Soilless cultivation of soybean for Bioregenerative Life-Support Systems: a literature review and the experience of the MELiSSA Project - Food characterisation Phase I

Protein plant factories: production and resource use efficiency of soybean proteins in vertical farming

BACKGROUND

Controlled environment agriculture, particularly vertical farms (VF), also called plant factories, is often claimed as a solution for global food security due to its ability to produce crops unaffected by weather or pests. In principle, essential macronutrients of the human diet, like protein, could technically be produced in VF. This aspect becomes relevant in the era of protein transition, marked by an increasing consumer interest in plant-based protein and environmental challenges faced by conventional farming. However, the real question is: what does the cultivation of protein crops in VF imply in terms of resource use? To address this, a study was conducted using a VF experiment focusing on two soybean cultivars.

RESULTS

With a variable plant density to optimize area use, and because of the ability to have more crop cycles per year, protein yield per square metre of crop was about eight times higher than in the open field. Assuming soy as the only protein source in the diet, the resources needed to get total yearly protein requirement of a reference adult would be 20 m2 of crop area, 2.4 m3 of water and 16 MWh of electricity, versus 164 m2, 111 m3 and 0.009 MWh in the field.

CONCLUSIONS

The study's results inform the debate on protein production and the efficiency of VF compared to conventional methods. With current electricity prices, it is unlikely to justify production of simple protein crops in VF or promote it as a solution to meet global protein needs. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Phosphorus-solubilizing bacteria improve the growth of Nicotiana benthamiana on lunar regolith simulant by dissociating insoluble inorganic phosphorus

In-situ utilization of lunar soil resources will effectively improve the self-sufficiency of bioregenerative life support systems for future lunar bases. Therefore, we have explored the microbiological method to transform lunar soil into a substrate for plant cultivation. In this study, five species of phosphorus-solubilizing bacteria are used as test strains, and a 21-day bio-improving experiment with another 24-day Nicotiana benthamiana cultivation experiment are carried out on lunar regolith simulant. We have observed that the phosphorus-solublizing bacteria Bacillus mucilaginosus, Bacillus megaterium, and Pseudomonas fluorescens can tolerate the lunar regolith simulant conditions and dissociate the insoluble phosphorus from the regolith simulant. The phosphorus-solubilizing bacteria treatment improves the available phosphorus content of the regolith simulant, promoting the growth of Nicotiana benthamiana. Here we demonstrate that the phosphorus-solubilizing bacteria can effectively improve the fertility of lunar regolith simulant, making it a good cultivation substrate for higher plants. The results can lay a technical foundation for plant cultivation based on lunar regolith resources in future lunar bases.

Utility of Urine: From Antiquity to the Moon

In ancient times, religious traditions considered urine a useful distilled product from the body. It has been used as a form of medicinal therapy for many years and is still used by millions of people worldwide who drink their urine for therapeutic purposes. The positive effects of urine on health were reported since the Renaissance for its bactericidal effects on wounds, healing effects on gastric ulcers, improved protein synthesis, regression of liver tumors, and ability to block the growth of tuberculosis mycobacteria. Urine contains a large number of chemical agents, some of which have already been identified, although others are still unknown. It is important to identify these agents through new technological methods, such as mass spectrometry, as new biomarkers of diseases. Recently, the use of urine has been discovered as a "green" element to produce electricity, agriculture fertilizers, generation of water, and building material for lunar bases for future space explorations.

Carbonate precipitation and nitrogen fixation in AMG (Artificial Martian Ground) by cyanobacteria

This article describes experiments performed to study the survival, growth, specific adaptations and bioremediation potential of certain extreme cyanobacteria strains within a simulation of the atmospheric composition, temperature and pressure expected in a future Martian greenhouse. Initial species have been obtained from Mars-analogue sites in Georgia. The results clearly demonstrate that specific biochemical adaptations allow these autotrophs to metabolize within AMG (Artificial Martian Ground) and accumulate biogenic carbon and nitrogen. These findings may thus contribute to the development of future Martian agriculture, as well as other aspects of the life-support systems at habitable Mars stations. The study shows that carbonate precipitation and nitrogen fixation, performed by cyanobacterial communities thriving within the simulated Martian greenhouse conditions, are cross-linked biological processes. At the same time, the presence of the perchlorates (at low concentrations) in the Martian ground may serve as the initial source of oxygen and, indirectly, hydrogen via photo-Fenton reactions. Various carbonates, ammonium and nitrate salts were obtained as the result of these experiments. These affect the pH, salinity and solubility of the AMG and its components, and so the AMG's scanty biogenic properties improved, which is essential for the sustainable growth of the agricultural crops. Therefore, the use of microorganisms for the biological remediation and continuous in situ fertilization of Artificial Martian Ground is possible.

Can Peat Amendment of Mars Regolith Simulant Allow Soybean Cultivation in Mars Bioregenerative Life Support Systems?

Higher plants will play a key role in human survival in Space, being able to regenerate resources and produce fresh food. However, the creation of a fertile substrate based on extra-terrestrial soils is still a challenge for space cultivation. We evaluated the adaptability of soybean (Glycine max (L.) Merr.) cultivar 'Pr91M10' to three substrates, the Mojave Mars regolith Simulant MMS-1, alone (R100), and in a mixture with blond sphagnum peat at two different volumes, 85:15 (R85P15) and 70:30 (R70P30), in plants directly sown on the substrates or transplanted after sowing on peat. The low pH of peat (4.34) allowed the mitigation of the alkalinity of the Mars regolith simulant (pH 8.86), lowering the initial pH to neutral (6.98, R85P15), or subacid to neutral (6.33, R70P30) values. Seed germination reached the highest percentage in the shortest time in the mixture of regolith simulant with 15% of peat. The cultivation substrate did not affect the plant growth and nutritional status. However, a significant interaction between the substrate and planting method was found in several growth parameters, with the highest positive effects observed in plants resulting from direct sowing on the regolith mixture with peat.

Metaproteomics, Heterotrophic Growth, and Distribution of Nitrosomonas europaea and Nitrobacter winogradskyi after Long-Term Operation of an Autotrophic Nitrifying Biofilm Reactor

Bioregenerative life support systems (BLSS) are currently in development to tackle low recovery efficiencies, high energy demands, as well as food, water, and oxygen production challenges through the regeneration of nutrients from waste streams. The MELiSSA pilot plant has been developed as a testbed for regenerative life support system bioreactor operation and characterization. As nitrogen is a vital resource in such systems, we studied the functional composition of a new packed-bed nitrifying bioreactor inoculated with a co-culture of Nitrosomonas europaea (ATCC 25978) and Nitrobacter winogradskyi (ATCC 25391). After 840 days of autotrophic continuous cultivation, the packed-bed was sampled at five vertical positions, each with three horizontal positions, and the biomass at each position was characterized via qPCR, 16S amplicon sequencing, and liquid chromatography tandem mass spectrometry. The total number of cells within the different sections fluctuated around 8.95 ± 5.10 × 107 cells/mL of beads. Based on 16S amplicons and protein content, N. europaea and N. winogradskyi constituted overall 44.07 ± 11.75% and 57.53 ± 12.04% of the nitrifying bioreactor, respectively, indicating the presence of a heterotrophic population that, even after such a long operation time, did not affect the nitrification function of the bioreactor. In addition, DNA-based abundance estimates showed that N. europaea was slightly more abundant than N. winogradskyi, whereas protein-based abundance estimates indicated a much higher abundance of N. europaea. This highlights that single-method approaches need to be carefully interpreted in terms of overall cell abundance and metabolic activity.

A novel device to study altered gravity and light interactions in seedling tropisms

Long-duration space missions will need to rely on the use of plants in bio-regenerative life support systems (BLSSs) because these systems can produce fresh food and oxygen, reduce carbon dioxide levels, recycle metabolic waste, and purify water. In this scenario, the need for new experiments on the effects of altered gravity conditions on plant biological processes is increasing, and significant efforts should be devoted to new ideas aimed at increasing the scientific output and lowering the experimental costs. Here, we report the design of an easy-to-produce and inexpensive device conceived to analyze the effect of interaction between gravity and light on root tropisms. Each unit consisted of a polystyrene multi-slot rack with light-emitting diodes (LEDs), capable of holding Petri dishes and assembled with a particular filter-paper folding. The device was successfully used for the ROOTROPS (for root tropisms) experiment performed in the Large Diameter Centrifuge (LDC) and Random Positioning Machine (RPM) at ESA's European Space Research and Technology centre (ESTEC). During the experiments, four light treatments and six gravity conditions were factorially combined to study their effects on root orientation of Brassica oleracea seedlings. Light treatments (red, blue, and white) and a dark condition were tested under four hypergravity levels (20 g, 15 g, 10 g, 5 g), a 1 g control, and a simulated microgravity (RPM) condition. Results of validation tests showed that after 24 h, the assembled system remained unaltered, no slipping or displacement of seedlings occurred at any hypergravity treatment or on the RPM, and seedlings exhibited robust growth. Overall, the device was effective and reliable in achieving scientific goals, suggesting that it can be used for ground-based research on phototropism-gravitropism interactions. Moreover, the concepts developed can be further expanded for use in future spaceflight experiments with plants.

Conducting Plant Experiments in Space and on the Moon

The growth and development of plants during spaceflight have important implications for both basic and applied research supported by NASA and other international space agencies. While there have been many reviews of plant space biology, this chapter attempts to fill a gap in the literature on the actual process and methods of performing plant research in the spaceflight environment. One of the authors (JZK) has been a principal investigator on eight spaceflight projects. These experiences include using the U.S. Space Shuttle, the former Russian Space Station Mir, and the International Space Station, utilizing the Space Shuttle and Space X as launch vehicles. While there are several ways to fly an experiment into space and to obtain a spaceflight opportunity, this review focuses on using the NASA peer-reviewed sciences approach to get an experiment manifested for flight. Three narratives for the implementation of plant space biology experiments are considered from rapid turn around of a few months to a project with new hardware development that lasted 6 years. The many challenges of spaceflight research include logistical and resource constraints such as crew time, power, cold stowage, data downlinks, among others. Additional issues considered are working at NASA centers, hardware development, safety concerns, and the engineering versus science culture in space agencies. The difficulties of publishing the results from spaceflight research based on such factors as the lack of controls, limited sample size, and the indirect effects of the spaceflight environment also are summarized. Lessons learned from these spaceflight experiences are discussed in the context of improvements for future space-based research projects with plants. We also will consider new opportunities for Moon-based research via NASA's Artemis lunar exploration program.

Review of research into bioregenerative life support system(s) which can support humans living in space

To travel beyond the Earth and realize long-term survival in deep space, humans need to construct Bioregenerative Life Support System (BLSS), which reduces the requirement for supplies from the Earth by in situ regenerating oxygen, water and food needed by astronauts, and prevents pollution to extraterrestrial bodies by recycling waste. Since the 1960s, the USSR/Russia, the United States, Europe, Japan, and China carried out a number of studies with abundant achievements in BLSS systematic theories, plants/animals/microorganisms unit technologies, design/construction, and long-term operation/regulation. China's "Lunar Palace 365″ experiment realized Earth-based closed human survival for a year, with a material closure of >98%. However, a lot of research work is still needed to ultimately realize BLSS application in space, especially given the space experiment of BLSS never carried out, and the overall impact of space environment on BLSS unknown. Lunar exploration projects such as lunar village and lunar research station are successively proceeding. Therefore, future BLSS research will focus on lunar probe payload carrying experiments to study mechanisms of small uncrewed closed ecosystem in space and clarify the impact of space environmental conditions on the ecosystem, so as to correct the design and operation parameters of Earth-based BLSS. Such research will provide theoretical and technological support for BLSS application in crewed deep space exploration.

Comparative Analysis of the Effect of Carbon- and Titanium-Ions Irradiation on Morpho-Anatomical and Biochemical Traits of Dolichos melanophthalmus DC. Seedlings Aimed to Space Exploration

The realization of manned missions for space exploration requires the development of Bioregenerative Life Support Systems (BLSSs) to make human colonies self-sufficient in terms of resources. Indeed, in these systems, plants contribute to resource regeneration and food production. However, the cultivation of plants in space is influenced by ionizing radiation which can have positive, null, or negative effects on plant growth depending on intrinsic and environmental/cultivation factors. The aim of this study was to analyze the effect of high-LET (Linear Energy Transfer) ionizing radiation on seed germination and seedling development in eye bean. Dry seeds of Dolichos melanophthalmus DC. (eye bean) were irradiated with two doses (1 and 10 Gy) of C- and Ti-ions. Seedlings from irradiated seeds were compared with non-irradiated controls in terms of morpho-anatomical and biochemical traits. Results showed that the responses of eye bean plants to radiation are dose-specific and dependent on the type of ion. The information obtained from this study will be useful for evaluating the radio-resistance of eye bean seedlings, for their possible cultivation and utilization as food supplement in space environments.

Development of Nitrogen Recycling Strategies for Bioregenerative Life Support Systems in Space

To enable long-distance space travel, the development of a highly efficient and robust system to recover nutrients from waste streams is imperative. The inability of the current physicochemical-based environmental control and life support system (ECLSS) on the ISS to produce food in situ and to recover water and oxygen at high enough efficiencies results in the need for frequent resupply missions from Earth. Therefore, alternative strategies like biologically-based technologies called bioregenerative life support systems (BLSSs) are in development. These systems aim to combine biological and physicochemical processes, which enable in situ water, oxygen, and food production (through the highly efficient recovery of minerals from waste streams). Hence, minimalizing the need for external consumables. One of the BLSS initiatives is the European Space Agency's (ESA) Micro-Ecological Life Support System Alternative (MELiSSA). It has been designed as a five-compartment bioengineered system able to produce fresh food and oxygen and to recycle water. As such, it could sustain the needs of a human crew for long-term space exploration missions. A prerequisite for the self-sufficient nature of MELiSSA is the highly efficient recovery of valuable minerals from waste streams. The produced nutrients can be used as a fertilizer for food production. In this review, we discuss the need to shift from the ECLSS to a BLSS, provide a summary of past and current BLSS programs and their unique approaches to nitrogen recovery and processing of urine waste streams. In addition, compartment III of the MELiSSA loop, which is responsible for nitrogen recovery, is reviewed in-depth. Finally, past, current, and future related ground and space demonstration and the space-related challenges for this technology are considered.

The World Smallest Plants (Wolffia Sp.) as Potential Species for Bioregenerative Life Support Systems in Space

To colonise other planets, self-sufficiency of space missions is mandatory. To date, the most promising technology to support long-duration missions is the bioregenerative life support system (BLSS), in which plants as autotrophs play a crucial role in recycling wastes and producing food and oxygen. We reviewed the scientific literature on duckweed (Lemnaceae) and reported available information on plant biological traits, nutritional features, biomass production, and space applications, especially of the genus Wolffia. Results confirmed that the smallest existing higher plants are the best candidate for space BLSS. We discussed needs for further research before criticalities to be addressed to finalise the adoption of Wolffia species for space missions.

Biology and crop production in Space environments: Challenges and opportunities

Long-term manned space-exploration missions and the permanence of human colonies on orbital stations or planetary habitats will require the regeneration of resources onboard or in-situ. Bioregenerative Life Support Systems (BLSSs) are artificial environments where different compartments, involving both living organisms and physical-chemical processes, are integrated to achieve a safe, self-regulating, and chemically balanced Earth-like environment to support human life. Higher plants are key elements of such systems and Space greenhouses represent the producers' compartment. Growing plants in Space requires the knowledge of their growth responses not only to all environmental factors acting on Earth, but also to specific Space constraints such as altered gravity, ionizing radiations and confined volume. Moreover, cultivation techniques need to be adjusted considering such limitations. The type and intensity of environmental factors to be taken into account depend on the mission scenarios. Here, we summarize constraints and opportunities of cultivating higher plants in Space to regenerate resources and produce fresh food onboard. Both biological and agro-technological issues are considered briefly going through experiments both ground-based on Earth and in Space.

Subsequent inclusion/exclusion criteria to select the best species for an experiment performed on the ISS in a refurbished hardware

The interest in re-using flown hardware for new and different space biology experiments is increasing. To match the constraints of the flown hardware with the requirements of the new biological system, innovative methodological approaches are necessary. MULTITROP was a successful plant biology experiment that was performed on the ISS to investigate multiple-tropism interactions during the early stage of seedling growth. We used the hardware designed and flown for the IFOAM experiment in 2009. The main challenge was to implement seeds of a crop species in a growth chamber conceived for yeast culture and to grow the seedlings in microgravity condition but activating seed germination on ground before the launch. Our approach was to adapt the biological system to the hardware constraints and also to the experiment timing and the environmental factors expected during the prelaunch, launch and flight operations. We looked for an objective and repeatable method to effectively select the best suited species. Innovatively, we applied the method of inclusion/exclusion criteria to adapt a new biological system to a reused hardware. The list and the consecutive order of the specific inclusive/exclusive criteria turned out to be a valid support to guide the science team in objectively choosing the most suitable species for the experiment. Among the 50 initial food species, the carrot seeds resulted as the best in satisfying all technical requirements and post-flight data confirmed the expectations.

Light and Low Relative Humidity Increase Antioxidants Content in Mung Bean (Vigna radiata L.) Sprouts

In the last decades, there has been a growing interest in the production of sprouts, since they are a highly nutritious food, particularly suitable for indoor farming in urban areas. Achieving sprout production in indoor systems requires an understanding of possible alterations induced by the microclimate. The aim of this study was to analyze the combined effect of presence/absence of light and high/low air relative humidity (RH) on mung bean sprouts. Morpho-anatomical development and functional anatomical traits in hypocotyl were quantified. The content of antioxidants, soluble sugars, and starch were measured for nutritional and functional purposes. Different RH regimes mainly induced morpho-anatomical modifications, while the presence/absence of light changed the content of antioxidant compounds. Increments in stele diameter at high RH suggest a higher water uptake and conductivity, compared to the low RH treatment; low RH and light induced anatomical traits improving plant water transport (reduced number of cortical layers) and increased the production of antioxidants. The overall results suggested that RH and light, already at the early stages of development, affect the plant's nutritional value. Therefore, the combination of light and low RH allows the production of antioxidant-rich mung bean sprouts to be used as a food supplement.

Mars Regolith Simulant Ameliorated by Compost as in situ Cultivation Substrate Improves Lettuce Growth and Nutritional Aspects

Heavy payloads in future shuttle journeys to Mars present limiting factors, making self-sustenance essential for future colonies. Therefore, in situ resources utilization (ISRU) is the path to successful and feasible space voyages. This research frames the concept of planting leafy vegetables on Mars regolith simulant, ameliorating this substrate’s fertility by the addition of organic residues produced in situ. For this purpose, two butterhead lettuce (Lactuca sativa L. var. capitata) cultivars (green and red Salanova^®) were chosen to be cultivated in four different mixtures of MMS-1 Mojave Mars simulant:compost (0:100, 30:70, 70:30 and 100:0; v:v) in a phytotron open gas exchange growth chamber. The impact of compost rate on both crop performance and the nutritive value of green- and red-pigmented cultivars was assessed. The 30:70 mixture proved to be optimal in terms of crop performance, photosynthetic activity, intrinsic water use efficiency and quality traits of lettuce. In particular, red Salanova^® showed the best performance in terms of these quality traits, registering 32% more phenolic content in comparison to 100% simulant. Nonetheless, the 70:30 mixture represents a more realistic scenario when taking into consideration the sustainable use of compost as a limited resource in space farming, while still accepting a slight significant decline in yield and quality in comparison to the 30:70 mixture.

Suitability of Solanum lycopersicum L. 'Microtom' for growth in Bioregenerative Life Support Systems: exploring the effect of high-LET ionising radiation on photosynthesis, leaf structure and fruit traits

The realisation of manned space exploration requires the development of Bioregenerative Life Support Systems (BLSS). In such self-sufficient closed habitats, higher plants have a fundamental role in air regeneration, water recovery, food production and waste recycling. In the space environment, ionising radiation represents one of the main constraints to plant growth. In this study, we explore whether low doses of heavy ions, namely Ca 25 Gy, delivered at the seed stage, may induce positive outcomes on growth and functional traits in plants of Solanum lycopersicum L. 'Microtom'. After irradiation of seed, plant growth was monitored during the whole plant life cycle, from germination to fruit ripening. Morphological parameters, photosynthetic efficiency, leaf anatomical functional traits and antioxidant production in leaves and fruits were analysed. Our data demonstrate that irradiation of seeds with 25 Gy Ca ions does not prevent achievement of the seed-to-seed cycle in 'Microtom', and induces a more compact plant size compared to the control. Plants germinated from irradiated seeds show better photochemical efficiency than controls, likely due to the higher amount of D1 protein and photosynthetic pigment content. Leaves of these plants also had smaller cells with a lower number of chloroplasts. The dose of 25 Gy Ca ions is also responsible for positive outcomes in fruits: although developing a lower number of berries, plants germinated from irradiated seeds produce larger berries, richer in carotenoids, ascorbic acid and anthocyanins than controls. These specific traits may be useful for 'Microtom' cultivation in BLSS in space, in so far as the crew members could benefit from fresh food richer in functional compounds that can be directly produced on board.

Testing New Concepts for Crop Cultivation in Space: Effects of Rooting Volume and Nitrogen Availability

Long term human missions to the Moon and Mars, rely on life support systems for food production and regeneration of resources. In the EU H2020 TIME SCALE-project, an advanced life support system concept was developed to facilitate plant research and technology demonstration under different gravity conditions. Ground experiments assessed irrigation systems and effects of rooting- and nutrient solution volume. The maximal allowed volume for existing International Space Station research facilities (3.4 L) was able to support cultivation of two lettuce heads for at least 24 days. A smaller rooting volume (0.6 L) increased root biomass after 24 days, but induced a 5% reduction in total biomass at day 35. Regulating effects of nitrate supply on plant water fluxes in light and dark were also investigated. At low concentrations of nitrate in the nutrient solution, both transpiration and stomatal conductance increased rapidly with increasing nitrate concentration. During day-time this increase levelled off at high concentrations, while during nigh-time there was a distinct decline at supra optimal concentrations. Plants supplied with nitrate concentrations as low as 1.25 mM did not show visible signs of nutrient stress or growth reduction. These findings hold promise for both reducing the environmental impact of terrestrial horticulture and avoiding nutrient stress in small scale closed cultivation systems for space.

Comparative transcriptomics indicate changes in cell wall organization and stress response in seedlings during spaceflight

PREMISE OF THE STUDY

Plants will play an important role in the future of space exploration as part of bioregenerative life support. Thus, it is important to understand the effects of microgravity and spaceflight on gene expression in plant development.

METHODS

We analyzed the transcriptome of Arabidopsis thaliana using the Biological Research in Canisters (BRIC) hardware during Space Shuttle mission STS-131. The bioinformatics methods used included RMA (robust multi-array average), MAS5 (Microarray Suite 5.0), and PLIER (probe logarithmic intensity error estimation). Glycome profiling was used to analyze cell wall composition in the samples. In addition, our results were compared to those of two other groups using the same hardware on the same mission (BRIC-16).

KEY RESULTS

In our BRIC-16 experiments, we noted expression changes in genes involved in hypoxia and heat shock responses, DNA repair, and cell wall structure between spaceflight samples compared to the ground controls. In addition, glycome profiling supported our expression analyses in that there was a difference in cell wall components between ground control and spaceflight-grown plants. Comparing our studies to those of the other BRIC-16 experiments demonstrated that, even with the same hardware and similar biological materials, differences in results in gene expression were found among these spaceflight experiments.

CONCLUSIONS

A common theme from our BRIC-16 space experiments and those of the other two groups was the downregulation of water stress response genes in spaceflight. In addition, all three studies found differential regulation of genes associated with cell wall remodeling and stress responses between spaceflight-grown and ground control plants.

Changes in Leaf Anatomical Traits Enhanced Photosynthetic Activity of Soybean Grown in Hydroponics with Plant Growth-Promoting Microorganisms

The use of hydroponic systems for cultivation in controlled climatic conditions and the selection of suitable genotypes for the specific environment help improving crop growth and yield. We hypothesized that plant performance in hydroponics could be further maximized by exploiting the action of plant growth-promoting organisms (PGPMs). However, the effects of PGPMs on plant physiology have been scarcely investigated in hydroponics. Within a series of experiments aimed to identify the best protocol for hydroponic cultivation of soybean [Glycine max (L.) Merr.], we evaluated the effects of a PGPMs mix, containing bacteria, yeasts, mycorrhiza and trichoderma beneficial species on leaf anatomy, photosynthetic activity and plant growth of soybean cv. 'Pr91m10' in closed nutrient film technique (NFT). Plants were grown in a growth chamber under semi-aseptic conditions and inoculated at seed, seedling and plant stages, and compared to non-inoculated (control) plants. Light and epi-fluorescence microscopy analyses showed that leaves of inoculated plants had higher density of smaller stomata (297 vs. 247 n/mm2), thicker palisade parenchyma (95.0 vs. 85.8 μm), and larger intercellular spaces in the mesophyll (57.5% vs. 52.2%), compared to non-inoculated plants. The modifications in leaf functional anatomical traits affected gas exchanges; in fact starting from the reproductive phase, the rate of leaf net photosynthesis (NP) was higher in inoculated compared to control plants (8.69 vs. 6.13 μmol CO2 m-2 s-1 at the beginning of flowering). These data are consistent with the better maximal PSII photochemical efficiency observed in inoculated plants (0.807 vs. 0.784 in control); conversely no difference in leaf chlorophyll content was found. The PGPM-induced changes in leaf structure and photosynthesis lead to an improvement of plant growth (+29.9% in plant leaf area) and seed yield (+36.9%) compared to control. Our results confirm that PGPMs may confer benefits in photosynthetic traits of soybean plants even in hydroponics (i.e., NFT), with positive effects on growth and seed production, prefiguring potential application of beneficial microorganisms in plant cultivation in hydroponics.

Toward biotechnology in space: High-throughput instruments for in situ biological research beyond Earth

Space biotechnology is a nascent field aimed at applying tools of modern biology to advance our goals in space exploration. These advances rely on our ability to exploit in situ high throughput techniques for amplification and sequencing DNA, and measuring levels of RNA transcripts, proteins and metabolites in a cell. These techniques, collectively known as "omics" techniques have already revolutionized terrestrial biology. A number of on-going efforts are aimed at developing instruments to carry out "omics" research in space, in particular on board the International Space Station and small satellites. For space applications these instruments require substantial and creative reengineering that includes automation, miniaturization and ensuring that the device is resistant to conditions in space and works independently of the direction of the gravity vector. Different paths taken to meet these requirements for different "omics" instruments are the subjects of this review. The advantages and disadvantages of these instruments and technological solutions and their level of readiness for deployment in space are discussed. Considering that effects of space environments on terrestrial organisms appear to be global, it is argued that high throughput instruments are essential to advance (1) biomedical and physiological studies to control and reduce space-related stressors on living systems, (2) application of biology to life support and in situ resource utilization, (3) planetary protection, and (4) basic research about the limits on life in space. It is also argued that carrying out measurements in situ provides considerable advantages over the traditional space biology paradigm that relies on post-flight data analysis.

Microbial Community Dynamics and Response to Plant Growth-Promoting Microorganisms in the Rhizosphere of Four Common Food Crops Cultivated in Hydroponics

Plant growth promoting microorganisms (PGPMs) of the plant root zone microbiome have received limited attention in hydroponic cultivation systems. In the framework of a project aimed at the development of a biological life support system for manned missions in space, we investigated the effects of PGPMs on four common food crops (durum and bread wheat, potato and soybean) cultivated in recirculating hydroponic systems for a whole life cycle. Each crop was inoculated with a commercial PGPM mixture and the composition of the microbial communities associated with their root rhizosphere, rhizoplane/endosphere and with the recirculating nutrient solution was characterised through 16S- and ITS-targeted Illumina MiSeq sequencing. PGPM addition was shown to induce changes in the composition of these communities, though these changes varied both between crops and over time. Microbial communities of PGPM-treated plants were shown to be more stable over time. Though additional development is required, this study highlights the potential benefits that PGPMs may confer to plants grown in hydroponic systems, particularly when cultivated in extreme environments such as space.

Microgravity-driven remodeling of the proteome reveals insights into molecular mechanisms and signal networks involved in response to the space flight environment

Space is a hostile environment characterized by high vacuum, extreme temperatures, meteoroids, space debris, ionospheric plasma, microgravity and space radiation, which all represent risks for human health. A deep understanding of the biological consequences of exposure to the space environment is required to design efficient countermeasures to minimize their negative impact on human health. Recently, proteomic approaches have received a significant amount of attention in the effort to further study microgravity-induced physiological changes. In this review, we summarize the current knowledge about the effects of microgravity on microorganisms (in particular Cupriavidus metallidurans CH34, Bacillus cereus and Rhodospirillum rubrum S1H), plants (whole plants, organs, and cell cultures), mammalian cells (endothelial cells, bone cells, chondrocytes, muscle cells, thyroid cancer cells, immune system cells) and animals (invertebrates, vertebrates and mammals). Herein, we describe their proteome's response to microgravity, focusing on proteomic discoveries and their future potential applications in space research.

BIOLOGICAL SIGNIFICANCE

Space experiments and operational flight experience have identified detrimental effects on human health and performance because of exposure to weightlessness, even when currently available countermeasures are implemented. Many experimental tools and methods have been developed to study microgravity induced physiological changes. Recently, genomic and proteomic approaches have received a significant amount of attention. This review summarizes the recent research studies of the proteome response to microgravity inmicroorganisms, plants, mammalians cells and animals. Current proteomic tools allow large-scale, high-throughput analyses for the detection, identification, and functional investigation of all proteomes. Understanding gene and/or protein expression is the key to unlocking the mechanisms behind microgravity-induced problems and to finding effective countermeasures to spaceflight-induced alterations but also for the study of diseases on earth. Future perspectives are also highlighted.

Effect of bacterial root symbiosis and urea as source of nitrogen on performance of soybean plants grown hydroponically for Bioregenerative Life Support Systems (BLSSs)

Soybean is traditionally grown in soil, where root symbiosis with Bradyrhizobium japonicum can supply nitrogen (N), by means of bacterial fixation of atmospheric N2. Nitrogen fertilizers inhibit N-fixing bacteria. However, urea is profitably used in soybean cultivation in soil, where urease enzymes of telluric microbes catalyze the hydrolysis to ammonium, which has a lighter inhibitory effect compared to nitrate. Previous researches demonstrated that soybean can be grown hydroponically with recirculating complete nitrate-based nutrient solutions. In Space, urea derived from crew urine could be used as N source, with positive effects in resource procurement and waste recycling. However, whether the plants are able to use urea as the sole source of N and its effect on root symbiosis with B. japonicum is still unclear in hydroponics. We compared the effect of two N sources, nitrate and urea, on plant growth and physiology, and seed yield and quality of soybean grown in closed-loop Nutrient Film Technique (NFT) in growth chamber, with or without inoculation with B. japonicum. Urea limited plant growth and seed yield compared to nitrate by determining nutrient deficiency, due to its low utilization efficiency in the early developmental stages, and reduced nutrients uptake (K, Ca, and Mg) throughout the whole growing cycle. Root inoculation with B. japonicum did not improve plant performance, regardless of the N source. Specifically, nodulation increased under fertigation with urea compared to nitrate, but this effect did not result in higher leaf N content and better biomass and seed production. Urea was not suitable as sole N source for soybean in closed-loop NFT. However, the ability to use urea increased from young to adult plants, suggesting the possibility to apply it during reproductive phase or in combination with nitrate in earlier developmental stages. Root symbiosis did not contribute significantly to N nutrition and did not enhance the plant ability to use urea, possibly because of ineffective infection process and nodule functioning in hydroponics.

Transcriptional response of Arabidopsis seedlings during spaceflight reveals peroxidase and cell wall remodeling genes associated with root hair development

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PREMISE OF THE STUDY

Plants will be an important component of advanced life support systems during space exploration missions. Therefore, understanding their biology in the spacecraft environment will be essential before they can be used for such systems.•

METHODS

Seedlings of Arabidopsis thaliana were grown for 2 wk in the Biological Research in Canisters (BRIC) hardware on board the second to the last mission of the space shuttle Discovery (STS-131). Transcript profiles between ground controls and space-grown seedlings were compared using stringent selection criteria.•

KEY RESULTS

Expression of transcripts associated with oxidative stress and cell wall remodeling was repressed in microgravity. These downregulated genes were previously shown to be enriched in root hairs consistent with seedling phenotypes observed in space. Mutations in genes that were downregulated in microgravity, including two uncharacterized root hair-expressed class III peroxidase genes (PRX44 and PRX57), led to defective polar root hair growth on Earth. PRX44 and PRX57 mutants had ruptured root hairs, which is a typical phenotype of tip-growing cells with defective cell walls and those subjected to stress.•

CONCLUSIONS

Long-term exposure to microgravity negatively impacts tip growth by repressing expression of genes essential for normal root hair development. Whereas changes in peroxidase gene expression leading to reduced root hair growth in space are actin-independent, root hair development modulated by phosphoinositides could be dependent on the actin cytoskeleton. These results have profound implications for plant adaptation to microgravity given the importance of tip growing cells such as root hairs for efficient nutrient capture.

Photosynthesis at the forefront of a sustainable life

The development of a sustainable bio-based economy has drawn much attention in recent years, and research to find smart solutions to the many inherent challenges has intensified. In nature, perhaps the best example of an authentic sustainable system is oxygenic photosynthesis. The biochemistry of this intricate process is empowered by solar radiation influx and performed by hierarchically organized complexes composed by photoreceptors, inorganic catalysts, and enzymes which define specific niches for optimizing light-to-energy conversion. The success of this process relies on its capability to exploit the almost inexhaustible reservoirs of sunlight, water, and carbon dioxide to transform photonic energy into chemical energy such as stored in adenosine triphosphate. Oxygenic photosynthesis is responsible for most of the oxygen, fossil fuels, and biomass on our planet. So, even after a few billion years of evolution, this process unceasingly supports life on earth, and probably soon also in outer-space, and inspires the development of enabling technologies for a sustainable global economy and ecosystem. The following review covers some of the major milestones reached in photosynthesis research, each reflecting lasting routes of innovation in agriculture, environmental protection, and clean energy production.

Effects of the Extraterrestrial Environment on Plants: Recommendations for Future Space Experiments for the MELiSSA Higher Plant Compartment

Due to logistical challenges, long-term human space exploration missions require a life support system capable of regenerating all the essentials for survival. Higher plants can be utilized to provide a continuous supply of fresh food, atmosphere revitalization, and clean water for humans. Plants can adapt to extreme environments on Earth, and model plants have been shown to grow and develop through a full life cycle in microgravity. However, more knowledge about the long term effects of the extraterrestrial environment on plant growth and development is necessary. The European Space Agency (ESA) has developed the Micro-Ecological Life Support System Alternative (MELiSSA) program to develop a closed regenerative life support system, based on micro-organisms and higher plant processes, with continuous recycling of resources. In this context, a literature review to analyze the impact of the space environments on higher plants, with focus on gravity levels, magnetic fields and radiation, has been performed. This communication presents a roadmap giving directions for future scientific activities within space plant cultivation. The roadmap aims to identify the research activities required before higher plants can be included in regenerative life support systems in space.

Leaf anatomy and photochemical behaviour of Solanum lycopersicum L. plants from seeds irradiated with low-LET ionising radiation

Plants can be exposed to ionising radiation not only in Space but also on Earth, due to specific technological applications or after nuclear disasters. The response of plants to ionising radiation depends on radiation quality/quantity and/or plant characteristics. In this paper, we analyse some growth traits, leaf anatomy, and ecophysiological features of plants of Solanum lycopersicum L. "Microtom" grown from seeds irradiated with increasing doses of X-rays (0.3, 10, 20, 50, and 100 Gy). Both juvenile and compound leaves from plants developed from irradiated and control seeds were analysed through light and epifluorescence microscopy. Digital image analysis allowed quantifying anatomical parameters to detect the occurrence of signs of structural damage. Fluorescence parameters and total photosynthetic pigment content were analysed to evaluate the functioning of the photosynthetic machinery. Radiation did not affect percentage and rate of seed germination. Plants from irradiated seeds accomplished the crop cycle and showed a more compact habitus. Dose-depended tendencies of variations occurred in phenolic content, while other leaf anatomical parameters did not show distinct trends after irradiation. The sporadic perturbations of leaf structure, observed during the vegetative phase, after high levels of radiation were not so severe as to induce any significant alterations in photosynthetic efficiency.

Microgravity effects on different stages of higher plant life cycle and completion of the seed-to-seed cycle

Human inhabitation of Space requires the efficient realisation of crop cultivation in bioregenerative life-support systems (BLSS). It is well known that plants can grow under Space conditions; however, perturbations of many biological phenomena have been highlighted due to the effect of altered gravity and its possible interactions with other factors. The mechanisms priming plant responses to Space factors, as well as the consequences of such alterations on crop productivity, have not been completely elucidated. These perturbations can occur at different stages of plant life and are potentially responsible for failure of the completion of the seed-to-seed cycle. After brief consideration of the main constraints found in the most recent experiments aiming to produce seeds in Space, we focus on two developmental phases in which the plant life cycle can be interrupted more easily than in others also on Earth. The first regards seedling development and establishment; we discuss reasons for slow development at the seedling stage that often occurs under microgravity conditions and can reduce successful establishment. The second stage comprises gametogenesis and pollination; we focus on male gamete formation, also identifying potential constraints to subsequent fertilisation. We finally highlight how similar alterations at cytological level can not only be common to different processes occurring at different life stages, but can be primed by different stress factors; such alterations can be interpreted within the model of 'stress-induced morphogenic response' (SIMR). We conclude by suggesting that a systematic analysis of all growth and reproductive phases during the plant life cycle is needed to optimise resource use in plant-based BLSS.

Plant biology in space: recent accomplishments and recommendations for future research

Gravity has shaped the evolution of life since its origin. However, experiments in the absence of this overriding force, necessary to precisely analyse its role, e.g. for growth, development, and orientation of plants and single cells, only became possible with the advent of spaceflight. Consequently, this research has been supported especially by space agencies around the world for decades, mainly for two reasons: first, to enable fundamental research on gravity perception and transduction during growth and development of plants; and second, to successfully grow plants under microgravity conditions with the goal of establishing a bioregenerative life support system providing oxygen and food for astronauts in long-term exploratory missions. For the second time, the International Space Life Sciences Working Group (ISLSWG), comprised of space agencies with substantial life sciences programmes in the world, organised a workshop on plant biology research in space. The present contribution summarises the outcome of this workshop. In the first part, an analysis is undertaken, if and how the recommendations of the first workshop held in Bad Honnef, Germany, in 1996 have been implemented. A chapter summarising major scientific breakthroughs obtained in the last 15 years from plant research in space concludes this first part. In the second part, recommendations for future research in plant biology in space are put together that have been elaborated in the various discussion sessions during the workshop, as well as provided in written statements from the session chairs. The present paper clearly shows that plant biology in space has contributed significantly to progress in plant gravity perception, transduction and responses - processes also relevant for general plant biology, including agricultural aspects. In addition, the interplay between light and gravity effects has increasingly received attention. It also became evident that plants will play a major role as components of bioregenerative life support and energy systems that are necessary to complement physico-chemical systems in upcoming long-term exploratory missions. In order to achieve major progress in the future, however, standardised experimental conditions and more advanced analytical tools, such as state-of-the-art onboard analysis, are required.