex regulation of arterial blood pressure. We propose that with prolongation of the exercise to 60 minutes, progressive increases on central command reflect a progressive upward resetting of the carotid baroreflex (CBR) such that the operating point of the CBR is shifted to a pressure below the threshold of the reflex rendering it ineffectual in correcting the downward drift in MAP. In order to test this hypothesis, experiments have been designed to uncouple the global hemodynamic response to prolonged exercise from the central command mediated response via: (1) continuous maintenance of cardiac filling volume by intravenous infusion of a dextran solution; and (2) whole body surface cooling to counteract thermoregulatory cutaneous vasodialation. As the type of work (exercise) performed by astronauts is inherently arm and upper body dependent, we will also examine the physiologic responses to prolonged leg cycling and arm ergometry exercise in the supine positions with and without level lower body negative pressure (-10 torr) to mimic spaceflight- related decreases in cardiac filling volumes.

Raven, P. B.↗

NASA NTRS1999

BRN 3.1 Knockouts Affect the Vestibular, Autonomic, and Circadian Rhythm Responses to 2G Exposure

Our previous studies have demonstrated that 2G exposure via centrifugation significantly attenuated the daily mean and circadian rhythm amplitude of rat body temperature (Tb), heart rate, and activity (Act). In addition, 2G exposure activates neural responses in several vestibular, autonomic, and circadian nuclei. Although we have characterized the effect of 2G on an animal's physiological, neuronal, and behavioral responses, it will be important to understand the underlying neural and physiological mechanisms that mediate those responses. For example, the vestibular responses, proprioceptive feedback, or fluid shifts may be the critical factors that mediate the responses to 2G. As a first step to understand the relative importance of these different response pathways to altered gravitational fields, this study examined the contribution of the vestibular system by utilizing an animal model from molecular biology. Brain 3.1 (Bm 3.1) is a POU domain homeobox gene involved in the normal development of the vestibular and auditory system. Brn 3.1 deletion results in a loss of hair cells in the otoliths, semicircular canals, and cochlea. As a result mice with a Brn 3.1 deletion do not have a functioning vestibular or auditory system. The BRN 3.1 knockout mouse could be a very useful animal model for isolating the role of the vestibular system in mediating the physiological responses to 2G exposure. Therefore, this study compared the effect of 2G exposure via centrifugation between Brn 3.1 knockout (KO) versus Wildtype (W) mice.

Murakami, D. M.↗

NASA NTRS1999

Instrumentation for Non-Invasive Assessment of Cardiovascular Regulation

It is critically important to be able to assess alterations in cardiovascular regulation during and after space flight. We propose to develop an instrument for the non-invasive assessment of such alterations that can be used on the ground and potentially during space flight. This instrumentation would be used by the Cardiovascular Alterations Team at multiple sites for the study of the effects of space flight on the cardiovascular system and the evaluation of countermeasures. In particular, the Cardiovascular Alterations Team will use this instrumentation in conjunction with ground-based human bed-rest studies and during application of acute stresses e.g., tilt, lower body negative pressure, and exercise. In future studies, the Cardiovascular Alterations Team anticipates using this instrumentation to study astronauts before and after space flight and ultimately, during space flight. The instrumentation may also be used by the Bone Demineralization/Calcium Metabolism Team, the Neurovestibular Team and the Human Performance Factors, Sleep and Chronobiology Team to measure changes in autonomic nervous function. The instrumentation will be based on a powerful new technology - cardiovascular system identification (CSI) - which has been developed in our laboratory. CSI provides a non-invasive approach for the study of alterations in cardiovascular regulation. This approach involves the analysis of second-to-second fluctuations in physiologic signals such as heart rate and non-invasively measured arterial blood pressure in order to characterize quantitatively the physiologic mechanisms responsible for the couplings between these signals. Through the characterization of multiple physiologic mechanisms, CSI provides a closed-loop model of the cardiovascular regulatory state in an individual subject.

Cohen, Richard J.↗

NASA NTRS1981

Variation Principles and Applications in the Study of Cell Structure and Aging

In this report we have attempted to show that "some reality lies concealed in biological variation". This "reality" has its principles, laws, mechanisms, and rules, only a few of which we have sketched. A related idea we pursued was that important information may be lost in the process of ignoring frequency distributions of physiological variables (as is customary in experimental physiology and gerontology). We suggested that it may be advantageous to expand one's "statistical field of vision" beyond simple averages +/- standard deviations. Indeed, frequency distribution analysis may make visible some hidden information not evident from a simple qualitative analysis, particularly when the effect of some external factor or condition (e.g., aging, dietary chemicals) is being investigated. This was clearly illustrated by the application of distribution analysis in the study of variation in mouse liver cellular and fine structure, and may be true of fine structural studies in general. In living systems, structure and function interact in a dynamic way; they are "inseparable," unlike in technological systems or machines. Changes in fine structure therefore reflect changes in function. If such changes do not exceed a certain physiologic range, a quantitative analysis of structure will provide valuable information on quantitative changes in function that may not be possible or easy to measure directly. Because there is a large inherent variation in fine structure of cells in a given organ of an individual and among individuals, changes in fine structure can be analyzed only by studying frequency distribution curves of various structural characteristics (dimensions). Simple averages +/- S.D. do not in general reveal all information on the effect of a certain factor, because often this effect is not uniform; on the contrary, this will be apparent from distribution analysis because the form of the curves will be affected. We have also attempted to show in this chapter that similar general statistical principles and mechanisms may be operative in biological and technological systems. Despite the common belief that most biological and technological characteristics of interest have a symmetric bell-shaped (normal or Gaussian) distribution, we have shown that more often than not, distributions tend to be asymmetric and often resemble a so-called log-normal distribution. We saw that at least three general mechanisms may be operative, i.e., nonadditivity of influencing factors, competition among individuals for a common resource, and existence of an "optimum" value for a studied characteristic; more such mechanisms could exist.

Economos, Angelos C.↗

NASA NTRS1995

Exercise and Human Immunodeficiency Virus (HIV-1) Infection

The human immune system is highly efficient and remarkably protective when functioning properly. Similar to other physiological systems, it functions best when the body is maintained with a balanced diet, sufficient rest and a moderately stress-free lifestyle. It can be disrupted by inappropriate drug use and extreme emotion or exertion. The functioning of normal or compromised immune systems can be enhanced by properly prescribed moderate exercise conditioning regimens in healthy people, and in some human immunodeficiency virus (HIV-1)-infected patients but not in others who unable to complete an interval training program. Regular exercise conditioning in healthy people reduces cardiovascular risk factors, increases stamina, facilitates bodyweight control, and reduces stress by engendering positive feelings of well-being. Certain types of cancer may also be suppressed by appropriate exercise conditioning. Various exercise regimens are being evaluated as adjunct treatments for medicated patients with the HIV-1 syndrome. Limited anecdotal evidence from patients suggests that moderate exercise conditioning is per se responsible for their survival well beyond expectancy. HIV-1-infected patients respond positively, both physiologically and psychologically, to moderate exercise conditioning. However, the effectiveness of any exercise treatment programme depends on its mode, frequency, intensity and duration when prescribed o complement the pathological condition of the patient. The effectiveness of exercise conditioning regimens in patients with HIV-1 infection is reviewed in this article. In addition, we discuss mechanisms and pathways, involving the interplay of psychological and physiological factors, through which the suppressed immune system can be enhanced. The immune modulators discussed are endogenous opioids, cytokines, neurotransmitters and other hormones. Exercise conditioning treatment appears to be more effective when combined with other stress management procedures.

Lawless, DeSales↗

NASA NTRS1998

Diurnal Reflectance Changes in Vegetation Observed with AVIRIS

Among the most important short-term dynamic biological processes are diurnal changes in canopy water relations. Plant regulation of water transport through stomatal openings affects other gaseous transport processes, often dramatically decreasing photosynthetic fixation of carbon dioxide during periods of water stress. Water stress reduces stomatal conductance of water vapor through the leaf surface and alters the diurnal timing of stomatal opening. Under non-water stressed conditions, stomates typically open soon after dawn and transpire water vapor throughout the daylight period. During stress periods, stomates may close for part of the day, generally near mid-day. Under prolonged stress conditions, stomatal closure shifts to earlier times during the day; stomates may close by mid-morning and remain closed until the following morning - or remain closed entirely. Under these conditions the relationship between canopy greenness (e.g., measured with a vegetation index or by spectral mixture analysis) and photosynthetic fixation of carbon is lost and the remotely sensed vegetation metric is a poor predictor of gas exchange. Prediction of stomatal regulation and exchange of water and trace gases is critical for ecosystem and climate models to correctly estimate budgets of these gases and understand or predict other processes like gross and net ecosystem primary production. Plant gas exchange has been extensively studied by physiologists at the leaf and whole plant level and by biometeorologists at somewhat larger scales. While these energy driven processes follow a predictable if somewhat asymmetric diurnal cycle dependent on soil water availability and the constraints imposed by the solar energy budget, they are nonetheless difficult to measure at the tree and stand levels using conventional methods. Ecologists have long been interested in the potential of remote sensing for monitoring physiological changes using multi-temporal images. Much of this research has focused on day-to-day changes in water use, especially for agricultural applications. Ustin et al. showed seasonal changes in canopy water content in chaparral shrub could be estimated using optical methods. Vanderbilt et al. followed asymmetric diurnal changes in the reflectance of a walnut orchard, but could not attribute specific reflectance changes to specific changes in canopy architecture or physiology. Forests and shrub lands in California experience prolonged periods of drought, sometimes extending six months without precipitation. The conifer and evergreen chaparral communities common to the foothill region around the central valley of California retain their foliage throughout the summer and have low transpiration rates despite high net radiation and temperature conditions. In contrast, grasslands and drought resistant deciduous species in the same habitat are seasonally dormant in summer. Because of differences in the mechanisms of drought tolerance, rooting depth and physiology between different plant communities in the region, it is likely that they display differences in diurnal water relations. The presence of diverse plant communities provides an opportunity to investigate possible diurnal landscape patterns in water relations that could be observed by an airborne hyperspectral scanner. This investigation of AVIRIS data collected over forest and shrub land represents the continuation of a prior investigation involving spectral mixture analysis of diurnal effects in the same AVIRIS data set.

Vanderbilt, V. C.↗

NASA NTRS2000

NASA Space Technology Can Improve Soldier Health, Performance and Safety

One of the primary goals of NASA Life Sciences research is '... to enable a permanent human presence in space.' To meet this goal, NASA is creating alternative protocols designed to evaluate and test countermeasures that will account for and correct the environmental effects of space flight on crewmembers health, safety, and operational performance. NASA investigators have previously evaluated the effects of long-duration space flight on physiology and performance of cosmonauts aboard the MIR space station. They also initiated tests of a countermeasure, Autogenic-Feedback Training Exercise (AFTE) designed to prevent and/or correct adverse effects, i.e., facilitate adaptation to space and re-adaptation to Earth. AFTE is a six-hour physiological training program that has proven to be a highly efficient and effective method for enabling people to monitor and voluntarily control a range of their own physiological responses, thereby minimizing adverse reactions to environmental stress. However, because of limited opportunities to test this technology with space flight crews, it is essential to find operational or 'real world' environments in which to validate the efficacy of this approach.

Cowings, Patricia S.↗

NASA NTRS2000

NASA SMART Probe: Breast Cancer Application

There is evidence in breast cancer and other malignancies that the physiologic environment within a tumor correlates with clinical outcome. We are developing a unique percutaneous Smart Probe to be used at the time of needle biopsy of the breast. The Smart Probe will simultaneously measure multiple physiologic parameters within a breast tumor. Direct and indirect measurements of tissue oxygen levels, blood flow, pH, and tissue fluid pressure will be analyzed in real-time. These parameters will be interpreted individually and collectively by innovative neural network techniques using advanced intelligent software. The goals are 1) develop a pecutaneous Smart Probe with multiple sensor modalities and applying advanced Information Technologies to provide real time diagnostic information of the tissue at tip of the probe, 2) test the percutaneous Smart Probe in women with benign and malignant breast masses who will be undergoing surgical biopsy, 3) correlate probe sensor data with benign and malignant status of breast masses, 4) determine whether the probe can detect physiologic differences within a breast tumor, and its margins, and in adjacent normal breast tissue, 5) correlate probe sensor data with known prognostic factors for breast caner, including tumor size, tumor grade, axillary lymph node metastases, estrogen receptor and progesterone receptor status.

Mah, Robert W.↗

NASA NTRS1994

Assessment of Psychophysiological Responses During Motion Sickness Testing

The purpose of this investigation is to evaluate a methodology designed to accurately trace the temporal progression of motion sickness and space motion sickness symptoms. With this method, subjects continuously monitor their own motion sickness symptoms during exposure to a provocative stimulus as symptoms occur, in contrast to previous methods during which subjects report symptoms verbally at discrete time intervals. This method not only is comparable to previous methods in the type of symptoms that subjects report, but subjects report symptoms more frequently. Frequent reporting of motion sickness symptoms allows researchers to detail the waxing and waning of motion sickness symptoms for each individual. Previous research has shown that physiological responses to motion sickness stimuli are characterized by unique individual differences in response patterns. By improving our assessment of motion sickness symptoms with continuous monitoring of symptoms, the relationship between specific physiological responses and sickness levels can be more accurately determined for each individual. Results from this study show significant positive relationships between skin conductance levels and symptom levels for ten individuals; a significant positive relationship between temperature and symptom levels for 5 of 10 individuals; and both positive and negative relationships between respiration, heart rate, blood volume pulse and symptom levels. Continuous monitoring of motion sickness symptoms can be used to more accurately assess motion sickness to aid in the evaluation of countermeasures. In addition, recognition of the onset of symptoms that are strongly related to specific physiological responses could be used as cues to initiate procedures (e.g., Autogenic Feedback Training) to prevent the development of severe motion sickness symptoms.

Stoud, Cynthia S.↗

NASA NTRS2001

Organization of P, S, and Fe Inclusions in a Freshwater Magnetococcus

Magnetotactic bacteria are a heterogeneous group of motile, mainly aquatic procaryotes that align and swim along geomagnetic field lines. They are of interest to astrobiologists because of the magnetite crystals found in the Mars meteorite ALH84001 which share many characteristics with the magnetite produced intracellularly by magnetotactic bacteria. These bacteria are diverse morphologically, physiologically and phylogenetically, sharing a few key characteristics: 1) the presence of intracellular membrane-bound magnetic crystals (magnetosomes), usually but not always arranged in chains; 2) motility by means of flagella; and 3) microaerophillic or anaerobic physiology. The bilophotrichous (having two flagella bundles) magnetotactic cocci (MC) are ubiquitous in aquatic habitats but have proven extremely difficult to cultivate. Because only several marine strains have been isolated and grown in axenic culture, little is known about the physiology and the biogeochemical roles of the MC. We studied the composition and distribution of intracellular structures in an uncultured MC, designated ARB-1. To do this, a combination of light microscopy, environmental scanning electron microscopy (ESEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were used. Cells of ARB-1 were separated from sediments collected from Baldwin Lake (Los Angeles Arboretum, Arcadia, CA). They are large spherical to oblate spheroidal Gram-negative cells, ranging from 1 to 4 micrometers along the maximum dimension, which is perpendicular to the direction of swimming. Cells have two large phosphorus-containing inclusions that comprise a large percentage of the cell volume. Many smaller sulfur inclusions are located at the convex end of the cell. Most of the cellular Fe is present in the magnetosomes. These may be arranged as a clump at the concave end of the cell, near the two flagella bundles, or as chains, or as both a clump and chains. The magnetosomes were identified as magnetite (Fe3O4) by selected area electron diffraction (SAED) and high resolution TEM. We saw a trend between cell size and organization of the magnetosomes. Smaller, more spherical cells were more likely to have chains than were larger, more oblate cells. This may indicate different populations of cells, or it may be attributed to variations in cell growth cycle. The size distribution (length) of magnetosomes in chains was similar to that of magnetosomes in clusters, except that there was a larger size range for clustered magnetosomes. Magnetosomes from ARB-1 cells average 82 nm in length. If plotted on a graph of length as a function of aspect ratio, they fall within the single domain region of the plot. If compared with the size distributions of magnetite from ALH84001 and magnetosomes from the cultured magnetotactic vibrio MV-1, the magnetites produced by ARB-1 cells are, on average, larger and have a wider range of aspect ratio. ARB-1 cells have a specific organization of the P, S, and Fe inclusions. The P inclusions always occupy the majority of the cell volume and separate the S inclusions from the disorganized clumps of magnetosomes and the flagella bundles. The P inclusions may contain polyphosphate, which could play several roles in motility, adaptation to stress, growth and division, buoyancy, and energy. The S inclusions might be a way to store S, a potential energy source, when the cells move from sulfide to oxygen zones. The consistency of P, S, and Fe organization in ARB-1 cells suggests that these inclusions have some specific and interactive functions.

Cox, Lea↗