Biologically-Based and Physiochemical Life Support and In Situ Resource Utilization for Exploration of the Solar System-Reviewing the Current State and Defining Future Development Needs

Alga-based mathematical model of a life support system closed in oxygen and carbon dioxide

The purpose of the study was to compare quantitative analysis methods used in the early stages of closed-loop system prototyping with modern data analysis approaches. As an example, a mathematical model of the stable coexistence of two microalgae in a mixed flow culture, proposed by Bolsunovsky and Degermendzhi in 1982, is considered. The model is built on the basis of a detailed theoretical description of the interaction between species and substrate (in this case, illumination). The ability to control the species ratio allows you to adjust the assimilation quotient (AQ), that is, the ratio of carbon dioxide absorbed to oxygen released. The problem of controlling the assimilation coefficient of a life support system is still relevant; in modern works, microalgae are considered as promising oxygen generators. At the same time, modern works place emphasis on empirical modeling methods, in particular, on the analysis of big data, and the work does not go beyond the task of managing a monoculture of microalgae. In our work, we pay attention to three results that, in our opinion, successfully complement modern methods. Firstly, the model allows the use of results from experiments with monocultures. Secondly, the model predicts the transformation of data into a form convenient for further analysis, including for calculating AQ. Thirdly, the model allows us to guarantee the stability of the resulting approximation and further refine the solution by small corrections using empirical methods.

Toward sustainable space exploration: a roadmap for harnessing the power of microorganisms

Finding sustainable approaches to achieve independence from terrestrial resources is of pivotal importance for the future of space exploration. This is relevant not only to establish viable space exploration beyond low Earth-orbit, but also for ethical considerations associated with the generation of space waste and the preservation of extra-terrestrial environments. Here we propose and highlight a series of microbial biotechnologies uniquely suited to establish sustainable processes for in situ resource utilization and loop-closure. Microbial biotechnologies research and development for space sustainability will be translatable to Earth applications, tackling terrestrial environmental issues, thereby supporting the United Nations Sustainable Development Goals.

Cyanobacteria and Algal-Based Biological Life Support System (BLSS) and Planetary Surface Atmospheric Revitalizing Bioreactor Brief Concept Review

Exploring austere environments required a reimagining of resource acquisition and utilization. Cyanobacterial in situ resources utilization (ISRU) and biological life support system (BLSS) bioreactors have been proposed to allow crewed space missions to extend beyond the temporal boundaries that current vehicle mass capacities allow. Many cyanobacteria and other microscopic organisms evolved during a period of Earth’s history that was marked by very harsh conditions, requiring robust biochemical systems to ensure survival. Some species work wonderfully in a bioweathering capacity (siderophilic), and others are widely used for their nutritional power (non-siderophilic). Playing to each of their strengths and having them grow and feed off of each other is the basis for the proposed idea for a series of three bioreactors, starting from regolith processing and proceeding to nutritional products, gaseous liberation, and biofuel production. In this paper, we discuss what that three reactor system will look like, with the main emphasis on the nutritional stage.

Glycogen metabolism is required for optimal cyanobacterial growth in the rapid light-dark cycle of low-Earth orbit

Some designs for bioregenerative life support systems to enable human space missions incorporate cyanobacteria for removal of carbon dioxide, generation of oxygen, and treatment of wastewater, as well as providing a source of nutrition. In this study, we examined the effects of the short light-dark (LD) cycle of low-Earth orbit on algal and cyanobacterial growth, approximating conditions on the International Space Station, which orbits Earth roughly every 90 min. We found that growth of green algae was similar in both normal 12 h light:12 h dark (12 h:12 h LD) and 45':45' LD cycles. Three diverse strains of cyanobacteria were not only capable of growth in short 45':45' LD cycles, but actually grew better than in 12 h:12 h LD cycles. We showed that 45':45' LD cycles do not affect the endogenous 24 h circadian rhythms of Synechococcus elongatus. Using a dense library of randomly barcoded transposon mutants, we identified genes whose loss is detrimental for the growth of S. elongatus under 45':45' LD cycles. These include several genes involved in glycogen metabolism and the oxidative pentose phosphate pathway. Notably, 45':45' LD cycles did not affect the fitness of strains that carry mutations in the biological circadian oscillator or the clock input and output regulatory pathways. Overall, this study shows that cultures of cyanobacteria could be grown under natural sunlight of low-Earth orbit and highlights the utility of a functional genomic study in a model organism to better understand key biological processes in conditions that are relevant to space travel.

The chemical neighborhood of cells in a diffusion-limited system

Microorganisms follow us everywhere, and they will be essential to sustaining long-term human space exploration through applications such as vitamin synthesis, biomining, and more. Establishing a sustainable presence in space therefore requires that we better understand how stress due to the altered physical conditions of spaceflight affects our companion organisms. In microgravity environments such as orbital space stations, microorganisms likely experience the change in gravity primarily through changes in fluid mixing processes. Without sedimentation and density-driven convection, diffusion becomes the primary process governing the movement of growth substrates and wastes for microbial cells in suspension culture. Non-motile cells might therefore develop a substrate-deficient "zone of depletion" and experience stress due to starvation and/or waste build-up. This would in turn impact the concentration-dependent uptake rate of growth substrates and could be the cause of the altered growth rates previously observed in microorganisms in spaceflight and in ground-simulated microgravity. To better understand the extent of these concentration differences and their potential influence on substrate uptake rates, we used both an analytical solution and finite difference method to visualize concentration fields around individual cells. We modeled diffusion, using Fick's Second Law, and nutrient uptake, using Michaelis-Menten kinetics, and assessed how that distribution varies in systems with multiple cells and varied geometries. We determined the radius of the zone of depletion, within which cells had reduced the substrate concentration by 10%, to be 5.04 mm for an individual Escherichia coli cell in the conditions we simulated. However, we saw a synergistic effect with multiple cells near each other: multiple cells in close proximity decreased the surrounding concentration by almost 95% from the initial substrate concentration. Our calculations provide researchers an inside look at suspension culture behavior in the diffusion-limited environment of microgravity at the scale of individual cells.

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.