Deep continental subsurface is defined as oligotrophic environments where microorganisms present a very low metabolic rate. To date, due to the energetic cost of production and maintenance of ...biofilms, their existence has not been considered in poor porous subsurface rocks. We applied fluorescence in situ hybridization techniques and confocal laser scanning microscopy in samples from a continental deep drilling project to analyze the prokaryotic diversity and distribution and the possible existence of biofilms. Our results show the existence of natural microbial biofilms at all checked depths of the Iberian Pyrite Belt (IPB) subsurface and the co-occurrence of bacteria and archaea in this environment. This observation suggests that multi-species biofilms may be a common and widespread lifestyle in subsurface environments.
Viable cyanobacteria in the deep continental subsurface Puente-Sánchez, Fernando; Arce-Rodríguez, Alejandro; Oggerin, Monike ...
Proceedings of the National Academy of Sciences - PNAS,
10/2018, Volume:
115, Issue:
42
Journal Article
Peer reviewed
Open access
Cyanobacteria are ecologically versatile microorganisms inhabiting most environments, ranging from marine systems to arid deserts. Although they possess several pathways for light-independent energy ...generation, until now their ecological range appeared to be restricted to environments with at least occasional exposure to sunlight. Here we present molecular, microscopic, and metagenomic evidence that cyanobacteria predominate in deep subsurface rock samples from the Iberian Pyrite Belt Mars analog (southwestern Spain). Metagenomics showed the potential for a hydrogen-based lithoautotrophic cyanobacterial metabolism. Collectively, our results suggest that they may play an important role as primary producers within the deep-Earth biosphere. Our description of this previously unknown ecological niche for cyanobacteria paves the way for models on their origin and evolution, as well as on their potential presence in current or primitive biospheres in other planetary bodies, and on the extant, primitive, and putative extraterrestrial biospheres.
The discovery that most of the prokaryotic diversity and biomass on Earth resides in the deep subsurface, calls for an improved definition of habitability, which should consider the existence of dark ...biospheres in other planets and moons of the Solar System and beyond. The discovery of “interior liquid water worlds” on some ice moons with waterless surfaces has piqued wide astrobiological interest, but the sporadic mentions of the possibility of life in the deep subsurface of rocky planets in recent habitability reviews calls for a methodical effort to develop sufficient knowledge, both scientific and technological, to include the dark biospheres in our habitability assessments. In this review we analyze recent developments and the methodologies employed to characterize Earth’s continental hard rock deep subsurface to both prepare the future exploration of the putative dark biosphere of Mars and to highlight its importance when evaluating planetary habitability.
The preservation of biosignatures on Mars is largely associated with extensive deposits of clays formed under mild early Noachian conditions (> 3.9 Ga). They were followed by widespread precipitation ...of acidic sulfates considered adverse for biomolecule preservation. In this paper, an exhaustive mass spectrometry investigation of ferric subsurface materials in the Rio Tinto gossan deposit (~ 25 Ma) provides evidence of well-preserved molecular biosignatures under oxidative and acidic conditions. Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis shows a direct association between physical-templating biological structures and molecular biosignatures. This relation implies that the quality of molecular preservation is exceptional and provides information on microbial life formerly operating in the shallow regions of the Rio Tinto subsurface. Consequently, low-pH oxidative environments on Mars could also record molecular information about ancient life in the same way as the Noachian clay-rich deposits.
The Iberian Pyrite Belt (IPB) hosts one of the world's largest accumulations of acidic mine wastes and pit lakes. The mineralogical and textural characteristics of the IPB ores have favored the ...oxidation and dissolution of metallic sulfides, mainly pyrite, and the subsequent formation of acidic mining drainages. This work reports the physical properties, hydrogeochemical characteristics, and microbial diversity of two pit lakes located in the IPB. Both pit lakes are acidic and showed high concentrations of sulfate and dissolved metals. Concentrations of sulfate and heavy metals were higher in the Nuestra Señora del Carmen lake (NSC) by one order of magnitude than in the Concepción (CN) lake. The hydrochemical characteristics of NSC were typical of acid mine waters and can be compared with other acidic environments. When compared to other IPB acidic pit lakes, the superficial water of CN is more diluted than that of any of the others due, probably, to the strong influence of runoff water. Both pit lakes showed chemical and thermal stratification with well defined chemoclines. One particular characteristic of NSC is that it has developed a chemocline very close to the surface (2 m depth). Microbial community composition of the water column was analyzed by 16S and 18S rRNA gene cloning and sequencing. The microorganisms detected in NSC were characteristic of acid mine drainage (AMD), including iron oxidizing bacteria (Leptospirillum, Acidithiobacillus ferrooxidans) and facultative iron reducing bacteria and archaea (Acidithiobacillus ferrooxidans, Acidiphilium, Actinobacteria, Acidimicrobiales, Ferroplasma) detected in the bottom layer. Diversity in CN was higher than in NSC. Microorganisms known from AMD systems (Acidiphilium, Acidobacteria and Ferrovum) and microorganisms never reported from AMD systems were identified. Taking into consideration the hydrochemical characteristics of these pit lakes and the spatial distribution of the identified microorganisms, a model explaining their geomicrobiology is advanced.
The Dallol geothermal area in the northern part of the Danakil Depression (up to 124-155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being ...part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars.
The Bacillus xiamenensis RT6 strain was isolated and identified by morphological, biochemical and molecular tests from an extreme acidic environment, Rio Tinto (Huelva). Optimisation tests for ...exopolysaccharide (EPS) production in different culture media determined that the best medium was a minimal medium with glucose as the only carbon source. The exopolymer (EPSt) produced by the strain was isolated and characterised using different techniques (GC-MS, HPLC/MSMS, ATR-FTIR, TGA, DSC). The molecular weight of EPSt was estimated. The results showed that the average molecular weight of EPSt was approximately 2.71 × 104 Da and was made up of a heteropolysaccharide composed of glucose (60%), mannose (20%) and galactose (20%). The EPSt showed antioxidant capabilities that significantly improved cell viability. Metal chelation determined that EPSt could reduce the concentration of transition metals such as iron at the highest concentrations tested. Finally, the emulsification study showed that EPSt was able to emulsify different natural polysaccharide oils, reaching up to an 80% efficiency (olive and sesame oil), and was a good candidate for the substitution of the most polluting emulsifiers. The EPSt was found to be suitable for pharmaceutical and industrial applications.
A specific microorganism, Pantoea agglomerans uam8, was isolated from the ionic liquid (IL) Choline NTF2 and identified by molecular biology. A biodegradation study was performed at osmolarity ...conditions (0.2, 0.6, 1.0 M). These had an important influence on the growth of the strain, exopolysaccharide (EPS) production, and biodegradation (1303 mg/L max production and 80% biodegradation at 0.6 M). These conditions also had an important influence on the morphology of the strain and its EPSs, but not in the chemical composition. The EPS (glucose, mannose and galactose (6:0.5:2)) produced at 0.6 M was further characterized using different techniques. The obtained EPSs presented important differences in the behavior of the emulsifying activity for vegetable oils (olive (86%), sunflower (56%) and coconut (90%)) and hydrocarbons (diesel (62%), hexane (60%)), and were compared with commercial emulsifiers. The EPS produced at 0.6 M had the highest emulsifying activity overall. This EPS did not show cytotoxicity against the tested cell line (<20%) and presented great advantages as an antioxidant (1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) (85%), hydroxyl radical (OH) (99%), superoxide anion (O2−) (94%), chelator (54%), and antimicrobial product (15 mm). The osmolarity conditions directly affected the capacity of the strain to biodegrade IL and the subsequently produced EPS. Furthermore, the EPS produced at 0.6 M has potential for environmental applications, such as the removal of hazardous materials by emulsification, whilst resulting in positive health effects such as antioxidant activity and non-toxicity.
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