Suitability of different photosynthetic organisms for an extraterrestrial biological life support system

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.

Lipid Rafts and Plant Gravisensitivity

The necessity to include plants as a component of a Bioregenerative Life Support System leads to investigations to optimize plant growth facilities as well as a better understanding of the plant cell membrane and its numerous activities in the signaling, transport, and sensing of gravity, drought, and other stressors. The cell membrane participates in numerous processes, including endo- and exocytosis and cell division, and is involved in the response to external stimuli. Variable but stabilized microdomains form in membranes that include specific lipids and proteins that became known as (detergent-resistant) membrane microdomains, or lipid rafts with various subclassifications. The composition, especially the sterol-dependent recruitment of specific proteins affects endo- and exo-membrane domains as well as plasmodesmata. The enhanced saturated fatty acid content in lipid rafts after clinorotation suggests increased rigidity and reduced membrane permeability as a primary response to abiotic and mechanical stress. These results can also be obtained with lipid-sensitive stains. The linkage of the CM to the cytoskeleton via rafts is part of the complex interactions between lipid microdomains, mechanosensitive ion channels, and the organization of the cytoskeleton. These intricately linked structures and functions provide multiple future research directions to elucidate the role of lipid rafts in physiological processes.

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.

A Low-Pressure, N2/CO2 Atmosphere Is Suitable for Cyanobacterium-Based Life-Support Systems on Mars

The leading space agencies aim for crewed missions to Mars in the coming decades. Among the associated challenges is the need to provide astronauts with life-support consumables and, for a Mars exploration program to be sustainable, most of those consumables should be generated on site. Research is being done to achieve this using cyanobacteria: fed from Mars's regolith and atmosphere, they would serve as a basis for biological life-support systems that rely on local materials. Efficiency will largely depend on cyanobacteria's behavior under artificial atmospheres: a compromise is needed between conditions that would be desirable from a purely engineering and logistical standpoint (by being close to conditions found on the Martian surface) and conditions that optimize cyanobacterial productivity. To help identify this compromise, we developed a low-pressure photobioreactor, dubbed Atmos, that can provide tightly regulated atmospheric conditions to nine cultivation chambers. We used it to study the effects of a 96% N2, 4% CO2 gas mixture at a total pressure of 100 hPa on Anabaena sp. PCC 7938. We showed that those atmospheric conditions (referred to as MDA-1) can support the vigorous autotrophic, diazotrophic growth of cyanobacteria. We found that MDA-1 did not prevent Anabaena sp. from using an analog of Martian regolith (MGS-1) as a nutrient source. Finally, we demonstrated that cyanobacterial biomass grown under MDA-1 could be used for feeding secondary consumers (here, the heterotrophic bacterium E. coli W). Taken as a whole, our results suggest that a mixture of gases extracted from the Martian atmosphere, brought to approximately one tenth of Earth's pressure at sea level, would be suitable for photobioreactor modules of cyanobacterium-based life-support systems. This finding could greatly enhance the viability of such systems on Mars.

Extremophile Microalgae: the potential for biotechnological application

Microalgae are photosynthetic microorganisms that use sunlight as an energy source, and convert water, carbon dioxide, and inorganic salts into algal biomass. The isolation and selection of microalgae, which allow one to obtain large amounts of biomass and valuable compounds, is a prerequisite for their successful industrial production. This work provides an overview of extremophile algae, where their ability to grow under harsh conditions and the corresponding accumulation of metabolites are addressed. Emphasis is placed on the high-value products of some prominent algae. Moreover, the most recent applications of these microorganisms and their potential exploitation in the context of astrobiology are taken into account.

High density long-term cultivation of Chlorella vulgaris SAG 211-12 in a novel microgravity-capable membrane raceway photobioreactor for future bioregenerative life support in SPACE

Hybrid life support systems are of great interest for future far-distant space exploration missions to planetary surfaces, e.g. Mars, planned until 2050. By synergistically combining physicochemical and biotechnological algae-based subsystems, an essential step towards the closure of the carbon loop in environmental control and life support systems (ECLSS) shall be accomplished, offering a wide beneficial potential for ECLSS through the utilization of oxygenic photosynthesis: O₂ and potential human food can be formed in-situ from CO₂ and water. The wild type green alga Chlorella vulgaris strain SAG 211-12 was selected as model microorganism due to its photoautotrophic growth, high biomass yield, cultivation flexibility and long-term cultivation robustness. The current study presents for the first time a stable xenic long-term processing of microalgae in a novel microgravity capable membrane raceway photobioreactor for 188 days with the focus on algal growth kinetics and gas evolution. In particular, culture homogeneity and viability were monitored and evaluated during the whole cultivation process due to their putative crucial impact on long-term functionality and efficiency of a closed cultivation system. Based on a specially designed cyclic batch cultivation process for SAG 211-12, a successive biomass growth up to a maximum of 12.2 g l^-1 with a max. global volumetric productivity of 1.3 g l^-1 d^-1 was reached within the closed loop system. The photosynthetic capacity was assessed to a global molar photosynthetic quotient of 0.31. Furthermore, cultivation parameters for a change from batch to continuous processing at high biomass densities and proliferation rates are introduced. The presented µgPBR miniature plant and the developed high throughput cultivation process are planned to be tested under real space conditions within the PBR@LSR project (microgravity and cosmic radiation) aboard the International Space Station with an operation period of up to 180 days to investigate the impact on long-term system stability.

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.

Elevated CO2 enhances photosynthetic efficiency, ion uptake and antioxidant activity of Gynura bicolor DC. grown in a porous-tube nutrient delivery system under simulated microgravity

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 interaction with other factors (e.g., CO2 , ion radiation, etc. Our aim was to test whether elevated CO2 could provide 'protection' to Gynura bicolor against the damaging effects of simulated microgravity (SM) on photosynthesis, ion uptake and antioxidant activity. As compared to G. bicolor grown in ambient CO2 with no SM (ACO2 ), growth and yield of the plants increased under elevated ambient CO2 with no SM (ECO2 ) and decreased under ACO2 +SM, whereas there was no significant effect on ECO2 +SM. Reductions in the content of Chl a, carotenoids and Chl a+b were 17.9%, 20.7% and 17.9% under ACO2 +SM, respectively, but under ECO2 there was a significant effect on all photosynthetic pigments except Chl b, compared to ACO2 . Photosynthesis was improved under ECO2 with SM and such an improvement was associated with improved water use efficiency and instantaneous carboxylation efficiency. Furthermore, SM caused a reduction in ion absorption rate, except for Ca(2+) , while ECO2 increased the uptake rate. Finally, the activity of SOD, POD and the content of MDA and H2 O2 were enhanced under SM treatments and were highest in ACO2 +SM. In contrast, T-AOC activity and GSH content significantly declined in ACO2 +SM compared to other treatments. These results suggest that ACO2 is not sufficient to counteract SM impact, but the increase is usually caused by improvement in CO2 nutrition in ECO2 +SM in comparison with ACO2 +SM.

Pressurized Martian-Like Pure CO2 Atmosphere Supports Strong Growth of Cyanobacteria, and Causes Significant Changes in their Metabolism

Surviving of crews during future missions to Mars will depend on reliable and adequate supplies of essential life support materials, i.e. oxygen, food, clean water, and fuel. The most economical and sustainable (and in long term, the only viable) way to provide these supplies on Martian bases is via bio-regenerative systems, by using local resources to drive oxygenic photosynthesis. Selected cyanobacteria, grown in adequately protective containment could serve as pioneer species to produce life sustaining substrates for higher organisms. The very high (95.3 %) CO₂ content in Martian atmosphere would provide an abundant carbon source for photo-assimilation, but nitrogen would be a strongly limiting substrate for bio-assimilation in this environment, and would need to be supplemented by nitrogen fertilizing. The very high supply of carbon, with rate-limiting supply of nitrogen strongly affects the growth and the metabolic pathways of the photosynthetic organisms. Here we show that modified, Martian-like atmospheric composition (nearly 100 % CO₂) under various low pressure conditions (starting from 50 mbar to maintain liquid water, up to 200 mbars) supports strong cellular growth. Under high CO₂ / low N₂ ratio the filamentous cyanobacteria produce significant amount of H₂ during light due to differentiation of high amount of heterocysts.

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.

Mutations of photosystem II D1 protein that empower efficient phenotypes of Chlamydomonas reinhardtii under extreme environment in space

Space missions have enabled testing how microorganisms, animals and plants respond to extra-terrestrial, complex and hazardous environment in space. Photosynthetic organisms are thought to be relatively more prone to microgravity, weak magnetic field and cosmic radiation because oxygenic photosynthesis is intimately associated with capture and conversion of light energy into chemical energy, a process that has adapted to relatively less complex and contained environment on Earth. To study the direct effect of the space environment on the fundamental process of photosynthesis, we sent into low Earth orbit space engineered and mutated strains of the unicellular green alga, Chlamydomonas reinhardtii, which has been widely used as a model of photosynthetic organisms. The algal mutants contained specific amino acid substitutions in the functionally important regions of the pivotal Photosystem II (PSII) reaction centre D1 protein near the Q_B binding pocket and in the environment surrounding Tyr-161 (Y_Z) electron acceptor of the oxygen-evolving complex. Using real-time measurements of PSII photochemistry, here we show that during the space flight while the control strain and two D1 mutants (A250L and V160A) were inefficient in carrying out PSII activity, two other D1 mutants, I163N and A251C, performed efficient photosynthesis, and actively re-grew upon return to Earth. Mimicking the neutron irradiation component of cosmic rays on Earth yielded similar results. Experiments with I163N and A251C D1 mutants performed on ground showed that they are better able to modulate PSII excitation pressure and have higher capacity to reoxidize the Q_A⁻ state of the primary electron acceptor. These results highlight the contribution of D1 conformation in relation to photosynthesis and oxygen production in space.

Screening and genetic manipulation of green organisms for establishment of biological life support systems in space

Curiosity has driven humankind to explore and conquer space. However, today, space research is not a means to relieve this curiosity anymore, but instead has turned into a need. To support the crew in distant expeditions, supplies should either be delivered from the Earth, or prepared for short durations through physiochemical methods aboard the space station. Thus, research continues to devise reliable regenerative systems. Biological life support systems may be the only answer to human autonomy in outposts beyond Earth. For construction of an artificial extraterrestrial ecosystem, it is necessary to search for highly adaptable super-organisms capable of growth in harsh space environments. Indeed, a number of organisms have been proposed for cultivation in space. Meanwhile, some manipulations can be done to increase their photosynthetic potential and stress tolerance. Genetic manipulation and screening of plants, microalgae and cyanobacteria is currently a fascinating topic in space bioengineering. In this commentary, we will provide a viewpoint on the realities, limitations and promises in designing biological life support system based on engineered and/or selected green organism. Special focus will be devoted to the engineering of key photosynthetic enzymes in pioneer green organisms and their potential use in establishment of transgenic photobioreactors in space.

Survival of akinetes (resting-state cells of cyanobacteria) in low earth orbit and simulated extraterrestrial conditions

Cyanobacteria are photosynthetic organisms that have been considered for space applications, such as oxygen production in bioregenerative life support systems, and can be used as a model organism for understanding microbial survival in space. Akinetes are resting-state cells of cyanobacteria that are produced by certain genera of heterocystous cyanobacteria to survive extreme environmental conditions. Although they are similar in nature to endospores, there have been no investigations into the survival of akinetes in extraterrestrial environments. The aim of this work was to examine the survival of akinetes from Anabaena cylindrica in simulated extraterrestrial conditions and in Low Earth Orbit (LEO). Akinetes were dried onto limestone rocks and sent into LEO for 10 days on the ESA Biopan VI. In ground-based experiments, the rocks were exposed to periods of desiccation, vacuum (0.7×10(-3) kPa), temperature extremes (-80 to 80°C), Mars conditions (-27°C, 0.8 kPa, CO(2)) and UV radiation (325-400 nm). A proportion of the akinete population was able to survive a period of 10 days in LEO and 28 days in Mars simulated conditions, when the rocks were not subjected to UV radiation. Furthermore, the akinetes were able to survive 28 days of exposure to desiccation and low temperature with high viability remaining. Yet long periods of vacuum and high temperature were lethal to the akinetes. This work shows that akinetes are extreme-tolerating states of cyanobacteria that have a practical use in space applications and yield new insight into the survival of microbial resting-state cells in space conditions.

Geomicrobiology beyond Earth: microbe-mineral interactions in space exploration and settlement

Geomicrobiology investigates the interactions of microorganisms with geological substrates, and this branch of microbiology has enormous potential in the exploration and settlement of space. Microorganisms can be used to extract useful elements from extraterrestrial materials for industrial processes or for use as nutrients in life support systems. In addition, microorganisms could be used to create soil from lunar and Martian rocks. Furthermore, understanding the interactions of microorganisms with rocks is essential for identifying mineral biomarkers to be used in the search for life on other planetary bodies. Increasing space exploration activities make geomicrobiology an important applied science beyond Earth.

From the deep sea to the stars: human life support through minimal communities

Support of human life during long-distance exploratory space travel or in the creation of human habitats in extreme environments can be accomplished using the action of microbial consortia inhabiting interconnected bioreactors, designed for the purpose of reconversion of solid, liquid and gaseous wastes produced by the human crew or by one of the compartments of the bioregenerative loop, into nutritional biomass, oxygen and potable water. The microorganisms responsible for bioregenerative life support are part of Earth's own geomicrobial reconversion cycle. Depending on the resources and conditions available, minimal life support systems can be assembled using appropriately selected microorganisms that possess metabolic routes for each specific purpose in the transformation cycle. Under control of an engineered system, a reliable life-support system can hence be provided for.