Reactivation of Microbial Strains and Synthetic Communities After a Spaceflight to the International Space Station: Corroborating the Feasibility of Essential Conversions in the MELiSSA Loop

Recovery of purple non-sulfur bacteria-mediated single-cell protein from domestic wastewater in two-stage treatment using high rate digester and raceway pond

Wastewater resources can be used to produce microbial protein for animal feed or organic fertiliser, conserving food chain resources. This investigation hasemployed thefermented sewage to photoheterotrophically grown purple non-sulfur bacteria (PNSB) in a 2.5 m3 pilot-scaleraceway-pond with infrared light to produce proteinaceous biomass. Fermented sewage with synthetic media consisting of sodium acetate and propionic acids at a surface-to-volume (S/V) ratio of 10 m2/m3 removed 89%, 93%, and 81% of chemical oxygen demand, ammonium nitrogen, and orthophosphate, respectively; whereas respective removal in fermented sewage alone without synthetic media was 73%, 73%, and 72% during batch operation of 120 h. The biomass yield of 0.88-0.95 g CODbiomass /g CODremoved with protein content of 40.3 ± 0.3%-43.9 ± 0.2% w/w was obtained for fermented sewage with synthetic media. The results revealed enhanced possibility of scaling-up the raceway reactor to recover resources from municipal wastewater and enable simultaneous high-rate PNSB single-cell protein production.

Microbiology of human spaceflight: microbial responses to mechanical forces that impact health and habitat sustainability

SUMMARYUnderstanding the dynamic adaptive plasticity of microorganisms has been advanced by studying their responses to extreme environments. Spaceflight research platforms provide a unique opportunity to study microbial characteristics in new extreme adaptational modes, including sustained exposure to reduced forces of gravity and associated low fluid shear force conditions. Under these conditions, unexpected microbial responses occur, including alterations in virulence, antibiotic and stress resistance, biofilm formation, metabolism, motility, and gene expression, which are not observed using conventional experimental approaches. Here, we review biological and physical mechanisms that regulate microbial responses to spaceflight and spaceflight analog environments from both the microbe and host-microbe perspective that are relevant to human health and habitat sustainability. We highlight instrumentation and technology used in spaceflight microbiology experiments, their limitations, and advances necessary to enable next-generation research. As spaceflight experiments are relatively rare, we discuss ground-based analogs that mimic aspects of microbial responses to reduced gravity in spaceflight, including those that reduce mechanical forces of fluid flow over cell surfaces which also simulate conditions encountered by microorganisms during their terrestrial lifecycles. As spaceflight mission durations increase with traditional astronauts and commercial space programs send civilian crews with underlying health conditions, microorganisms will continue to play increasingly critical roles in health and habitat sustainability, thus defining a new dimension of occupational health. The ability of microorganisms to adapt, survive, and evolve in the spaceflight environment is important for future human space endeavors and provides opportunities for innovative biological and technological advances to benefit life on Earth.

Radiotolerance of N-cycle bacteria and their transcriptomic response to low-dose space-analogue ionizing irradiation

The advancement of regenerative life support systems (RLSS) is crucial to allow long-distance space travel. Within the Micro-Ecological Life Support System Alternative (MELiSSA), efficient nitrogen recovery from urine and other waste streams is vital to produce liquid fertilizer to feed food and oxygen production in subsequent photoautotrophic processes. This study explores the effects of ionizing radiation on nitrogen cycle bacteria that transform urea to nitrate. In particular, we assess the radiotolerance of Comamonas testosteroni, Nitrosomonas europaea, and Nitrobacter winogradskyi after exposure to acute γ-irradiation. Moreover, a comprehensive whole transcriptome analysis elucidates the effects of spaceflight-analogue low-dose ionizing radiation on the individual axenic strains and on their synthetic community o. This research sheds light on how the spaceflight environment could affect ureolysis and nitrification processes from a transcriptomic perspective.

Recycling nutrients from organic waste for growing higher plants in the Micro Ecological Life Support System Alternative (MELiSSA) loop during long-term space missions

Space agencies are developing Bioregenerative Life Support Systems (BLSS) in view of upcoming long-term crewed space missions. Most of these BLSS plan to include various crops to produce different types of foods, clean water, and O2 while capturing CO2 from the atmosphere. However, growing these plants will require the appropriate addition of nutrients in forms that are available. As shipping fertilizers from Earth would be too costly, it will be necessary to use waste-derived nutrients. Using the example of the MELiSSA (Micro-Ecological Life Support System Alternative) loop of the European Space Agency, this paper reviews what should be considered so that nutrients recycled from waste streams could be used by plants grown in a hydroponic system. Whereas substantial research has been conducted on nitrogen and phosphorus recovery from human urine, much work remains to be done on recovering nutrients from other liquid and solid organic waste. It is essential to continue to study ways to efficiently remove sodium and chloride from urine and other organic waste to prevent the spread of these elements to the rest of the MELiSSA loop. A full nitrogen balance at habitat level will have to be achieved; on one hand, sufficient N2 will be needed to maintain atmospheric pressure at a proper level and on the other, enough mineral nitrogen will have to be provided to the plants to ensure biomass production. From a plant nutrition point of view, we will need to evaluate whether the flux of nutrients reaching the hydroponic system will enable the production of nutrient solutions able to sustain a wide variety of crops. We will also have to assess the nutrient use efficiency of these crops and how that efficiency might be increased. Techniques and sensors will have to be developed to grow the plants, considering low levels or the total absence of gravity, the limited volume available to plant growth systems, variations in plant needs, the recycling of nutrient solutions, and eventually the ultimate disposal of waste that can no longer be used.

Whole transcriptome analysis highlights nutrient limitation of nitrogen cycle bacteria in simulated microgravity

Regenerative life support systems (RLSS) will play a vital role in achieving self-sufficiency during long-distance space travel. Urine conversion into a liquid nitrate-based fertilizer is a key process in most RLSS. This study describes the effects of simulated microgravity (SMG) on Comamonas testosteroni, Nitrosomonas europaea, Nitrobacter winogradskyi and a tripartite culture of the three, in the context of nitrogen recovery for the Micro-Ecological Life Support System Alternative (MELiSSA). Rotary cell culture systems (RCCS) and random positioning machines (RPM) were used as SMG analogues. The transcriptional responses of the cultures were elucidated. For CO2-producing C. testosteroni and the tripartite culture, a PermaLifeTM PL-70 cell culture bag mounted on an in-house 3D-printed holder was applied to eliminate air bubble formation during SMG cultivation. Gene expression changes indicated that the fluid dynamics in SMG caused nutrient and O2 limitation. Genes involved in urea hydrolysis and nitrification were minimally affected, while denitrification-related gene expression was increased. The findings highlight potential challenges for nitrogen recovery in space.

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.

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.

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.