Photobioreactors in Life Support Systems

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

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

The influence of gravity and light on locomotion and orientation of Heterocypris incongruens and Notodromas monacha (Crustacea, Ostracoda)

For future manned long-d uration space missions, the supply of essentials, such as food, water, and oxygen with the least possible material resupply from Earth is vital. This need could be satisfied utilizing aquatic bioregenerative life support systems (BLSS), as they facilitate recycling and autochthonous production. However, few organisms can cope with the instable environmental conditions and organic pollution potentially prevailing in such BLSS. Ostracoda, however, occur in eu- and even hypertrophic waters, tolerate organic and chemical waste, varying temperatures, salinity, and pH ranges. Thus, according to their natural role, they can link oxygen liberating, autotrophic algae, and higher trophic levels (e.g., fish) probably also in such harsh BLSS. Yet, little is known about how microgravity (µg) affects Ostracoda. In this regard, we investigated locomotion and orientation, as they are involved in locating mating partners and suitable microhabitats, foraging, and escaping predators. Our study shows that Ostracoda exhibit altered activity patterns and locomotion behavior (looping) in µg. The alterations are differentially marked between the studied species (i.e., 2% looping in Notodromas monacha, ~50% in Heterocypris incongruens) and also the thresholds of gravity perception are distinct, although the reasons for these differences remain speculative. Furthermore, neither species acclimates to µg nor orientates by light in µg. However, Ostracoda are still promising candidates for BLSS due to the low looping rate of N. monacha and our findings that the so far analyzed vital functions and life-history parameters of H. incongruens remained similar as under normal gravity conditions despite of its high looping rate.

Despite disorientation in microgravity, seed shrimp could form part of the food chain in artificial ecosystems designed for space missions. Jessica Fischer and Christian Laforsch of Germany’s University of Bayreuth investigated how simulated microgravity changed the movement of two species of seed shrimp (Ostracoda). Ostracoda can cope in unstable conditions and are being considered as food for fish in aquatic bioregenerative life support systems (BLSS) in manned space missions. Fish fed on Ostracoda that eat algae in these systems could form an important source of proteins for humans. Notodromas monacha and Heterocypris incongruens moved around in loops when exposed to simulated microgravity, but N. monacha did not loop as much. Looping movements suggest that gravity is an important orientational cue. Previous studies showed Ostracoda survived and reproduced successfully for months in space despite their looping behavior. Further studies are needed on N. monacha, since its low looping behavior could mean lower energy consumption making it better qualified for BLSS.