Astrovirology: how viruses enhance our understanding of life in the Universe.

Viruses are the most numerically abundant biological entities on Earth. As ubiquitous replicators of molecular information and agents of community change, viruses have potent effects on the life on Earth, and may play a critical role in human spaceflight, for life-detection missions to other planetary bodies and planetary protection. However, major knowledge gaps constrain our understanding of the Earth's virosphere: (1) the role viruses play in biogeochemical cycles, (2) the origin(s) of viruses and (3) the involvement of viruses in the evolution, distribution and persistence of life. As viruses are the only replicators that span all known types of nucleic acids, an expanded experimental and theoretical toolbox built for Earth's viruses will be pivotal for detecting and understanding life on Earth and beyond. Only by filling in these knowledge and technical gaps we will obtain an inclusive assessment of how to distinguish and detect life on other planetary surfaces. Meanwhile, space exploration requires life-support systems for the needs of humans, plants and their microbial inhabitants. Viral effects on microbes and plants are essential for Earth's biosphere and human health, but virus-host interactions in spaceflight are poorly understood. Viral relationships with their hosts respond to environmental changes in complex ways which are difficult to predict by extrapolating from Earth-based proxies. These relationships should be studied in space to fully understand how spaceflight will modulate viral impacts on human health and life-support systems, including microbiomes. In this review, we address key questions that must be examined to incorporate viruses into Earth system models, life-support systems and life detection. Tackling these questions will benefit our efforts to develop planetary protection protocols and further our understanding of viruses in astrobiology.

Effect of air nanobubbles on oxygen transfer, oxygen uptake, and diversity of aerobic microbial consortium in activated sludge reactors.

Nanobubbles have the potential to curtail the loss of oxygen during activated sludge aeration due to their extensive surface areas and lack of buoyance in solution. In this study, nanobubble aeration was explored as a novel approach to enhance aerobic activated sludge treatment and benchmarked against coarse bubble aeration at the lab scale. Nanobubble aerated activated sludge reactors achieved greater dissolved oxygen levels at faster rates. Higher soluble chemical oxygen demand removal by 10% was observed when compared to coarse bubble aeration with the same amount of air. The activated sludge produced compact sludge yielding easier waste sludge for subsequent sludge handling. The samples showed fewer filamentous bacteria with a lower relative abundance of floc forming Corynebacterium, Pseudomonas, and Zoogloea in the sludge. The microbiome of the nanobubble-treated activated sludge showed significant shifts in the abundance of community members at the genus level and significantly lower alpha and beta diversities.

Supporting Simultaneous Air Revitalization and Thermal Control in a Crewed Habitat With Temperate Chlorella vulgaris and Eurythermic Antarctic Chlorophyta.

Including a multifunctional, bioregenerative algal photobioreactor for simultaneous air revitalization and thermal control may aid in carbon loop closure for long-duration surface habitats. However, using water-based algal media as a cabin heat sink may expose the contained culture to a dynamic, low temperature environment. Including psychrotolerant microalgae, native to these temperature regimes, in the photobioreactor may contribute to system stability. This paper assesses the impact of a cycled temperature environment, reflective of spacecraft thermal loops, to the oxygen provision capability of temperate Chlorella vulgaris and eurythermic Antarctic Chlorophyta. The tested 28-min temperature cycles reflected the internal thermal control loops of the International Space Station (C. vulgaris, 9-27°C; Chlorophyta-Ant, 4-14°C) and included a constant temperature control (10°C). Both sample types of the cycled temperature condition concluded with increased oxygen production rates (C. vulgaris; initial: 0.013 mgO2 L-1, final: 3.15 mgO2 L-1 and Chlorophyta-Ant; initial: 0.653 mgO2 L-1, final: 1.03 mgO2 L-1) and culture growth, suggesting environmental acclimation. Antarctic sample conditions exhibited increases or sustainment of oxygen production rates normalized by biomass dry weight, while both C. vulgaris sample conditions decreased oxygen production per biomass. However, even with the temperature-induced reduction, cycled temperature C. vulgaris had a significantly higher normalized oxygen production rate than Antarctic Chlorophyta. Chlorophyll fluorometry measurements showed that the cycled temperature conditions did not overly stress both sample types (FV/FM: 0.6-0.75), but the Antarctic Chlorophyta sample had significantly higher fluorometry readings than its C. vulgaris counterpart (F = 6.26, P < 0.05). The steady state C. vulgaris condition had significantly lower fluorometry readings than all other conditions (FV/FM: 0.34), suggesting a stressed culture. This study compares the results to similar experiments conducted in steady state or diurnally cycled temperature conditions. Recommendations for surface system implementation are based off the presented results. The preliminary findings imply that both C. vulgaris and Antarctic Chlorophyta can withstand the dynamic temperature environment reflective of a thermal control loop and these data can be used for future design models.

Effects of stepwise changes in dissolved carbon dioxide concentrations on metabolic activity in Chlorella for spaceflight applications.

This paper assesses the impacts to the growth rate, health, oxygen production, and carbon dioxide fixation and nitrogen assimilation of Chlorella vulgaris while sparging the culture with various influent concentrations of carbon dioxide. Selected concentrations reflect a cabin environment with one crew member (0.12% v/v) and four crew members (0.45% v/v). Stepwise, sustained changes in influent carbon dioxide concentration on day four of the eight-day experiments simulated a dynamic crew size, reflective of a planetary surface mission. Control experiments used constant influent concentrations across eight days. Significant changes in growth rate (0.12%-to-0.45%: 57% increase; 0.45%-to-0.12%: 59% reduction) suggest a positive correlation between metabolic activity of C. vulgaris and environmental carbon dioxide concentration. Statistical tests illustrate that algae are more sensitive to reductions in influent carbon dioxide. No specific correlation of the nitrogen assimilation rate to influent carbon dioxide, suggesting a nitrogen-limited or irradiance-limited system. Photosynthetic yield results (0.59-0.72) indicate that the culture was minimally stressed in all tested conditions. This paper compares these results to findings of published, steady-state experiments conducted under similar carbon dioxide environments. The findings presented here imply that a sufficient volume of C. vulgaris, with nutrient supplementation or biomass harvesting, could support the respiratory requirements of a long duration human mission with a dynamic cabin environment and these data can be used in future dynamic models.

Failure modes, causes, and effects of algal photobioreactors used to control a spacecraft environment.

Bioregenerative technologies, in particular algae photobioreactors, have the potential to provide closed-loop environmental control and life support for human space flight, if robust enough for long-duration deep space missions. This paper reviews the failure modes, causes, and effects of an algal photobioreactor system for use in space flight environmental control and life support applications. The likelihood and severity for each failure is estimated, and associated mitigation or contingency plans are described. Failure modes can stem from either the algae cellular physiology or the engineered system needed for the application and are grouped in this paper accordingly.