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Beneath Enceladus' ice crust lies an ocean which might host habitable conditions. Here, the scale and productivity of a notional Enceladean methanogenic biosphere are computed as a function of the core‐to‐ocean flux of hydrogen and the ratio between abiotic and biotic methane in Enceladus' space plume. Habitats with an ocean‐top pH range of 8–9 have up to 40%–60% probability of being energy‐limited. Those at pH > 9 are increasingly uninhabitable, and those <8.5 are increasingly likely to host exponential growth, possibly leading to compositional inconsistencies between the ocean and Cassini gas observations. In those cases, energy‐based habitability models cannot infer an inhabited Enceladus consistent with both Earth life and Cassini measurements without including additional microbial growth limiters such as nutrient limitation, toxicity, or spatial constraints. If methanogens are isolated to a 350 K seafloor habitat and consume 10 mol s−1 of H2, the most probable biomass is 103, 103.7 kg C with ocean‐top pH 8,9, respectively. Biomass production consistent with space plume fluxes is 104–106 kgC yr−1—milligrams of cellular carbon per kilogram of H2O ejected—but requires that >50% of the space plume methane is biotic. Alternative scenarios are presented, and biomass is generally lower when habitat temperature is higher. Ocean biomass density cannot yet be reliably estimated owing to uncertainties in the scale and physicochemical properties of Enceladus' putative habitats. Evaluating abiotic to biotic ratios in plume methane and organic material could help identify false negative results from life detection missions and constrain the scale of an underlying biosphere. Plain Language Summary: The Cassini spacecraft observed energy and nutrient sources for life erupting from a water ocean below the icy exterior of Saturn's moon Enceladus. Future spacecraft planned for Enceladus, Europa and Titan will obtain similar measurements in greater detail. In this work, we calculate the probability that different suites of environments inside Enceladus' ocean are habitable for methanogens, an ancient type of organism which may be able to survive there. Three scenarios are possible: uninhabitable, habitable, and energy‐saturated. Next, we extend this calculation to show that the possible biosphere is small but productive. Microbial waste, generated at the seafloor, could be ejected from the ocean and consequently snow down onto Enceladus' surface. Mass spectrometers on future spacecraft could constrain these possibilities further and may be critical to inferring biosignatures when cell densities are too low to detect. Key Points: Spatial habitability on Enceladus is not guaranteed, and additional modeling parameters are needed to evaluate possible vacant habitatsCell turnover is important for life detection missions and can be constrained more tightly than total biomassAbiotic to biotic ratios of space plume carbon are critical as biosignatures and for assessing the scale of Enceladus' notional biosphere [ABSTRACT FROM AUTHOR]

In recent years, Enceladus' subsurface ocean has become a tantalizing case study for potentially habitable conditions in an extraterrestrial ocean world. However, we still know very little about its subsurface conditions. Its oceanic composition is difficult to characterize with current data and estimates are highly dependent on model‐based interpretations which are also not yet tightly constrained. In light of these uncertainties, we consider a wide selection of the inferred parameter spaces to quantify the energy available to putative hydrogenotrophic methanogens on Enceladus in the bulk ocean at cool and elevated temperatures. We estimate the instantaneous power supply their metabolism could provide in these conditions and compare it to the expected power demands of life on Earth. To be habitable for methanogens a 273 K ocean with relatively high salt content must have pH < 10, and a relatively low salt ocean must have pH < 8 at 273 K, or pH < 9 when heated to >360 K. Some combinations meet the power demands of exponential growth, but large swathes of the parameter space appear energetically uninhabitable. The habitability of the Enceladus ocean for methanogens appears to be a delicate balance between its temperature, pH, salinity, and concentrations of carbonates, nutrients, and dissolved gases (particularly H2). Many of these parameters are co‐dependent; variation in any one of them could tip the balance into uninhabitable conditions. Further constraining these variables should be a priority for future missions to ocean worlds to enable definitive assessments of their habitability. Plain Language Summary: Observations of Enceladus in recent years have revealed tantalizing details of its potentially habitable subsurface ocean, allowing its conditions to be resolved in unprecedented detail compared to other icy moons. Still, the variation in possible parameters below its icy shell is huge, ranging from the cold bulk ocean with a pH similar to seawater on Earth to potentially scalding alkaline fluids at its depths. The ocean contains the ingredients of an ancient metabolism that is used by life on Earth by organisms known as methanogens. In this study, we explore the instantaneous habitability of Enceladus' subsurface ocean to methanogens using a range of environmental parameters informed by data from the Cassini mission and modeling. In other words, we ask: if Cassini's observations offered a "snapshot" view of the ocean, does a habitable window exist within the uncertainty of the data, without considering as‐yet unconstrained (but still important) variables such as a supply of nutrients? Some parameter combinations appear habitable, but not all the combinations are suitable for methanogens as we know them on Earth. We identify the most important drivers of habitability in Enceladus' ocean and explain how they can be better constrained by future research or space missions. Key Points: •Key known drivers of the Enceladus ocean's habitability with respect to methanogens are identified and their uncertainties accounted for•There is energy available for methanogens in most cases if the pH of the bulk ocean is less than 10•Instantaneous microbial power supplies imply both habitable and uninhabitable conditions are possible [ABSTRACT FROM AUTHOR]

Summary: We have recently argued that, because microbes have pervasive – often vital – influences on our lives, and that therefore their roles must be taken into account in many of the decisions we face, society must become microbiology‐literate, through the introduction of relevant microbiology topics in school curricula (Timmis et al. 2019. Environ Microbiol21: 1513‐1528). The current coronavirus pandemic is a stark example of why microbiology literacy is such a crucial enabler of informed policy decisions, particularly those involving preparedness of public‐health systems for disease outbreaks and pandemics. However, a significant barrier to attaining widespread appreciation of microbial contributions to our well‐being and that of the planet is the fact that microbes are seldom visible: most people are only peripherally aware of them, except when they fall ill with an infection. And it is disease, rather than all of the positive activities mediated by microbes, that colours public perception of 'germs' and endows them with their poor image. It is imperative to render microbes visible, to give them life and form for children (and adults), and to counter prevalent misconceptions, through exposure to imagination‐capturing images of microbes and examples of their beneficial outputs, accompanied by a balanced narrative. This will engender automatic mental associations between everyday information inputs, as well as visual, olfactory and tactile experiences, on the one hand, and the responsible microbes/microbial communities, on the other hand. Such associations, in turn, will promote awareness of microbes and of the many positive and vital consequences of their actions, and facilitate and encourage incorporation of such consequences into relevant decision‐making processes. While teaching microbiology topics in primary and secondary school is key to this objective, a strategic programme to expose children directly and personally to natural and managed microbial processes, and the results of their actions, through carefully planned class excursions to local venues, can be instrumental in bringing microbes to life for children and, collaterally, their families. In order to encourage the embedding of microbiology‐centric class excursions in current curricula, we suggest and illustrate here some possibilities relating to the topics of food (a favourite pre‐occupation of most children), agriculture (together with horticulture and aquaculture), health and medicine, the environment and biotechnology. And, although not all of the microbially relevant infrastructure will be within reach of schools, there is usually access to a market, local food store, wastewater treatment plant, farm, surface water body, etc., all of which can provide opportunities to explore microbiology in action. If children sometimes consider the present to be mundane, even boring, they are usually excited with both the past and the future so, where possible, visits to local museums (the past) and research institutions advancing knowledge frontiers (the future) are strongly recommended, as is a tapping into the natural enthusiasm of local researchers to leverage the educational value of excursions and virtual excursions. Children are also fascinated by the unknown, so, paradoxically, the invisibility of microbes makes them especially fascinating objects for visualization and exploration. In outlining some of the options for microbiology excursions, providing suggestions for discussion topics and considering their educational value, we strive to extend the vistas of current class excursions and to: (i) inspire teachers and school managers to incorporate more microbiology excursions into curricula; (ii) encourage microbiologists to support school excursions and generally get involved in bringing microbes to life for children; (iii) urge leaders of organizations (biopharma, food industries, universities, etc.) to give school outreach activities a more prominent place in their mission portfolios, and (iv) convey to policymakers the benefits of providing schools with funds, materials and flexibility for educational endeavours beyond the classroom. [ABSTRACT FROM AUTHOR]

Summary: Environmental cues that regulate motility are poorly understood, but specific carbon and nitrogen sources, such as casamino acids (CAA), are known to stimulate motility in model organisms. However, natural environments are commonly more nutrient‐limited than laboratory growth media, and the effect of energy‐rich CAA on the motility of oligotrophic microorganisms is unknown. In this study, an extreme oligocarbotroph, Variovorax paradoxus YC1, was isolated from weathered shale rock within a disused mine level in North Yorkshire, UK. The addition of 0.1% CAA to minimal media significantly reduced the motility of YC1 after 72 h and inhibited swimming motility resulting in enhanced surface growth. We propose this response to CAA is a physiological adaptation to oligotrophy, facilitating the colonization of nutrient‐rich environments. [ABSTRACT FROM AUTHOR]

Abstract: NASA's Mars Science Laboratory mission has collected evidence of a long‐lasting habitable environment in the Sheepbed sediments of Gale Crater on Mars. The geochemistry of this mudstone suggests that the lake filling the crater in Mars' past had a neutral pH and low salinity and contained elements and redox couples required by life. We produced a geochemical analogue to the Sheepbed mudstone by mixing a collection of its primary minerals to match the X‐Ray diffraction data from Mars Science Laboratory. Here we describe the production of the Y‐Mars (Yellowknife‐Mars) analogue and characterize its properties, including the presence of background carbon, nitrogen, and sulfur. We highlight some of the unavoidable issues involved in making analogues, especially for astrobiological applications. The Y‐Mars analogue has a number of applications for astrobiological research, but more analogues are required to properly represent the diversity of Martian sedimentary contexts. [ABSTRACT FROM AUTHOR]

Interactions between microorganisms and rocks play an important role in Earth system processes. However, little is known about the molecular capabilities microorganisms require to live in rocky environments. Using a quantitative label-free proteomics approach, we show that a model bacterium ( C upriavidus metallidurans CH34) can use volcanic rock to satisfy some elemental requirements, resulting in increased rates of cell division in both magnesium- and iron-limited media. However, the rocks also introduced multiple new stresses via chemical changes associated with pH, elemental leaching and surface adsorption of nutrients that were reflected in the proteome. For example, the loss of bioavailable phosphorus was observed and resulted in the upregulation of diverse phosphate limitation proteins, which facilitate increase phosphate uptake and scavenging within the cell. Our results revealed that despite the provision of essential elements, rock chemistry drives complex metabolic reorganization within rock-dwelling organisms, requiring tight regulation of cellular processes at the protein level. This study advances our ability to identify key microbial responses that enable life to persist in rock environments. [ABSTRACT FROM AUTHOR]

Since a key requirement of known life forms is available water (water activity; aw), recent searches for signatures of past life in terrestrial and extraterrestrial environments have targeted places known to have contained significant quantities of biologically available water. However, early life on Earth inhabited high-salt environments, suggesting an ability to withstand low water-activity. The lower limit of water activity that enables cell division appears to be ~ 0.605 which, until now, was only known to be exhibited by a single eukaryote, the sugar-tolerant, fungal xerophile Xeromyces bisporus. The first forms of life on Earth were, though, prokaryotic. Recent evidence now indicates that some halophilic Archaea and Bacteria have water-activity limits more or less equal to those of X. bisporus. We discuss water activity in relation to the limits of Earth's present-day biosphere; the possibility of microbial multiplication by utilizing water from thin, aqueous films or non-liquid sources; whether prokaryotes were the first organisms able to multiply close to the 0.605-aw limit; and whether extraterrestrial aqueous milieux of ≥ 0.605 aw can resemble fertile microbial habitats found on Earth. [ABSTRACT FROM AUTHOR]

- Meteorite impacts, one of the most ubiquitous processes in the solar system, have the ability to destroy as well as create habitats for life. The impact process can increase the translucency and porosity of the target substrate, as well as mobilize biologically relevant elements within the substrate. For endolithic organisms, this process has important implications, especially in extreme environments where they are forced to seek refuge in the interior of rocks. Here, we show that unshocked target rocks and rocks that have experienced pressures up to about 80 GPa from the Haughton impact structure, Devon Island, Canada, possess a small, but discernible change in bulk chemistry within the major oxide analysis. However, changes in the distribution of elements did occur with increasing shock level for both the sedimentary and crystalline target. Both the crystalline and sedimentary target rocks contain significant amounts of glasses at higher shock levels (up to about 95% by volume), which would improve the availability of these elements to potential microbial endoliths as glasses are more easily dissolved by organic acids. The implication that impact events do not impoverish their capacity to serve as a 'substrate' through volatilization is important with respect to analogous impact structures on Mars. After the deleterious effects of the direct meteorite impact, any microorganisms on Mars would have benefited from the input of heat, the mobilization of a possible frozen groundwater system, as well as increased translucency, porosity, and trace nutrient availability of the target substrate. [ABSTRACT FROM AUTHOR]

Drylands are the largest terrestrial biome on Earth and a ubiquitous feature is desert pavement terrain, comprising rocks embedded in the mineral soil surface. Quartz and other translucent rocks are common and microbial communities termed hypoliths develop as biofilms on their ventral surfaces. In extreme deserts these represent major concentrations of biomass, and are emerging as key to geobiological processes and soil stabilization. These highly specialized communities are dominated by cyanobacteria that support diverse heterotrophic assemblages. Here we identify global-scale trends in the ecology of hypoliths that are strongly related to climate, particularly with regard to shifts in cyanobacterial assemblages. A synthesis of available data revealed a linear trend for colonization with regard to climate, and we suggest potential application for hypoliths as 'biomarkers' of aridity on a landscape scale. The potential to exploit the soil-stabilizing properties of hypolithic colonization in environmental engineering on dryland soils is also discussed. [ABSTRACT FROM AUTHOR]

Alteration textures were examined in subglacial (hyaloclastite) deposits at Valafell, Southern Iceland. Pitted and ‘elongate’ alteration features are observed in the glass similar to granular and tubular features reported previously in deep-ocean basaltic glasses, but elongate features generally did not have a length to width ratio greater than five. Elongate features were found in only 7% of surfaces. Crystalline basalt clasts, which are incorporated into the hyaloclastite, did not display elongate structures. Pitted alteration features were poorly defined in crystalline basalt, comprising only 4% of the surface compared to 47% in the case of basaltic glass. Examination of silica-rich glass (obsidian) and rhyolite similarly showed poorly defined pitted textures that comprised less than 15% of the surface and no elongate features were observed. These data highlight the differences in alteration textures between terrestrial basaltic glass and previously studied deep-ocean and subsurface basaltic glass, and the important role of mineralogy in controlling the type and abundance of alteration features. The hyaloclastite contains a diverse and abundant bacterial population, as determined by 16S rDNA analysis, which could be involved in weathering the glass. Despite the presence of phototrophs, we show that they were not involved in the production of most alteration textures in the basaltic glass materials we examined. [ABSTRACT FROM AUTHOR]

Discusses some of the biological and ecological characteristics of impact craters. Significance of impact crater biology; Common patterns in post-impact biological changes; Chronological sequence of post-impact ecology.

Discusses the characteristics of a wide variety of ultraviolet (UV)-screening compounds. Major bands of UV radiation; Advantages of passive UV screening; Implications for the development of artificial UV-screening methods to reduce human exposure to UV radiation.

The establishment of a permanent human settlement in space is one of humanity's ambitions. To achieve this, microorganisms will be used to carry out many functions such as recycling, food and pharmaceutical production, mining and other processes. However, the physical and chemical extremes in all locations beyond Earth exceed known growth limits of microbial life. Making microbes more tolerant of a greater range of extraterrestrial extremes will not produce organisms that can grow in unmodified extraterrestrial environments since in many of them not even liquid water can exist. However, by narrowing the gap, the engineering demands on bioindustrial processes can be reduced and greater robustness can be incorporated into the biological component. I identify and describe these required microbial biotechnological modifications and speculate on long-term possibilities such as microbial biotechnology on Saturn's moon Titan to support a human presence in the outer Solar System and bioprocessing of asteroids. A challenge for space microbial biotechnology in the coming decades is to narrow the microbial gap by systemically identifying the genes required to do this and incorporating them into microbial systems that can be used to carry out bioindustrial processes of interest., (© 2021 The Authors. Microbial Biotechnology published by Society for Applied Microbiology and John Wiley & Sons Ltd.)