Analysis of Growth Characteristics and Differentially Expressed Homologous Genes in Rhodobacter sphaeroides under Normal and Simulated Microgravity Conditions

The term “microgravity” is used to describe the “weightlessness” or “zero-g” circumstances that can only be found in space beyond earth’s atmosphere. Rhodobacter sphaeroides is a gram-negative purple phototroph, used as a model organism for this study due to its genomic complexity and metabolic versatility. Its genome has been completely sequenced, and profiles of the differential gene expression under aerobic, semi-aerobic, and photosynthetic conditions were examined. In this study, we hypothesized that R. sphaeroides will show altered growth characteristics, morphological properties, and gene expression patterns when grown under simulated microgravity. To test that, we measured the optical density and colony-forming units of cell cultures grown under both microgravity and normal gravity conditions. Differences in the cell morphology were observed using scanning electron microscopy (SEM) images by measuring the length and the surface area of the cells under both conditions. Furthermore, we also identified homologous genes of R. spheroides using the differential gene expression study of Acidovorax under microgravity in our laboratory. Growth kinetics results showed that R. sphaeroides cells grown under microgravity experience a shorter log phase and early stationary phase compared to the cells growing under normal gravity conditions. The length and surface area of the cells under microgravity were significantly higher confirming that bacterial cells experience altered morphological features when grown under microgravity conditions. Differentially expressed homologous gene analysis indicated that genes coding for several COG and GO functions, such as metabolism, signal-transduction, transcription, translation, chemotaxis, and cell motility are differentially expressed to adapt and survive microgravity.

Recent Progress of Microgravity Science Research in China

Microgravity science is an important branch of space science.Its major objective is to study the laws of materials movement in microgravity,as well as to reveal the influence of gravity on the movement of materials in different gravity environments.Application researches relevant to these basic studies are also important contents of microgravity science.The advanced subjects,to some extent,reflect the ability of human beings to understand nature and the R&D level in this field in various countries.In this paper,the recent progress and the latest achievements of microgravity science and application researches in China aboard space platforms such as the Core Capsule Tianhe of the China Space Station(CSS)and satellites,as well as utilizing ground-based short-term microgravity facilities such as the Drop Tower Beijing and TUFF,are summarized,which cover the following sub-disciplines:microgravity fluid physics,microgravity combustion science,space materials science,space fundamental physics,space bio-technology,and relevant space technology applications.

SJ-10 Recoverable Satellite for Space Microgravity Experiments

SJ-10 is a recoverable scientific experiment satellite specially for the space experiments of microgravity physics science and space life science.This mission was officially started on 31 December 2012,and the satellite was launched on 6 April 2016.This paper introduces briefly the SJ-10 mission,the progress of SJ-10 engineering and the project constitution of sciences experiments onboard SJ-10.The purpose of this mission is to discover the law of matter movement and the rule of life activity that cannot be discovered on the ground due to the existence of gravity,and to know the acting mechanism on organisms by the complex radiation of space that cannot be simulated on the ground.

Simulated Microgravity Conditions and Carbon Ion Irradiation Induce Spermatogenic Cell Apoptosis and Sperm DNA Damage

Objective To investigate the effect of simulated microgravity and carbon ion irradiation （CIR） on spermatogenic cell apoptosis and sperm DNA damage to the testis of male Swiss Webster mice, and assess the risk associated with space environment. Methods Sperm DNA damage indicated by DNA fragmentation index （DFI） and high DNA stainability （HDS） was measured by sperm chromatin structure assay （SCSA）. Apoptosis of spermatogenic cells was detected by annexin V-propidium iodide assay. Bax （the expression levels of p53） and proliferating cell nuclear antigen （PCNAI were measured by immunoblotting; p53 and PCNA were located by immunohistology. Results HDS, DFI, apoptosis index, and the expression levels of p53 and Bax were detected to be significantly higher in the experimental groups （P〈0.05） compared with those in the control group, however, the PCNA expression varied to a certain degree, p53- and PCNA- positive expression were detected in each group, mainly in relation to the spermatogonic cells and spermatocytes. Conclusion The findings of the present study demonstrated that simulated microgravity and CIR can induce spermatogenic cell apoptosis and sperm DNA damage. Sperm DNA damage may be one of the underlying mechanisms behind male fertility decline under space environment. These findings may provide a scientific basis for protectint~ astronauts and space traveler＇s health and safety.

Effects of spaceflight and simulated microgravity on microbial growth and secondary metabolism

Spaceflight and ground-based microgravity analog experiments have suggested that microgravity can affect microbial growth and metabolism. Although the effects of microgravity and its analogs on microorganisms have been studied for more than 50 years, plausible conflicting and diverse results have frequently been reported in different experiments, especially regarding microbial growth and secondary metabolism. Until now, only the responses of a few typical microbes to microgravity have been investigated; systematic studies of the genetic and phenotypic responses of these microorganisms to microgravity in space are still insufficient due to technological and logistical hurdles. The use of different test strains and secondary metabolites in these studies appears to have caused diverse and conflicting results. Moreover, subtle changes in the extracellular microenvironments around microbial cells play a key role in the diverse responses of microbial growth and secondary metabolisms. Therefore, "indirect" effects represent a reasonable pathway to explain the occurrence of these phenomena in microorganisms. This review summarizes current knowledge on the changes in microbial growth and secondary metabolism in response to spaceflight and its analogs and discusses the diverse and conflicting results. In addition, recommendations are given for future studies on the effects of microgravity in space on microbial growth and secondary metabolism.

Differentiation of Mesenchymal Stem Cells towards a Nucleus Pulposus-like Phenotype Utilizing Simulated Microgravity In Vitro

Mesenchymal stem cells （MSCs） were induced into a nucleus pulposus-like phenotype utilizing simulated microgravity in vitro in order to establish a new cell-based tissue engineering treatment for intervertebral disc degeneration. For induction of a nucleus pulposus-like phenotype, MSCs were cultured in simulated microgravity in a chemically defined medium supplemented with 0 （experimental group） and 10 ng/mL （positive control group） of transforming growth factor β1 （TGF-β1）. MSCs cultured under conventional condition without TGF-β1 served as blank control group. On the day 3 of culture, cellular proliferation was determined by WST-8 assay. Differentiation markers were evaluated by histology and reverse transcriptase-polymerase chain reaction （RT-PCR）. TGF-β1 slightly promoted the proliferation of MSCs. The collagen and proteoglycans were detected in both groups after culture for 7 days. The accumulation of proteoglycans was markedly increased. The RT-PCR revealed that the gene expression of Sox-9, aggrecan and type Ⅱ collagen, which were chondrocyte specific, was increased in MSCs cultured under simulated microgravity for 3 days. The ratio of proteoglycans/collagen in blank control group was 3.4-fold higher than positive control group, which denoted a nucleus pulposus-like phenotype differentiation. Independent, spontaneous differentiation of MSCs towards a nucleus pulposus-like phenotype in simulated microgravity occurred without addition of any external bioactive stimulators, namely factors from TGF-β family, which were previously considered necessary.

Effect of Simulated Microgravity and its Associated Mechanism on Pulmonary Circulation in Rats

Objective To study the effect of Simulated Microgravity and its Associated Mechanism on Pulmonary Circulation in Rats. Methods Rat tail-suspension model was used to simulate the physiological effects of microgravity and changes in pulmonary blood vessel morphology, pulmonary arterial and venous blood pressure, pulmonary vascular resistance, pulmonary vasomotoricity, as well as the regulation of pulmonary circulation by cytokines produced and released by the lung of rats were measured. Results The walls of pulmonary blood vessels of rats were thickened, and the pulmonary artery was reconstructed with increased pulmonary vascular resistance. The pulmonary blood vessels of rats became more prone to dilation as contractions increased. Rat epithelial Adrenomedulin gene transcription and protein expression were upregulated. The level of basic fibroblast growth Factor of rat was also elevated. Conclusion Findings from the present study on rats revealed that the microgravity can affect pulmonary blood vessel structure, pulmonary arterial pressure, and pulmonary blood vessel self-regulation and cytokine production.

Progress on Microgravity Sciences in China

The main progress of the research activities on microgravity fluid physics, combustion, biotechnology research and fundamental Physics in China are briefly summarized in the present paper. The major space missions and experimental results obtained on board the Chinese recoverable/nonrecoverable satellites and the Chinese manned spaceship named "Shen Zhou" are presented summarily. The recent main activities of the ground-based studies in China are introduced in brief.

The Impacts of Simulated Microgravity on Rat Brain Depended on Durations and Regions

Objective To explore the dynamic impacts of simulated microgravity(SM) on different vital brain regions of rats. Methods Microgravity was simulated for 7 and 21 days, respectively, using the tail-suspension rat model. Histomorphology, oxidative stress, inflammatory cytokines and the expression of some key proteins were determined in hippocampus, cerebral cortex and striatum. Results 21-day SM decreased brain derived neurotrophic factor and induced neuron atrophy in the cerebral cortex. Strong oxidative stress was triggered at day 7 and the oxidative status returned to physiological level at day 21. Inflammatory cytokines were gradually suppressed and in striatum, the suppression was regulated partially through c-Jun/c-Fos. Conclusion The results revealed that the significant impacts of SM on rat brain tissue depended on durations and regions, which might help to understand the health risk and to prevent brain damage for astronauts in space travel.

Mitochondrial Oxidative Stress Enhances Vasoconstriction by Altering Calcium Homeostasis in Cerebrovascular Smooth Muscle Cells under Simulated Microgravity

Objective Exposure to microgravity results in postflight cardiovascular deconditioning in astronauts.Vascular oxidative stress injury and mitochondrial dysfunction have been reported during this process.To elucidate the mechanism for this condition,we investigated whether mitochondrial oxidative stress regulates calcium homeostasis and vasoconstriction in hindlimb unweighted(HU)rat cerebral arteries.Methods Three-week HU was used to simulate microgravity in rats.The contractile responses to vasoconstrictors,mitochondrial fission/fusion,Ca^(2+) distribution,inositol 1,4,5-trisphosphate receptor(IP3 R)abundance,and the activities of voltage-gated K+channels(KV)and Ca^(2+)-activated K+channels(BKCa)were examined in rat cerebral vascular smooth muscle cells(VSMCs).Results An increase of cytoplasmic Ca^(2+) and a decrease of mitochondrial/sarcoplasmic reticulum(SR)Ca^(2+) were observed in HU rat cerebral VSMCs.The abundance of fusion proteins(mitofusin 1/2[MFN1/2])and fission proteins(dynamin-related protein 1[DRP1]and fission-mitochondrial 1[FIS1])was significantly downregulated and upregulated,respectively in HU rat cerebral VSMCs.The cerebrovascular contractile responses to vasoconstrictors were enhanced in HU rats compared to control rats,and IP3 R protein/mRNA levels were significantly upregulated.The current densities and open probabilities of KV and BKCa decreased and increased,respectively.Treatment with the mitochondrial-targeted antioxidant mitoTEMPO attenuated mitochondrial fission by upregulating MFN1/2 and downregulating DRP1/FIS1.It also decreased IP3 R expression levels and restored the activities of the KV and BKCa channels.MitoTEMPO restored the Ca^(2+) distribution in VSMCs and attenuated the enhanced vasoconstriction in HU rat cerebral arteries.Conclusion The present results suggest that mitochondrial oxidative stress enhances cerebral vasoconstriction by regulating calcium homeostasis during simulated microgravity.

MICROGRAVITY EXPERIMENTS OF TWO-PHASE FLOW PATTERNS ABOARD MIR SPACE STATION

A first experimental study on two-phase how patterns at a long-term, steady microgravity condition was conducted on board the Russian Space Station 'MIR' in August 1999. Carbogal and air are used as the liquid and the gas phase, respectively. Bubble, slug, slug-annular transitional, and annular hows are observed. A new region of annular how with lower liquid superficial velocity is discovered, and the region of the slug-annular transitional flow is wider than that observed by experiments on board the parabolic aircraft. The main patterns are bubble, slug-annular transitional and annular flows based on the experiments on board MIR space station. Some influences on the two-phase how patterns in the present experiments are discussed.

Bone Loss Induced by Simulated Microgravity,Ionizing Radiation and/or Ultradian Rhythms in the Hindlimbs of Rats

Objective To better understand the pathological causes of bone loss in a space environment, including microgravity, ionizing radiation, and ultradian rhythms.Methods Sprague Dawley （SD） rats were randomly divided into a baseline group, a control group, a hindlimb suspension group, a radiation group, a ultradian rhythms group and a combined-three-factor group. After four weeks of hindlimb suspension followed by X-ray exposure and/or ultradian rhythms, biomechanical properties, bone mineral density, histological analysis, microstructure parameters, and bone turnover markers were detected to evaluate bone loss in hindlimbs of rats.Results Simulated microgravity or combined-three factors treatment led to a significant decrease in the biomechanical properties of bones, reduction in bone mineral density, and deterioration of trabecular parameters. Ionizing radiation exposure also showed adverse impact while ultradian rhythms had no significant effect on these outcomes. Decrease in the concentration of the turnover markers bone alkaline phosphatase （bALP）, osteocalcin （OCN）, and tartrate-resistant acid phosphatase-5b （TRAP-Sb） in serum was in line with the changes in trabecular parameters.Conclusion Simulated microgravity is the main contributor of bone loss. Radiation also results in deleterious effects but ultradian rhythms has no significant effect. Combined-three factors treatment do not exacerbate bone loss when compared to simulated microgravity treatment alone.

The study on the mechanical characteristics of articular cartilage in simulated microgravity

The microgravity environment of a long-term space flight may induce acute changes in an astronaut＇s musculo-skeletal systems. This study explores the effects of simulated microgravity on the mechanical characteristics of articular cartilage. Six rats underwent tail suspension for 14 days and six additional rats were kept under normal earth gravity as controls. Swelling strains were measured using high-frequency ultrasound in all cartilage samples subject to osmotic loading. Site-specific swelling strain data were used in a triphasic theoretical model of cartilage swelling to determine the uniaxial modulus of the cartilage solid matrix. No severe surface irregularities were found in the cartilage samples obtained from the control or tail-suspended groups. For the tail-suspended group, the thickness of the cartilage at a specified site, as determined by ultrasound echo, showed a minor decrease. The uniaxial modulus of articular cartilage at the specified site decreased significantly, from （6.31 ± 3.37） MPa to （5.05 ± 2.98）MPa （p 〈 0.05）. The histology- stained image of a cartilage sample also showed a reduced number of chondrocytes and decreased degree of matrix staining. These results demonstrated that the 14 d simulated microgravity induced significant effects on the mechanical characteristics of articular cartilage. This study is the first attempt to explore the effects of simulated microgravity on the mechanical characteristics of articular cartilage using an osmotic loading method and a triphasic model. The conclusions may provide reference information for manned space flights and a better understanding of the effects of microgravity on the skeletal system.

TWO-PHASE FLOW PATTERNS IN A 90° BEND AT MICROGRAVITY

Bends are widely used in pipelines carrying single-and two-phase fluids in both ground and space applications.In particular,they play more important role in space applications due to the extreme spatial constraints.In the present study,a set of experimental data of two-phase flow patterns and their transitions in a 90°bend with inner diameter of 12.7 mm and curvature radius of 76.5 mm at microgravity conditions are reported.Gas and liquid superficial velocities are found to range from (1.0～23.6)m/s for gas and(0.09～0.5)m/s for liquid,respectively.Three major flow patterns, namely slug,slug-annular transitional,and annular flows,are observed in this study.Focusing on the differences between flow patterns in bends and their counterparts in straight pipes,detailed analyses of their characteristics are made.The transitions between adjoining flow patterns are found to be more or less the same as those in straight pipes,and can be predicted using Weber number models satisfactorily. The reasons for such agreement are carefully examined.

Experimental and numerical study on energy dissipation in freely cooling granular gases under microgravity

Energy dissipation is one of the most important properties of granular gas, which makes Its behavior dltterent trom that of molecular gas. In this work we report our investigations on the freely-cooling evolution of granular gas under microgravity in a drop tower experiment, and also conduct the molecular dynamics （MD） simulation for comparison. While our experimental and simulation results support Haff＇s law that the kinetic energy dissipates with time t as E（t） （1 ＋ t/v） 2, we modify ~＂ by taking into account the friction dissipation during collisions, and study the effects of number density and particle size on the collision frequency. From the standard deviation of the measured velocity distributions we also verify the energy dissipation law, which is in agreement with Haff＇s kinetic energy dissipation.

Nonlinear coupled dynamics of liquid-filled spherical container in microgravity

Nonlinear coupled dynamics of a liquid-filled spherical container in microgravity are investigated. The governing equations of the low-gravity liquid sloshing in a convex axisymmetrical container subjected to lateral excitation is obtained by the variational principle and solved with a modal analysis method. The variational formulas are transformed into a frequency equation in the form of a standard eigenvalue problem by the Galerkin method, in which admissible functions for the velocity potential and the liquid flee surface displacement are determined analytically in terms of the Gaussian hypergeometric series. The coupled dynamic equations of the liquid-filled container are derived using the Lagrange＇s method and are numerically solved. The time histories of the modal solutions are obtained in numerical simulations.

MICROSTRUCTURAL FEATURE OF Al-In MONOTECTIC ALLOY PROCESSED UNDER MICROGRAVITY

The microstructural feature of Al-In monotectic alloy processed under microgravity has been investigated It was found that in the sample cooled in space,there are a lot of In particles in A! dendrite,but no particle has been observed in the sample cooled on the ground.Moreover, the In particles distribute with regularity and the A1 dendrite has an obvious boundary layer marked by a string of particles.Thus,the distinction between them may reflect the character- istics of the solid/liquid interface during solidification under different gravity conditions.

Effects of simulated microgravity on antioxidant system in testis of adult rats

Objective： To study the effects of simulated microgravity induced by tail-suspension on histological structures and antioxidant system in testis of adult rats. Methods： Forty Spraque-Dawley adult male rats were randomly divided into four groups, two experimental groups and two synchronic control groups. Rats in the two experimental groups were tail-suspended for 14 d and 28 d respectively, then serum hormone, testicular morphology and biochemical changes were evaluated. Results： Compared with the synchronic controls, serum testosterone （T） levels and testicular superoxide dismutase （SOD） significantly decreased（P 〈 0.05）, while testicular malondialdehyde（MDA） significantly increased （P 〈 0.05） in tail-suspended rats. The changes were more prominent in the 28 d tail-suspended rats. In addition, hematoxylin and eosin （HE） staining showed that seminiferous tubules atrophied, spermatogenic cells decreased, and seminiferous epithelial cells disintegrated and shed, abnormal multinucleated giant cells appeared and the lumina were azoospermic in tail-suspended rats. ConcIusion： Simulated microgravity induced by tailsuspension has a harmful effect on male reproduction of adult rats by decreasing the ability of testicular antioxidant defense.

Protective effects of Dragon's Blood on blood coagulation and NO/iNOS level in myocardium and serum of rats in simulated microgravity

To investigate effects of Dragon＇s Blood（DB）,a traditional Chinese medicine,on blood coagulation and NO/iNOS level in myocardium and serum of rats in simulated microgravity for the first time,Sprague Dawley（SD）rats were randomly divided into six groups：（a）5-day control group,（b）5-day model group,（c）5-day drug group,（d）21-day control group,（e）21-day model group,and（f）21-day drug group.Blood coagulation and NO/iNOS level in myocardium and serum were examined after 5 and 21 days of simulated microgravity respectively.The results showed that blood of tail-suspended rats was in a hypercoagulable state that could not be converted with time extending.Conversely,DB changed these parameters towards normal level and the curative effects became better when tail-suspension lasted till the 21 st day.NO concentration of both myocardium and serum for two periods all increased markedly and DB could effectively reduce these increases except that of 21-day myocardium NO.Activity of iNOS increased markedly as early as 5 days and became more serious on the 21 st day,while DB showed preventive effect on the 21 st day.Western Blot analysis illustrated that the expression of iNOS in the 5-day model group increased significantly over the 5-day control group and the expression in the 5-day drug group dramatically returned to the normal level.The similar trend was observed on the 21-day groups without notable variances.The findings of this study can serve for the further use of Dragon＇s Blood in space diseases.

Capillary Rise between Parallel Perforated Plates in Microgravity

This paper presents the setup and performance of a drop tower experiment which investigates the behavior of liquid during self-driven capillary transport between two parallel perforated plates under microgravity. With the onset ofmicrogravity the liquid rises between the two parallel plates as a result of capillary pressure. Eight different sets of plates are tested in this study and the free surface height and the volume of transported liquid is subsequently analyzed. The plate sets differ in geometric properties of their perforations, distance, and width. In each set the perforations of both plates are identical and have a diameter of a few millimeters. The capillary rise velocity is influenced by the perforation diameter and the area porosity of the plates. As could be expected, the capillary transport capability increases with decreasing plate porosity.