The Mars 2020 mission will seek the signs of ancient life on Mars and will identify, prepare, document, and cache a set of samples for possible return to Earth by a follow-on mission. Mars 2020 and its Perseverance rover thus link and further two long-held goals inThe Mars 2020 Mission Edited by Kenneth A
The permanent ice cover of Lake Vida (Antarctica) encapsulates an extreme cryogenic brine ecosystem (−13°C; salinity, 200). This aphotic ecosystem is anoxic and consists of a slightly acidic (pH 6.2) sodium chloride-dominated brine. Expeditions in 2005 and 2010 were conducted to investigate the biogeochemistry of Lake Vida's brine system. A phylogenetically diverse and metabolically active Bacteria dominated microbial assemblage was observed in the brine. These bacteria live under very high levels of reduced metals, ammonia, molecular hydrogen (H 2 ), and dissolved organic carbon, as well as high concentrations of oxidized species of nitrogen (i.e., supersaturated nitrous oxide and ∼1 mmol·L −1 nitrate) and sulfur (as sulfate). The existence of this system, with active biota, and a suite of reduced as well as oxidized compounds, is unusual given the millennial scale of its isolation from external sources of energy. The geochemistry of the brine suggests that abiotic brine-rock reactions may occur in this system and that the rich sources of dissolved electron acceptors prevent sulfate reduction and methanogenesis from being energetically favorable. The discovery of this ecosystem and the in situ biotic and abiotic processes occurring at low temperature provides a tractable system to study habitability of isolated terrestrial cryoenvironments (e.g., permafrost cryopegs and subglacial ecosystems), and is a potential analog for habitats on other icy worlds where water-rock reactions may cooccur with saline deposits and subsurface oceans.astrobiology | geomicrobiology | microbial ecology | extreme environment T he observation of microbes surviving and growing in a variety of icy systems on Earth has expanded our understanding of how life pervades, functions, and persists under challenging conditions (e.g., refs. 1-3). Studies of the physical characteristics, the geochemical properties, and microbes in ice (triple point junctions, brine channels, gas bubbles) have also changed our perceptions of the environments that may contain traces of, or even sustain, life beyond Earth [e.g., Mars (4), Europa (5), and Enceladus (6)].Solute depression of ice crystal formation or solar radiation melting of water ice are key processes that provide liquid waterthe key solvent that makes life possible-within icy systems. Microbial communities in these conditions are often sustained by a supply of energy that ultimately derives from photosynthesis (present or past). The understanding of ecosystems based on energy sources other than the Sun comes mainly from realms where hydrothermal processes have provided reduced compounds necessary to fuel chemosynthetically driven ecosystems. Methane derived from thermogenic or biogenic sources can also support microbial communities in deep sea (7) and high arctic cold saline seeps (8). More recently, discoveries of life and associated processes in deep terrestrial subsurface ecosystems (9) provide compelling evidence of subsurface life that in some cases is fueled by nonphotosynthetic processes. Ou...
[1] Surface and subsurface soil samples analyzed for this investigation were collected from the hyperarid Yungay region in the Atacama Desert, Chile. This report details the bacterial diversity derived from DNA and PLFA extracted directly from these extremely desiccated soils. Actinobacteria, Proteobacteria, Firmicutes and TM7 division bacteria were detected. Ninety-four percent of the 16S rRNA genes cloned from these soils belong to the Actinobacteria phylum, and the majority of these were most closely related to the genus Frankia. A 24-hour water activity (a w ) time course showed a diurnal cycle that peaked at 0.52 in the early predawn hours, and ranged from 0.01-0.08 during the day. All measured water activity values were below the levels required for microbial growth or enzyme activity. Total organic carbon (TOC) concentrations were above the limit of detection and below the limit of quantification (i.e., 200 mg/g < TOC < 1000 mg/g), and phospholipid fatty acid (PLFA) concentrations ranged from 2 Â 10 5 to 7 Â 10 6 cell equivalents per gram of soil. Soil extracts analyzed for culturable biomass yielded mostly no growth on R2A media; the highest single extract yielded 47 colony forming units (CFU) per gram of soil.Citation: Connon, S.
The luminescence lifetime of Ru(tpy) 2 2+ (tpy ) 2,2′:6,2′′-terpyridine) is 8.0 µs in H 2 SO 4 /H 2 O and HSO 3 F/H 2 O glasses (25% v/v) at 77 K, and 10.2 µs in D 2 SO 4 /D 2 O (25% v/v). Addition of moderate concentrations of the powerfully oxidizing Fe(OH 2 ) 6 3+ ion to the glasses leads to accelerated and highly nonexponential *Ru(tpy) 2 2+ decay kinetics. The quenching is attributed to electron transfer from *Ru(tpy) 2 2+ to randomly dispersed Fe(OH 2 ) 6 3+ complexes. The luminescence decay kinetics and quantum yields in the three aqueous glasses indicate that the electron-transfer rate constants decrease from ∼10 13 s -1 at van der Waals contact with an exponential distance decay constant of 1.68 ( 0.07 Å -1 .
Experimental Section.Materials. DPA (dipicolinic acid) was purchased from Sigma-Aldrich and used as received.TbCl 3 was purchased from Alfa Aesar and used as received. DO2A (1,4,7,10-tetraazacyclododecane-1,7-diacetate) was obtained after hydrolysis (see reference 11) of DO2A-tBu-ester (1,4,7,10-tetraazacyclododecane-1,7-di(t-butyl acetate)), purchased from Macrocyclics.
The detection of bacterial spores via dipicolinate-triggered lanthanide luminescence has been improved in terms of detection limit, stability, and susceptibility to interferents by use of lanthanidemacrocycle binary complexes. Specifically, we compared the effectiveness of Sm, Eu, Tb and Dy complexes with the macrocycle 1, 4,7, to the corresponding lanthanide aquo ions. The Ln(DO2A) + binary complexes bind dipicolinic acid (DPA), a major constituent of bacterial spores, with greater affinity and demonstrate significant improvement in bacterial spore detection. Of the four luminescent lanthanides studied, the terbium complex exhibits the greatest dipicolinate binding affinity (100-fold greater than Tb 3+ alone, and 10-fold greater than other Ln(DO2A) + complexes) and highest quantum yield. Moreover, the inclusion of DO2A extends the pH range over which Tb-DPA coordination is stable, reduces the interference of calcium ions nearly 5-fold, and mitigates phosphate interference 1000-fold compared to free terbium alone. In addition, detection of Bacillus atrophaeus bacterial spores was improved by the use of Tb (DO2A) + , yielding a 3-fold increase in the signal-to-noise ratio over Tb 3+ . Out of the eight cases investigated, the Tb(DO2A) + binary complex is best for the detection of bacterial spores.
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