Space microbiology

The Impacts of Microgravity on Bacterial Metabolism

The inside of a space-faring vehicle provides a set of conditions unlike anything experienced by bacteria on Earth. The low-shear, diffusion-limited microenvironment with accompanying high levels of ionizing radiation create high stress in bacterial cells, and results in many physiological adaptations. This review gives an overview of the effect spaceflight in general, and real or simulated microgravity in particular, has on primary and secondary metabolism. Some broad trends in primary metabolic responses can be identified. These include increases in carbohydrate metabolism, changes in carbon substrate utilization range, and changes in amino acid metabolism that reflect increased oxidative stress. However, another important trend is that there is no universal bacterial response to microgravity, as different bacteria often have contradictory responses to the same stress. This is exemplified in many of the observed secondary metabolite responses where secondary metabolites may have increased, decreased, or unchanged production in microgravity. Different secondary metabolites in the same organism can even show drastically different production responses. Microgravity can also impact the production profile and localization of secondary metabolites. The inconsistency of bacterial responses to real or simulated microgravity underscores the importance of further research in this area to better understand how microbes can impact the people and systems aboard spacecraft.

Absence of increased genomic variants in the cyanobacterium Chroococcidiopsis exposed to Mars-like conditions outside the space station

Despite the increasing interest in using microbial-based technologies to support human space exploration, many unknowns remain not only on bioprocesses but also on microbial survivability and genetic stability under non-Earth conditions. Here the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 was investigated for robustness of the repair capability of DNA lesions accumulated under Mars-like conditions (UV radiation and atmosphere) simulated in low Earth orbit using the EXPOSE-R2 facility installed outside the International Space Station. Genomic alterations were determined in a space-derivate of Chroococcidiopsis sp. CCMEE 029 obtained upon reactivation on Earth of the space-exposed cells. Comparative analysis of whole-genome sequences showed no increased variant numbers in the space-derivate compared to triplicates of the reference strain maintained on the ground. This result advanced cyanobacteria-based technologies to support human space exploration.

CAMDLES: CFD-DEM Simulation of Microbial Communities in Spaceflight and Artificial Microgravity

We present CAMDLES (CFD-DEM Artificial Microgravity Developments for Living Ecosystem Simulation), an extension of CFDEM^®Coupling to model biological flows, growth, and mass transfer in artificial microgravity devices. For microbes that accompany humans into space, microgravity-induced alterations in the fluid environment are likely to be a major factor in the microbial experience of spaceflight. Computational modeling is needed to investigate how well ground-based microgravity simulation methods replicate that experience. CAMDLES incorporates agent-based modeling to study inter-species metabolite transport within microbial communities in rotating wall vessel bioreactors (RWVs). Preexisting CFD modeling of RWVs has not yet incorporated growth; CAMDLES employs the simultaneous modeling of biological, chemical, and mechanical processes in a micro-scale rotating reference frame environment. Simulation mass transfer calculations were correlated with Monod dynamic parameters to predict relative growth rates between artificial microgravity, spaceflight microgravity, and 1 g conditions. By simulating a microbial model community of metabolically cooperative strains of Escherichia coli and Salmonella enterica, we found that the greatest difference between microgravity and an RWV or 1 g gravity was when species colocalized in dense aggregates. We also investigated the influence of other features of the system on growth, such as spatial distribution, product yields, and diffusivity. Our simulation provides a basis for future laboratory experiments using this community for investigation in artificial microgravity and spaceflight microgravity. More broadly, our development of these models creates a framework for novel hypothesis generation and design of biological experiments with RWVs, coupling the effects of RWV size, rotation rate, and mass transport directly to bacterial growth in microbial communities.

A Current Overview of the Biological Effects of Combined Space Environmental Factors in Mammals

Distinct from Earth’s environment, space environmental factors mainly include space radiation, microgravity, hypomagnetic field, and disrupted light/dark cycles that cause physiological changes in astronauts. Numerous studies have demonstrated that space environmental factors can lead to muscle atrophy, bone loss, carcinogenesis, immune disorders, vascular function and cognitive impairment. Most current ground-based studies focused on single environmental factor biological effects. To promote manned space exploration, a better understanding of the biological effects of the spaceflight environment is necessary. This paper summarizes the latest research progress of the combined biological effects of double or multiple space environmental factors on mammalian cells, and discusses their possible molecular mechanisms, with the hope of providing a scientific theoretical basis to develop appropriate countermeasures for astronauts.

Dermatitis during Spaceflight Associated with HSV-1 Reactivation

Human alpha herpesviruses herpes simplex virus (HSV-1) and varicella zoster virus (VZV) establish latency in various cranial nerve ganglia and often reactivate in response to stress-associated immune system dysregulation. Reactivation of Epstein Barr virus (EBV), VZV, HSV-1, and cytomegalovirus (CMV) is typically asymptomatic during spaceflight, though live/infectious virus has been recovered and the shedding rate increases with mission duration. The risk of clinical disease, therefore, may increase for astronauts assigned to extended missions (>180 days). Here, we report, for the first time, a case of HSV-1 skin rash (dermatitis) occurring during long-duration spaceflight. The astronaut reported persistent dermatitis during flight, which was treated onboard with oral antihistamines and topical/oral steroids. No HSV-1 DNA was detected in 6-month pre-mission saliva samples, but on flight day 82, a saliva and rash swab both yielded 4.8 copies/ng DNA and 5.3 × 104 copies/ng DNA, respectively. Post-mission saliva samples continued to have a high infectious HSV-1 load (1.67 × 107 copies/ng DNA). HSV-1 from both rash and saliva samples had 99.9% genotype homology. Additional physiological monitoring, including stress biomarkers (cortisol, dehydroepiandrosterone (DHEA), and salivary amylase), immune markers (adaptive regulatory and inflammatory plasma cytokines), and biochemical profile markers, including vitamin/mineral status and bone metabolism, are also presented for this case. These data highlight an atypical presentation of HSV-1 during spaceflight and underscore the importance of viral screening during clinical evaluations of in-flight dermatitis to determine viral etiology and guide treatment.

The effects of microgravity on bone structure and function

Humans are spending an increasing amount of time in space, where exposure to conditions of microgravity causes 1-2% bone loss per month in astronauts. Through data collected from astronauts, as well as animal and cellular experiments conducted in space, it is evident that microgravity induces skeletal deconditioning in weight-bearing bones. This review identifies contentions in current literature describing the effect of microgravity on non-weight-bearing bones, different bone compartments, as well as the skeletal recovery process in human and animal spaceflight data. Experiments in space are not readily available, and experimental designs are often limited due to logistical and technical reasons. This review introduces a plethora of on-ground research that elucidate the intricate process of bone loss, utilising technology that simulates microgravity. Observations from these studies are largely congruent to data obtained from spaceflight experiments, while offering more insights behind the molecular mechanisms leading to microgravity-induced bone loss. These insights are discussed herein, as well as how that knowledge has contributed to studies of current therapeutic agents. This review also points out discrepancies in existing data, highlighting knowledge gaps in our current understanding. Further dissection of the exact mechanisms of microgravity-induced bone loss will enable the development of more effective preventative and therapeutic measures to protect against bone loss, both in space and possibly on ground.

The Space-Exposed Kombucha Microbial Community Member Komagataeibacter oboediens Showed Only Minor Changes in Its Genome After Reactivation on Earth

Komagataeibacter is the dominant taxon and cellulose-producing bacteria in the Kombucha Microbial Community (KMC). This is the first study to isolate the K. oboediens genome from a reactivated space-exposed KMC sample and comprehensively characterize it. The space-exposed genome was compared with the Earth-based reference genome to understand the genome stability of K. oboediens under extraterrestrial conditions during a long time. Our results suggest that the genomes of K. oboediens IMBG180 (ground sample) and K. oboediens IMBG185 (space-exposed) are remarkably similar in topology, genomic islands, transposases, prion-like proteins, and number of plasmids and CRISPR-Cas cassettes. Nonetheless, there was a difference in the length of plasmids and the location of cas genes. A small difference was observed in the number of protein coding genes. Despite these differences, they do not affect any genetic metabolic profile of the cellulose synthesis, nitrogen-fixation, hopanoid lipids biosynthesis, and stress-related pathways. Minor changes are only observed in central carbohydrate and energy metabolism pathways gene numbers or sequence completeness. Altogether, these findings suggest that K. oboediens maintains its genome stability and functionality in KMC exposed to the space environment most probably due to the protective role of the KMC biofilm. Furthermore, due to its unaffected metabolic pathways, this bacterial species may also retain some promising potential for space applications.

A material-based panspermia hypothesis: The potential of polymer gels and membraneless droplets

The Panspermia hypothesis posits that either life's building blocks (molecular Panspermia) or life itself (organism-based Panspermia) may have been interplanetarily transferred to facilitate the origins of life (OoL) on a given planet, complementing several current OoL frameworks. Although many spaceflight experiments were performed in the past to test for potential terrestrial organisms as Panspermia seeds, it is uncertain whether such organisms will likely "seed" a new planet even if they are able to survive spaceflight. Therefore, rather than using organisms, using abiotic chemicals as seeds has been proposed as part of the molecular Panspermia hypothesis. Here, as an extension of this hypothesis, we introduce and review the plausibility of a polymeric material-based Panspermia seed (M-BPS) as a theoretical concept, where the type of polymeric material that can function as a M-BPS must be able to: (1) survive spaceflight and (2) "function", i.e., contingently drive chemical evolution toward some form of abiogenesis once arriving on a foreign planet. We use polymeric gels as a model example of a potential M-BPS. Polymeric gels that can be prebiotically synthesized on one planet (such as polyester gels) could be transferred to another planet via meteoritic transfer, where upon landing on a liquid bearing planet, can assemble into structures containing cellular-like characteristics and functionalities. Such features presupposed that these gels can assemble into compartments through phase separation to accomplish relevant functions such as encapsulation of primitive metabolic, genetic and catalytic materials, exchange of these materials, motion, coalescence, and evolution. All of these functions can result in the gels' capability to alter local geochemical niches on other planets, thereby allowing chemical evolution to lead to OoL events.

Combined Impact of Magnetic Force and Spaceflight Conditions on Escherichia Coli Physiology

Changes in bacterial physiology caused by the combined action of the magnetic force and microgravity were studied in Escherichia coli grown using a specially developed device aboard the International Space Station. The morphology and metabolism of E. coli grown under spaceflight (SF) or combined spaceflight and magnetic force (SF + MF) conditions were compared with ground cultivated bacteria grown under standard (control) or magnetic force (MF) conditions. SF, SF + MF, and MF conditions provided the up-regulation of Ag43 auto-transporter and cell auto-aggregation. The magnetic force caused visible clustering of non-sedimenting bacteria that formed matrix-containing aggregates under SF + MF and MF conditions. Cell auto-aggregation was accompanied by up-regulation of glyoxylate shunt enzymes and Vitamin B12 transporter BtuB. Under SF and SF + MF but not MF conditions nutrition and oxygen limitations were manifested by the down-regulation of glycolysis and TCA enzymes and the up-regulation of methylglyoxal bypass. Bacteria grown under combined SF + MF conditions demonstrated superior up-regulation of enzymes of the methylglyoxal bypass and down-regulation of glycolysis and TCA enzymes compared to SF conditions, suggesting that the magnetic force strengthened the effects of microgravity on the bacterial metabolism. This strengthening appeared to be due to magnetic force-dependent bacterial clustering within a small volume that reinforced the effects of the microgravity-driven absence of convectional flows.

Spaceflight Virology: What Do We Know about Viral Threats in the Spaceflight Environment?

Viruses constitute a significant part of the human microbiome, so wherever humans go, viruses are brought with them, even on space missions. In this mini review, we focus on the International Space Station (ISS) as the only current human habitat in space that has a diverse range of viral genera that infect microorganisms from bacteria to eukaryotes. Thus, we have reviewed the literature on the physical conditions of space habitats that have an impact on both virus transmissibility and interaction with their host, which include UV radiation, ionizing radiation, humidity, and microgravity. Also, we briefly comment on the practices used on space missions that reduce virus spread, that is, use of antimicrobial surfaces, spacecraft sterilization practices, and air filtration. Finally, we turn our attention to the health threats that viruses pose to space travel. Overall, even though efforts are taken to ensure safe conditions during human space travel, for example, preflight quarantines of astronauts, we reflect on the potential risks humans might be exposed to and how those risks might be aggravated in extraterrestrial habitats.

Incidence of Phage Capsid Organization on the Resistance to High Energy Proton Beams

The helical geometry of virus capsid allows simple self-assembly of identical protein subunits with a low request of free energy and a similar spiral path to virus nucleic acid. Consequently, small variations in protein subunits can affect the stability of the entire phage particle. Previously, we observed that rearrangement in the capsid structure of M13 engineered phages affected the resistance to UV-C exposure, while that to H2O2 was mainly ascribable to the amino acids’ sequence of the foreign peptide. Based on these findings, in this work, the resistance to accelerated proton beam exposure (5.0 MeV energy) of the same phage clones was determined at different absorbed doses and dose rates. Then, the number of viral particles able to infect and replicate in the natural host, Escherichia coli F+, was evaluated. By comparing the results with the M13 wild-type vector (pC89), we observed that 12III1 phage clones, with the foreign peptide containing amino acids favorable to carbonylation, exhibited the highest reduction in phage titer associated with a radiation damage (RD) of 35 × 10−3/Gy at 50 dose Gy. On the other hand, P9b phage clones, containing amino acids unfavorable to carbonylation, showed the lowest reduction with an RD of 4.83 × 10−3/Gy at 500 dose Gy. These findings could improve the understanding of the molecular mechanisms underlying the radiation resistance of viruses

Effects of Ionizing Radiation and Long-Term Storage on Hydrated vs. Dried Cell Samples of Extremophilic Microorganisms

A main factor hampering life in space is represented by high atomic number nuclei and energy (HZE) ions that constitute about 1% of the galactic cosmic rays. In the frame of the "STARLIFE" project, we accessed the Heavy Ion Medical Accelerator (HIMAC) facility of the National Institute of Radiological Sciences (NIRS) in Chiba, Japan. By means of this facility, the extremophilic species Haloterrigena hispanica and Parageobacillus thermantarcticus were irradiated with high LET ions (i.e., Fe, Ar, and He ions) at doses corresponding to long permanence in the space environment. The survivability of HZE-treated cells depended upon either the storage time and the hydration state during irradiation; indeed, dry samples were shown to be more resistant than hydrated ones. With particular regard to spores of the species P. thermantarcticus, they were the most resistant to irradiation in a water medium: an analysis of the changes in their biochemical fingerprinting during irradiation showed that, below the survivability threshold, the spores undergo to a germination-like process, while for higher doses, inactivation takes place as a consequence of the concomitant release of the core's content and a loss of integrity of the main cellular components. Overall, the results reported here suggest that the selected extremophilic microorganisms could serve as biological model for space simulation and/or real space condition exposure, since they showed good resistance to ionizing radiation exposure and were able to resume cellular growth after long-term storage.

The smallest space miners: principles of space biomining

As we aim to expand human presence in space, we need to find viable approaches to achieve independence from terrestrial resources. Space biomining of the Moon, Mars and asteroids has been indicated as one of the promising approaches to achieve in-situ resource utilization by the main space agencies. Structural and expensive metals, essential mineral nutrients, water, oxygen and volatiles could be potentially extracted from extraterrestrial regolith and rocks using microbial-based biotechnologies. The use of bioleaching microorganisms could also be applied to space bioremediation, recycling of waste and to reinforce regenerative life support systems. However, the science around space biomining is still young. Relevant differences between terrestrial and extraterrestrial conditions exist, including the rock types and ores available for mining, and a direct application of established terrestrial biomining techniques may not be a possibility. It is, therefore, necessary to invest in terrestrial and space-based research of specific methods for space applications to learn the effects of space conditions on biomining and bioremediation, expand our knowledge on organotrophic and community-based bioleaching mechanisms, as well as on anaerobic biomining, and investigate the use of synthetic biology to overcome limitations posed by the space environments.

Interstellar space biology via Project Starlight

Our ability to explore the cosmos by direct contact has been limited to a small number of lunar and interplanetary missions. However, the NASA Starlight program points a path forward to send small, relativistic spacecraft far outside our solar system via standoff directed-energy propulsion. These miniaturized spacecraft are capable of robotic exploration but can also transport seeds and organisms, marking a profound change in our ability to both characterize and expand the reach of known life. Here we explore the biological and technological challenges of interstellar space biology, focusing on radiation-tolerant microorganisms capable of cryptobiosis. Additionally, we discuss planetary protection concerns and other ethical considerations of sending life to the stars.

Bridging the gap between microbial limits and extremes in space: space microbial biotechnology in the next 15 years

The establishment of a permanent human settlement in space is one of humanity's ambitions. To achieve this, microorganisms will be used to carry out many functions such as recycling, food and pharmaceutical production, mining and other processes. However, the physical and chemical extremes in all locations beyond Earth exceed known growth limits of microbial life. Making microbes more tolerant of a greater range of extraterrestrial extremes will not produce organisms that can grow in unmodified extraterrestrial environments since in many of them not even liquid water can exist. However, by narrowing the gap, the engineering demands on bioindustrial processes can be reduced and greater robustness can be incorporated into the biological component. I identify and describe these required microbial biotechnological modifications and speculate on long-term possibilities such as microbial biotechnology on Saturn's moon Titan to support a human presence in the outer Solar System and bioprocessing of asteroids. A challenge for space microbial biotechnology in the coming decades is to narrow the microbial gap by systemically identifying the genes required to do this and incorporating them into microbial systems that can be used to carry out bioindustrial processes of interest.

Long-Term Space Nutrition: A Scoping Review

This scoping review aimed to identify current evidence and gaps in the field of long-term space nutrition. Specifically, the review targeted critical nutritional needs during long-term manned missions in outer space in addition to the essential components of a sustainable space nutrition system for meeting these needs. The search phrase "space food and the survival of astronauts in long-term missions" was used to collect the initial 5432 articles from seven Chinese and seven English databases. From these articles, two independent reviewers screened titles and abstracts to identify 218 articles for full-text reviews based on three themes and 18 keyword combinations as eligibility criteria. The results suggest that it is possible to address short-term adverse environmental factors and nutritional deficiencies by adopting effective dietary measures, selecting the right types of foods and supplements, and engaging in specific sustainable food production and eating practices. However, to support self-sufficiency during long-term space exploration, the most optimal and sustainable space nutrition systems are likely to be supported primarily by fresh food production, natural unprocessed foods as diets, nutrient recycling of food scraps and cultivation systems, and the establishment of closed-loop biospheres or landscape-based space habitats as long-term life support systems.

Mechanobiological Implications of Cancer Progression in Space

The human body is normally adapted to maintain homeostasis in a terrestrial environment. The novel conditions of a space environment introduce challenges that changes the cellular response to its surroundings. Such an alteration causes physical changes in the extracellular microenvironment, inducing the secretion of cytokines such as interleukin-6 (IL-6) and tumor growth factor-β (TGF-β) from cancer cells to enhance cancer malignancy. Cancer is one of the most prominent cell types to be affected by mechanical cues via active interaction with the tumor microenvironment. However, the mechanism by which cancer cells mechanotransduce in the space environment, as well as the influence of this process on human health, have not been fully elucidated. Due to the growing interest in space biology, this article reviews cancer cell responses to the representative conditions altered in space: microgravity, decompression, and irradiation. Interestingly, cytokine and gene expression that assist in tumor survival, invasive phenotypic transformation, and cancer cell proliferation are upregulated when exposed to both simulated and actual space conditions. The necessity of further research on space mechanobiology such as simulating more complex in vivo experiments or finding other mechanical cues that may be encountered during spaceflight are emphasized.

Biotechnology under extreme conditions: Lichens after extreme UVB radiation and extreme temperatures produce large amounts of hydrogen

The present study demonstrates biotechnological applications of the lichen Pleurosticta acetabulum, specifically the production of large amounts of hydrogen even after the lichen exposure to extreme conditions such as a) extreme UVB radiation (1.7 mW/cm² = 1000 J m^-2 min^-1) over different time periods (4, 20 & 70 h) and b) combined exposure of the lichen to high intensity UVB radiation and extreme low (-196 °C) or extreme high temperatures (+70 °C). The results highlight that the extremophilic and polyextremophilic behavior of lichens both in dehydrated and in regenerated form, under extreme conditions not necessarily recorded on earth, is compatible with their biotechnological uses. The lichen viability was measured using fluorescence induction techniques (OJIP-test), which record changes in the molecular structure and function of the photosynthetic mechanism, while its ability to produce molecular hydrogen was measured through thermal conductivity gas chromatography (GC-TCD) analysis. Hydrogen is a promising fuel for the future. The exciting result of a lichen micro-ecosystem is its ability to expel its moisture and remain in an inactive state, protecting itself from extreme conditions and maintaining its ability to high yield hydrogen production in a closed system, with the sole addition of water and without the need for additional energy. Our results expand the potential use of lichens for future biotechnological applications in extreme Earth environments, but also in environments on other planets, such as Mars, thus paving the way for astrobiotechnological applications.

Identification of bacterial communities in extreme sites of Pakistan using high throughput barcoded amplicon sequencing

Microorganisms thrive nearly everywhere including extreme environments where few other forms of life can exist. Geochemistry of extreme sites plays a major role in shaping these microbial communities and microbes thriving in such harsh conditions are untapped sources of novel biomolecules. To understand the structure and composition of such microbial communities, culture-independent bacterial diversity was characterised for two extreme sites in Pakistan, Khewra salt range and Murtazaabad hot spring. Barcoded amplicon sequencing technique was used to study the microbial communities. Physicochemical analysis of these sites was also conducted to study the dynamics of microbial communities under stressed conditions. Metagenomic sequencing of salt range soil samples yielded of 40,433 16S rRNA sequences, while hot spring sediments produced 76,449 16S rRNA sequence reads. Proteobacteria were predominant in saline soil while Firmicutes were most abundant in hot spring sediment. The taxonomic analysis of saline samples revealed 914 operational taxonomic units (OTUs) while that of hot spring sequences were clustered into 726 distinct OTUs. OTUs from genus Alkalibacillus were most abundant in hot spring sediments, whereas Haloarcula were more prevalent in saline soil. Some unidentified sequences were also present at each taxonomic level. Multivariate analysis indicated that electrical conductivity and pH are the major environmental factors involved in modelling microbial communities. This study revealed a poly-extremophilic microbial community in the Murtazaabad hot spring and characterised the unexplored halophilic microbial diversity of saline soil of Pakistan.

Venus, an Astrobiology Target

We present a case for the exploration of Venus as an astrobiology target-(1) investigations focused on the likelihood that liquid water existed on the surface in the past, leading to the potential for the origin and evolution of life, (2) investigations into the potential for habitable zones within Venus' present-day clouds and Venus-like exo atmospheres, (3) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus' clouds and Venus-like atmospheres, and (4) application of these investigative approaches toward better understanding the atmospheric dynamics and habitability of exoplanets. The proximity of Venus to Earth, guidance for exoplanet habitability investigations, and access to the potential cloud habitable layer and surface for prolonged in situ extended measurements together make the planet a very attractive target for near term astrobiological exploration.

Exobiology of the Venusian Clouds: New Insights into Habitability through Terrestrial Models and Methods of Detection

The search for life beyond Earth has focused on Mars and the icy moons Europa and Enceladus, all of which are considered a safe haven for life due to evidence of current or past water. The surface of Venus, on the other hand, has extreme conditions that make it a nonhabitable environment to life as we know it. This is in contrast, however, to its cloud layer, which, while still an extreme environment, may prove to be a safe haven for some extreme forms of life similar to extremophiles on Earth. We consider the venusian clouds a habitable environment based on the presence of (1) a solvent for biochemical reactions, (2) appropriate physicochemical conditions, (3) available energy, and (4) biologically relevant elements. The diversity of extreme microbial ecosystems on Earth has allowed us to identify terrestrial chemolithoautotrophic microorganisms that may be analogs to putative venusian organisms. Here, we hypothesize and describe biological processes that may be performed by such organisms in the venusian clouds. To detect putative venusian organisms, we describe potential biosignature detection methods, which include metal-microbial interactions and optical methods. Finally, we describe currently available technology that can potentially be used for modeling and simulation experiments.

Effects of Simulated Microgravity on the Physiology of Stenotrophomonas maltophilia and Multiomic Analysis

Many studies have shown that the space environment plays a pivotal role in changing the characteristics of conditional pathogens, especially their pathogenicity and virulence. However, Stenotrophomonas maltophilia, a type of conditional pathogen that has shown to a gradual increase in clinical morbidity in recent years, has rarely been reported for its impact in space. In this study, S. maltophilia was exposed to a simulated microgravity (SMG) environment in high-aspect ratio rotating-wall vessel bioreactors for 14days, while the control group was exposed to the same bioreactors in a normal gravity (NG) environment. Then, combined phenotypic, genomic, transcriptomic, and proteomic analyses were conducted to compare the influence of the SMG and NG on S. maltophilia. The results showed that S. maltophilia in simulated microgravity displayed an increased growth rate, enhanced biofilm formation ability, increased swimming motility, and metabolic alterations compared with those of S. maltophilia in normal gravity and the original strain of S. maltophilia. Clusters of Orthologous Groups (COG) annotation analysis indicated that the increased growth rate might be related to the upregulation of differentially expressed genes (DEGs) involved in energy metabolism and conversion, secondary metabolite biosynthesis, transport and catabolism, intracellular trafficking, secretion, and vesicular transport. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the increased motility might be associated the upregulation of differentially expressed proteins (DEPs) involved in locomotion, localization, biological adhesion, and binding, in accordance with the upregulated DEGs in cell motility according to COG classification, including pilP, pilM, flgE, flgG, and ronN. Additionally, the increased biofilm formation ability might be associated with the upregulation of DEPs involved in biofilm formation, the bacterial secretion system, biological adhesion, and cell adhesion, which were shown to be regulated by the differentially expressed genes (chpB, chpC, rpoN, pilA, pilG, pilH, and pilJ) through the integration of transcriptomic and proteomic analyses. These results suggested that simulated microgravity might increase the level of corresponding functional proteins by upregulating related genes to alter physiological characteristics and modulate growth rate, motility, biofilm formation, and metabolism. In conclusion, this study is the first general analysis of the phenotypic, genomic, transcriptomic, and proteomic changes in S. maltophilia under simulated microgravity and provides some suggestions for future studies of space microbiology.

Longitudinal characterization of multispecies microbial populations recovered from spaceflight potable water

While sequencing technologies have revolutionized our knowledge of microbial diversity, little is known about the dynamic emergent phenotypes that arise within the context of mixed-species populations, which are not fully predicted using sequencing technologies alone. The International Space Station (ISS) is an isolated, closed human habitat that can be harnessed for cross-sectional and longitudinal functional microbiome studies. Using NASA-archived microbial isolates collected from the ISS potable water system over several years, we profiled five phenotypes: antibiotic resistance, metabolism, hemolysis, and biofilm structure/composition of individual or multispecies communities, which represent characteristics that could negatively impact astronaut health and life-support systems. Data revealed a temporal dependence on interactive behaviors, suggesting possible microbial adaptation over time within the ecosystem. This study represents one of the most extensive phenotypic characterization of ISS potable water microbiota with implications for microbial risk assessments of water systems in built environments in space and on Earth.

White Rann of Kachchh harbours distinct microbial diversity reflecting its unique biogeography

The understanding of sub-surface soil microbial diversity is limited at both saline and hypersaline ecosystems, even though salinity is found to affect the microbial community in aqueous and terrestrial environment. In this study, a phylo-taxonomy analysis as well as the functional characteristics of microbial community of flat salt basin of White Rann of Kachchh (WR), Gujarat, India was performed along the natural salinity gradient. The high throughput sequencing approach has revealed the numerical abundance of bacteria relative to the archaea. Salinity, TOC, EC and sulphate concentration might be the primary driver of the community distribution along the transect at WR. The much anticipated effect of salinity gradient on the microbial composition surprisingly turned out to be more speculative, with little variance in the community composition along the spatial distance of WR. The metabolic pathways involved in energy metabolism (like carbon, nitrogen, sulphur) along with environmental adaptive genes (like osmotic and oxidative stress response, heat and cold shock genes clusters) were abundantly annotated from shot-gun metagenomic study. The carbonic anhydrase harbouring bacteria Bacillus sp. DM4CA1 was isolated from WR, having a catalytic ability for converting the gaseous carbon dioxide in presence of calcium carbonate into calcite at 25 % higher rate as compared to non-harbouring strains. The enzyme has a role in multiple alternative pathways in microbial metabolism. With the array of results obtained, the study could become the new reference for understanding the diversity structure and functional characteristics of the microbial community of terrestrial saline environment.

Investigating alterations in the cellular envelope of Staphylococcus aureus in simulated microgravity using a random positioning machine

Continuous rotation of liquid bacterial culture in random positioning machine (RPM) causes formation of a colloidal bacterial culture in the culture tube, due to lack of sedimentation and convection. Interestingly, similar colloidal bacterial cultures can also be seen in suspended bacterial cultures in a spaceflight environment. Thus, as a consequence of no sedimentation, an alteration in the microenvironment of each bacterial cell in simulated microgravity is introduced, compared to the bacterial culture grown in normal gravity wherein they sediment slowly at the bottom of the culture tube. Apparently, a bacterial cell can sense changes in its environment through various receptors and sensors present at its surface, thus it can be speculated that this change in its microenvironment might induce changes in its cell wall and cell surface properties. In our study, changes in growth kinetics, cell wall constitution using FTIR (Fourier Transform Infrared Spectroscopy), cell surface hydrophobicity, autoaggregation ability and antibiotic susceptibility of Staphylococcus aureus NCIM 2079 strain, in simulated microgravity (using RPM) was studied in detail. Noteworthy alterations in its growth kinetics, cell wall constitution, cell surface hydrophobicity, autoaggregation ability and antibiotic susceptibility especially to Erythromycin and Clindamycin were observed. Our data suggests that microgravity may cause alterations in the cellular envelope of planktonic S.aureus cultures.

Use of Photobioreactors in Regenerative Life Support Systems for Human Space Exploration

There are still many challenges to overcome for human space exploration beyond low Earth orbit (LEO) (e.g., to the Moon) and for long-term missions (e.g., to Mars). One of the biggest problems is the reliable air, water and food supply for the crew. Bioregenerative life support systems (BLSS) aim to overcome these challenges using bioreactors for waste treatment, air and water revitalization as well as food production. In this review we focus on the microbial photosynthetic bioprocess and photobioreactors in space, which allow removal of toxic carbon dioxide (CO2) and production of oxygen (O2) and edible biomass. This paper gives an overview of the conducted space experiments in LEO with photobioreactors and the precursor work (on ground and in space) for BLSS projects over the last 30 years. We discuss the different hardware approaches as well as the organisms tested for these bioreactors. Even though a lot of experiments showed successful biological air revitalization on ground, the transfer to the space environment is far from trivial. For example, gas-liquid transfer phenomena are different under microgravity conditions which inevitably can affect the cultivation process and the oxygen production. In this review, we also highlight the missing expertise in this research field to pave the way for future space photobioreactor development and we point to future experiments needed to master the challenge of a fully functional BLSS.

The effects of combined environmental factors on the intestinal flora of mice based on ground simulation experiments

The composition and function of intestinal microbial communities are important for human health. However, these intestinal floras are sensitive to changes in the environment. Adverse changes to intestinal flora can affect the health of astronauts, resulting in difficulties in implementing space missions. We randomly divided mice into three groups and placed each group in either a normal environment, simulated microgravity environment or a combined effects environment, which included simulated microgravity, low pressure and noise. Fecal samples of the mice were collected for follow-up analysis based on metagenomics technology. With the influence of different space environmental factors, the species composition at the phylum and genus levels were significantly affected by the combined effects environment, especially the abundance of the Firmicutes and Bacteroidetes. Furthermore, screening was conducted to identify biomarkers that could be regarded as environmental markers. And there have also been some noticeable changes in the function of intestinal floras. Moreover, the abundance of antibiotic resistance genes (ARGs) was also found to be changed under different environmental conditions, such as bacitracin and vancomycin. The combined effects environment could significantly affect the species composition, function, and the expression of ARGs of intestinal flora of mice which may provide a theoretical basis for space medical supervision and healthcare.

Advances in space microbiology

Microbial research in space is being conducted for almost 50 years now. The closed system of the International Space Station (ISS) has acted as a microbial observatory for the past 10 years, conducting research on adaptation and survivability of microorganisms exposed to space conditions. This adaptation can be either beneficial or detrimental to crew members and spacecraft. Therefore, it becomes crucial to identify the impact of two primary stress conditions, namely, radiation and microgravity, on microbial life aboard the ISS. Elucidating the mechanistic basis of microbial adaptation to space conditions aids in the development of countermeasures against their potentially detrimental effects and allows us to harness their biotechnologically important properties. Several microbial processes have been studied, either in spaceflight or using devices that can simulate space conditions. However, at present, research is limited to only a few microorganisms, and extensive research on biotechnologically important microorganisms is required to make long-term space missions self-sustainable.

Survival of desert algae Chlorella exposed to Mars-like near space environment

Desert was considered terrestrial analogues of Mars. In this study, dried cells of desert green algae Chlorella were exposed to Mars-like near-space environment using high-altitude scientific balloons. We found that while a majority of Chlorella cells survived, they exhibited considerable damage, such as low photosynthetic activity, reduced cell growth, increased cell mortality rate, and altered chloroplast and mitochondrial ultrastructure. Additionally, transcriptome analysis of near space-exposed Chlorella cells revealed 3292 differentially expressed genes compared to cells in the control ground group, including heat shock proteins, antioxidant enzymes, DNA repair systems, as well as proteins related to the PSII apparatus and ribosomes. These data shed light on the possible survival strategy of desert algae to near space environments. Our results indicated that Mars-like near space conditions represent an extreme environment for desert algae in terms of temperature, pressure, and radiations. The survival strategy of Chlorella in response to near space will help gain insights into the possibility of extremophile colonization on the surface of Mars and in similar extraterrestrial habitats.

Revival of Anhydrobiotic Cyanobacterium Biofilms Exposed to Space Vacuum and Prolonged Dryness: Implications for Future Missions beyond Low Earth Orbit

Dried biofilms of Chroococcidiopsis sp. CCMEE 029 were revived after a 672-day exposure to space vacuum outside the International Space Station during the EXPOSE-R2 space mission. After retrieval, they were air-dried stored for 3.5 years. Space vacuum reduced cell viability and increased DNA damage compared to air-dried storage for 6 years under laboratory conditions. Long exposure times to space vacuum and extreme dryness decrease the changes of survival that ultimately depend on DNA damage repair upon rehydration, and hence, an in silico analysis of Chroococcidiopsis sp. CCMEE 029's genome was performed with a focus on DNA repair pathways. The analysis identified a high number of genes that encode proteins of the homologous recombination RecF pathway and base excision repair that were over-expressed during 1 and 6 h rehydration of space-vacuum exposed biofilms. This suggests that Chroococcidiopsis developed a survival strategy against desiccation, with DNA repair playing a key role, which allowed the revival of biofilms exposed to space vacuum. Unravelling how long anhydrobiotic cyanobacteria can persist under space vacuum followed by prolonged air-dried storage is relevant to future astrobiological experiments that use space platforms and might require prolonged air-dried storage of the exposed samples before retrieval to Earth.

Microbially-Enhanced Vanadium Mining and Bioremediation Under Micro- and Mars Gravity on the International Space Station

As humans explore and settle in space, they will need to mine elements to support industries such as manufacturing and construction. In preparation for the establishment of permanent human settlements across the Solar System, we conducted the ESA BioRock experiment on board the International Space Station to investigate whether biological mining could be accomplished under extraterrestrial gravity conditions. We tested the hypothesis that the gravity (g) level influenced the efficacy with which biomining could be achieved from basalt, an abundant material on the Moon and Mars, by quantifying bioleaching by three different microorganisms under microgravity, simulated Mars and Earth gravitational conditions. One element of interest in mining is vanadium (V), which is added to steel to fabricate high strength, corrosion-resistant structural materials for buildings, transportation, tools and other applications. The results showed that Sphingomonas desiccabilis and Bacillus subtilis enhanced the leaching of vanadium under the three gravity conditions compared to sterile controls by 184.92 to 283.22%, respectively. Gravity did not have a significant effect on mean leaching, thus showing the potential for biomining on Solar System objects with diverse gravitational conditions. Our results demonstrate the potential to use microorganisms to conduct elemental mining and other bioindustrial processes in space locations with non-1 × g gravity. These same principles apply to extraterrestrial bioremediation and elemental recycling beyond Earth.

Stability of Antimicrobial Drug Molecules in Different Gravitational and Radiation Conditions in View of Applications during Outer Space Missions

The evolution of different antimicrobial drugs in terrestrial, microgravity and hypergravity conditions is presented within this review, in connection with their implementation during human space exploration. Drug stability is of utmost importance for applications in outer space. Instabilities may be radiation-induced or micro-/hypergravity produced. The antimicrobial agents used in space may have diminished effects not only due to the microgravity-induced weakened immune response of astronauts, but also due to the gravity and radiation-altered pathogens. In this context, the paper provides schemes and procedures to find reliable ways of fighting multiple drug resistance acquired by microorganisms. It shows that the role of multipurpose medicines modified at the molecular scale by optical methods in long-term space missions should be considered in more detail. Solutions to maintain drug stability, even in extreme environmental conditions, are also discussed, such as those that would be encountered during long-duration space exploratory missions. While the microgravity conditions may not be avoided in space, the suggested approaches deal with the radiation-induced modifications in humans, bacteria and medicines onboard, which may be fought by novel pharmaceutical formulation strategies along with radioprotective packaging and storage.

Microbial Pathogenicity in Space

After a less dynamic period, space exploration is now booming. There has been a sharp increase in the number of current missions and also of those being planned for the near future. Microorganisms will be an inevitable component of these missions, mostly because they hitchhike, either attached to space technology, like spaceships or spacesuits, to organic matter and even to us (human microbiome), or to other life forms we carry on our missions. Basically, we never travel alone. Therefore, we need to have a clear understanding of how dangerous our "travel buddies" can be; given that, during space missions, our access to medical assistance and medical drugs will be very limited. Do we explore space together with pathogenic microorganisms? Do our hitchhikers adapt to the space conditions, as well as we do? Do they become pathogenic during that adaptation process? The current review intends to better clarify these questions in order to facilitate future activities in space. More technological advances are needed to guarantee the success of all missions and assure the reduction of any possible health and environmental risks for the astronauts and for the locations being explored.

Polyhydroxyalkanoates from extremophiles: A review

Polyhydroxyalkanoates (PHAs) are group monomers/heteropolymers that are biodegradable and widely used in biomedical applications. They are considered as alternatives to fossil derived polymers and accumulated by microbes including extremophilic archaea as energy storage inclusions under nutrient limitations. The use of extremophilic archaea for PHA production is an economically viable option for conventional aerobic processes, but less is known about their pathways and PHA accumulation capacities. This review summarized: (a) specific adaptive mechanisms towards extreme environments by extremophiles and specific role of PHAs; (b) understanding of PHA synthesis/metabolism in archaea and specific functional genes; (c) genetic engineering and process engineering approaches required for high-rate PHA production using extremophilic archaea. To conclude, the future studies are suggested to understand the membrane lipids and PHAs accumulation to explain the adaptation mechanism of extremophiles and exploiting it for commercial production of PHAs.

The Biological Study of Lifeless Worlds and Environments

Astrobiology is focused on the study of life in the universe. However, lifeless planetary environments yield biological information on the variety of ways in which physical and chemical conditions in the universe preclude the possibility of the origin or persistence of life, and in turn this will help explain the distribution and abundance of life, or lack of it, in the universe. Furthermore, many places that humans wish to explore and settle in space are lifeless, and studying the fate of life in these environments will aid our own success in thriving in them. In this synthetic review, I have three objectives, as follows: (1) To discuss the biological value and use of lifeless environments, (2) To explore the diverse planetary bodies and environments that can be lifeless and to categorize them, and (3) To propose sets of biological experiments that can be undertaken in different categories of lifeless worlds and environments and suggest concepts for mission ideas to realize these goals. They include origin of life and microbial inoculation experiments in lifeless but habitable environments. I suggest that the biological study of lifelessness is an underappreciated area in planetary sciences.

Role of Phage Capsid in the Resistance to UV-C Radiations

The conformational variation of the viral capsid structure plays an essential role both for the environmental resistance and acid nuclear release during cellular infection. The aim of this study was to evaluate how capsid rearrangement in engineered phages of M13 protects viral DNA and peptide bonds from damage induced by UV-C radiation. From in silico 3D modelling analysis, two M13 engineered phage clones, namely P9b and 12III1, were chosen for (i) chemical features of amino acids sequences, (ii) rearrangements in the secondary structure of their pVIII proteins and (iii) in turn the interactions involved in phage capsid. Then, their resistance to UV-C radiation and hydrogen peroxide (H2O2) was compared to M13 wild-type vector (pC89) without peptide insert. Results showed that both the phage clones acquired an advantage against direct radiation damage, due to a reorganization of interactions in the capsid for an increase of H-bond and steric interactions. However, only P9b had an increase in resistance against H2O2. These results could help to understand the molecular mechanisms involved in the stability of new virus variants, also providing quick and necessary information to develop effective protocols in the virus inactivation for human activities, such as safety foods and animal-derived materials.

Evaluating the effect of spaceflight on the host-pathogen interaction between human intestinal epithelial cells and Salmonella Typhimurium

Spaceflight uniquely alters the physiology of both human cells and microbial pathogens, stimulating cellular and molecular changes directly relevant to infectious disease. However, the influence of this environment on host-pathogen interactions remains poorly understood. Here we report our results from the STL-IMMUNE study flown aboard Space Shuttle mission STS-131, which investigated multi-omic responses (transcriptomic, proteomic) of human intestinal epithelial cells to infection with Salmonella Typhimurium when both host and pathogen were simultaneously exposed to spaceflight. To our knowledge, this was the first in-flight infection and dual RNA-seq analysis using human cells.

Modeled microgravity alters lipopolysaccharide and outer membrane vesicle production of the beneficial symbiont Vibrio fischeri

Reduced gravity, or microgravity, can have a pronounced impact on the physiology of animals, but the effects on their associated microbiomes are not well understood. Here, the impact of modeled microgravity on the shedding of Gram-negative lipopolysaccharides (LPS) by the symbiotic bacterium Vibrio fischeri was examined using high-aspect ratio vessels. LPS from V. fischeri is known to induce developmental apoptosis within its symbiotic tissues, which is accelerated under modeled microgravity conditions. In this study, we provide evidence that exposure to modeled microgravity increases the amount of LPS released by the bacterial symbiont in vitro. The higher rates of shedding under modeled microgravity conditions are associated with increased production of outer-membrane vesicles (OMV), which has been previously correlated to flagellar motility. Mutants of V. fischeri defective in the production and rotation of their flagella show significant decreases in LPS shedding in all treatments, but levels of LPS are higher under modeled microgravity despite loss of motility. Modeled microgravity also appears to affect the outer-membrane integrity of V. fischeri, as cells incubated under modeled microgravity conditions are more susceptible to cell-membrane-disrupting agents. These results suggest that, like their animal hosts, the physiology of symbiotic microbes can be altered under microgravity-like conditions, which may have important implications for host health during spaceflight.

MARSBOx: Fungal and Bacterial Endurance From a Balloon-Flown Analog Mission in the Stratosphere

Whether terrestrial life can withstand the martian environment is of paramount interest for planetary protection measures and space exploration. To understand microbial survival potential in Mars-like conditions, several fungal and bacterial samples were launched in September 2019 on a large NASA scientific balloon flight to the middle stratosphere (∼38 km altitude) where radiation levels resembled values at the equatorial Mars surface. Fungal spores of Aspergillus niger and bacterial cells of Salinisphaera shabanensis, Staphylococcus capitis subsp. capitis, and Buttiauxella sp. MASE-IM-9 were launched inside the MARSBOx (Microbes in Atmosphere for Radiation, Survival, and Biological Outcomes Experiment) payload filled with an artificial martian atmosphere and pressure throughout the mission profile. The dried microorganisms were either exposed to full UV-VIS radiation (UV dose = 1148 kJ m-2) or were shielded from radiation. After the 5-h stratospheric exposure, samples were assayed for survival and metabolic changes. Spores from the fungus A. niger and cells from the Gram-(-) bacterium S. shabanensis were the most resistant with a 2- and 4-log reduction, respectively. Exposed Buttiauxella sp. MASE-IM-9 was completely inactivated (both with and without UV exposure) and S. capitis subsp. capitis only survived the UV shielded experimental condition (3-log reduction). Our results underscore a wide variation in survival phenotypes of spacecraft associated microorganisms and support the hypothesis that pigmented fungi may be resistant to the martian surface if inadvertently delivered by spacecraft missions.

The influence of spaceflight and simulated microgravity on bacterial motility and chemotaxis

As interest in space exploration rises, there is a growing need to quantify the impact of microgravity on the growth, survival, and adaptation of microorganisms, including those responsible for astronaut illness. Motility is a key microbial behavior that plays important roles in nutrient assimilation, tissue localization and invasion, pathogenicity, biofilm formation, and ultimately survival. Very few studies have specifically looked at the effects of microgravity on the phenotypes of microbial motility. However, genomic and transcriptomic studies give a broad general picture of overall gene expression that can be used to predict motility phenotypes based upon selected genes, such as those responsible for flagellar synthesis and function and/or taxis. In this review, we focus on specific strains of Gram-negative bacteria that have been the most studied in this context. We begin with a discussion of Earth-based microgravity simulation systems and how they may affect the genes and phenotypes of interest. We then summarize results from both Earth- and space-based systems showing effects of microgravity on motility-related genes and phenotypes.

Shotgun metagenomic analysis of kombucha mutualistic community exposed to Mars-like environment outside the International Space Station

Kombucha is a multispecies microbial ecosystem mainly composed of acetic acid bacteria and osmophilic acid-tolerant yeasts, which is used to produce a probiotic drink. Furthermore, Kombucha Mutualistic Community (KMC) has been recently proposed to be used during long space missions as both a living functional fermented product to improve astronauts' health and an efficient source of bacterial nanocellulose. In this study, we compared KMC structure and functions before and after samples were exposed to the space/Mars-like environment outside the International Space Station in order to investigate the changes related to their re-adaptation to Earth-like conditions by shotgun metagenomics, using both diversity and functional analyses of Community Ecology and Complex Networks approach. Our study revealed that the long-term exposure to space/Mars-like conditions on low Earth orbit may disorganize the KMC to such extent that it will not restore the initial community structure; however, KMC core microorganisms of the community were maintained. Nonetheless, there were no significant differences in the community functions, meaning that the KMC communities are ecologically resilient. Therefore, despite the extremely harsh conditions, key KMC species revived and provided the community with the genetic background needed to survive long periods of time under extraterrestrial conditions.

Microbiome dynamics during the HI-SEAS IV mission, and implications for future crewed missions beyond Earth

BACKGROUND

Human health is closely interconnected with its microbiome. Resilient microbiomes in, on, and around the human body will be key for safe and successful long-term space travel. However, longitudinal dynamics of microbiomes inside confined built environments are still poorly understood. Herein, we used the Hawaii Space Exploration Analog and Simulation IV (HI-SEAS IV) mission, a 1 year-long isolation study, to investigate microbial transfer between crew and habitat, in order to understand adverse developments which may occur in a future outpost on the Moon or Mars.

RESULTS

Longitudinal 16S rRNA gene profiles, as well as quantitative observations, revealed significant differences in microbial diversity, abundance, and composition between samples of the built environment and its crew. The microbiome composition and diversity associated with abiotic surfaces was found to be rather stable, whereas the microbial skin profiles of individual crew members were highly dynamic, resulting in an increased microbiome diversity at the end of the isolation period. The skin microbiome dynamics were especially pronounced by a regular transfer of the indicator species Methanobrevibacter between crew members within the first 200 days. Quantitative information was used to track the propagation of antimicrobial resistance in the habitat. Together with functional and phenotypic predictions, quantitative and qualitative data supported the observation of a delayed longitudinal microbial homogenization between crew and habitat surfaces which was mainly caused by a malfunctioning sanitary facility.

CONCLUSIONS

This study highlights main routes of microbial transfer, interaction of the crew, and origins of microbial dynamics in an isolated environment. We identify key targets of microbial monitoring, and emphasize the need for defined baselines of microbiome diversity and abundance on surfaces and crew skin. Targeted manipulation to counteract adverse developments of the microbiome could be a highly important strategy to ensure safety during future space endeavors. Video abstract.

Mechanotransduction in Prokaryotes: A Possible Mechanism of Spaceflight Adaptation

Our understanding of the mechanisms of microgravity perception and response in prokaryotes (Bacteria and Archaea) lag behind those which have been elucidated in eukaryotic organisms. In this hypothesis paper, we: (i) review how eukaryotic cells sense and respond to microgravity using various pathways responsive to unloading of mechanical stress; (ii) we observe that prokaryotic cells possess many structures analogous to mechanosensitive structures in eukaryotes; (iii) we review current evidence indicating that prokaryotes also possess active mechanosensing and mechanotransduction mechanisms; and (iv) we propose a complete mechanotransduction model including mechanisms by which mechanical signals may be transduced to the gene expression apparatus through alterations in bacterial nucleoid architecture, DNA supercoiling, and epigenetic pathways.

Advantages and Limitations of Current Microgravity Platforms for Space Biology Research

Human Space exploration has created new challenges and new opportunities for science. Reaching beyond the Earth’s surface has raised the issue of the importance of gravity for the development and the physiology of biological systems, while giving scientists the tools to study the mechanisms of response and adaptation to the microgravity environment. As life has evolved under the constant influence of gravity, gravity affects biological systems at a very fundamental level. Owing to limited access to spaceflight platforms, scientists rely heavily on on-ground facilities that reproduce, to a different extent, microgravity or its effects. However, the technical constraints of counterbalancing the gravitational force on Earth add complexity to data interpretation. In-flight experiments are also not without their challenges, including additional stressors, such as cosmic radiation and lack of convection. It is thus extremely important in Space biology to design experiments in a way that maximizes the scientific return and takes into consideration all the variables of the chosen setup, both on-ground or on orbit. This review provides a critical analysis of current ground-based and spaceflight facilities. In particular, the focus was given to experimental design to offer the reader the tools to select the appropriate setup and to appropriately interpret the results.

Falling bacterial communities from the atmosphere

BACKGROUND

Bacteria emitted into the atmosphere eventually settle to the pedosphere via sedimentation (dry deposition) or precipitation (wet deposition), constituting a part of the global cycling of substances on Earth, including the water cycle. In this study, we aim to investigate the taxonomic compositions and flux densities of bacterial deposition, for which little is known regarding the relative contributions of each mode of atmospheric deposition, the taxonomic structures and memberships, and the aerodynamic properties in the atmosphere.

RESULTS

Precipitation was found to dominate atmospheric bacterial deposition, contributing to 95% of the total flux density at our sampling site in Korea, while bacterial communities in precipitation were significantly different from those in sedimentation, in terms of both their structures and memberships. Large aerodynamic diameters of atmospheric bacteria were observed, with an annual mean of 8.84 μm, which appears to be related to their large sedimentation velocities, with an annual mean of 1.72 cm s^- 1 for all bacterial taxa combined. The observed mean sedimentation velocity for atmospheric bacteria was larger than the previously reported mean sedimentation velocities for fungi and plants.

CONCLUSIONS

Large aerodynamic diameters of atmospheric bacteria, which are likely due to the aggregation and/or attachment to other larger particles, are thought to contribute to large sedimentation velocities, high efficiencies as cloud nuclei, and large amounts of precipitation of atmospheric bacteria. Moreover, the different microbiotas between precipitation and sedimentation might indicate specific bacterial involvement and/or selective bacterial growth in clouds. Overall, our findings add novel insight into how bacteria participate in atmospheric processes and material circulations, including hydrological circulation, on Earth.

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.

A Cruise-Phase Microbial Survival Model for Calculating Bioburden Reductions on Past or Future Spacecraft Throughout Their Missions with Application to Europa Clipper

During transit between the Earth and planetary destinations, spacecraft encounter conditions that are deleterious to the survival of terrestrial microorganisms. To model the resulting bioburden reduction, a Cruise-Phase Microbial Survival (CPMS) model was prepared based upon the Lunar Microbial Survival model, which considers the effects of temperature, vacuum, ultraviolet (UV), and ionizing radiation found in the space environment. As an example, the CPMS was used to determine the expected bioburden reductions on the Europa Clipper spacecraft upon arrival at Jupiter under two different transit scenarios. Under a direct trajectory scenario, exterior surfaces are rapidly sterilized with tens of thousands of lethal doses (LDs) absorbed to the spacecraft exterior and at least one LD to all interior spaces of the spacecraft heated to at least 240 K. Under a Venus-Earth-Earth gravity assist (VEEGA) trajectory, we find substantially higher bioburden reductions resulting from the spacecraft spending much more time near the Sun and more time in transit overall. With VEEGA, the exterior absorbs hundreds of thousands of LDs and interior surfaces heated above 230 K would absorb at least one LD. From these simulations, we are able to generalize about bioburden reduction in transit on spacecraft in general, finding that all spacecraft surfaces would sustain at least one LD in ≤38.5 years even if completely unheated. Temperature and vacuum synergy dominates surface reductions out to at most 3.3 AU (for gold multilayer insulation), UV irradiation and temperature between 3.3 and 600 AU, and past 600 AU the effect of vacuum acting alone is the primary factor for all exterior and interior surfaces. Even under the most conservative estimates, if the average interior temperature of the Cassini spacecraft exceeded 218 K, or the Galileo spacecraft interior exceeded 222 K, neither spacecraft would have likely had any viable bioburdens onboard at disposal.

Comparisons of Transcriptome Profiles from Bacillus subtilis Cells Grown in Space versus High Aspect Ratio Vessel (HARV) Clinostats Reveal a Low Degree of Concordance

Although clinostats have long been used in space microbiology studies as ground-based analogs of spaceflight, few studies to date have systematically compared -omics data from clinostats versus spaceflight. This study compared the transcriptomic response of the Gram-positive bacterium Bacillus subtilis flown in space with corresponding transcriptomes derived from 2-D clinostat (High Aspect Ratio Vessel: HARV) experiments performed under the same conditions of bacterial strain, growth medium, temperature, and incubation time. High-quality total RNA (RNA Integrity Number >9.6) was isolated from multiple biological replicates from each treatment, transcripts were quantified by RNA-seq, and raw data was processed through a previously described standardized bioinformatics pipeline. Transcriptome data sets from spaceflight-grown and corresponding clinostat-grown cells were compared by using three different methods: (i) principal component analysis, (ii) analysis of differentially expressed genes, and (iii) gene set enrichment analysis of KEGG pathways. All three analyses found a low degree of concordance between the spaceflight and corresponding clinostat transcriptome data sets, ranging from 0.9% to 5.3% concordance. These results are in agreement with prior studies that also revealed low concordances between spaceflight and clinostat transcriptomes of the Gram-negative bacteria Rhodospirillum rubrum and Pseudomonas aeruginosa. The results are discussed from the perspective of several potential confounding factors, and suggestions are offered with the aim of achieving increased concordance between clinostat and spaceflight data.