Roberto Barbieri

Potential Fossil Endoliths in Vesicular Pillow Basalt, Coral Patch Seamount, Eastern North Atlantic Ocean

The chilled rinds of pillow basalt from the Ampère-Coral Patch Seamounts in the eastern North Atlantic were studied as a potential habitat of microbial life. A variety of putative biogenic structures, which include filamentous and spherical microfossil-like structures, were detected in K-phillipsite-filled amygdules within the chilled rinds. The filamentous structures (∼2.5 μm in diameter) occur as K-phillipsite tubules surrounded by an Fe-oxyhydroxide (lepidocrocite) rich membranous structure, whereas the spherical structures (from 4 to 2 μm in diameter) are associated with Ti oxide (anatase) and carbonaceous matter. Several lines of evidence indicate that the microfossil-like structures in the pillow basalt are the fossilized remains of microorganisms. Possible biosignatures include the carbonaceous nature of the spherical structures, their size distributions and morphology, the presence and distribution of native fluorescence, mineralogical and chemical composition, and environmental context. When taken together, the suite of possible biosignatures supports the hypothesis that the fossil-like structures are of biological origin. The vesicular microhabitat of the rock matrix is likely to have hosted a cryptoendolithic microbial community. This study documents a variety of evidence for past microbial life in a hitherto poorly investigated and underestimated microenvironment, as represented by the amygdules in the chilled pillow basalt rinds. This kind of endolithic volcanic habitat would have been common on the early rocky planets in our Solar System, such as Earth and Mars. This study provides a framework for evaluating traces of past life in vesicular pillow basalts, regardless of whether they occur on early Earth or Mars.

Biomarkers of endolithic communities within gypsum crusts (Southern Tunisia).

Evaporite accumulations produced by artesian waters in the arid zones of southern Tunisia led to the formation of subrounded, gypsiferous mounds consisting of irregular alternations of mineral precipitates and aeolian sand. The joint occurrence of gypsum crusts and plant colonization determined the stabilization of their top surface. Careful examination of the pigmented (green-brown) crusts revealed endolithic microbial communities just below the surface. In previous optical and scanning electron microscope studies cyanobacteria were the dominant component of these communities. Molecular diversity studies based on small subunit ribosomal RNA (SSU rRNA) gene analysis revealed that Flavobacteria, Actinobacteria, Deinococcales, Alpha- and Gamma- Proteobacteria are also important components of the microbial assemblage. Their pigment analyses, determined by high performance liquid chromatography (HPLC), detected the presence of carotenoids and chlorophyll (chl) a and b. Microbial communities that produce pigmentation and display an endolithic lifestyle typify the extreme environments as those found in arid/semiarid and hot desert regions.

Physicochemical Conditions and Microbial Diversity Associated with the Evaporite Deposits in the Laguna de la Piedra (Salar de Atacama, Chile)

The Salar de Atacama, located in Northern Chile, is a wide salt flat that is characterized by several salt lakes, which are locally called lagunas. The Laguna de la Piedra is one of the salt lake systems that is located in the northernmost sector of the Salar de Atacama. The present paper examines some physicochemical properties of the Laguna de la Piedra as well as the microbial diversity of the evaporite deposits. Under extreme desiccation and ambient UV flux, the evaporite deposits can create favorable endolithic microniches for the development of microorganisms. In the Laguna de la Piedra these deposits host a variety of halophilic microorganisms, which were investigated by using an optical and environmental scanning electron microscope (ESEM) as well as molecular diversity studies based on the small subunit ribosomal (SSU) rRNA of Bacteria, Archaea and Eucarya. We detected a single phylotype of halophilic archaea and a oxytrichid ciliate. Within the bacteria, a variety of Cyanobacteria, Bacteroidetes, Alpha-, Beta- and Deltaproteobacteria, as well as members of the candidate division TM6, were identified.

Endoliths in Terrestrial Arid Environments: Implications for Astrobiology

Microbial life in hot and cold desert environments inhabits endolithic niches. The endolithic microorganisms include bacteria, fungi and lichens. To protect themselves from the inhospitable conditions, such as high UV radiation, dryness, and rapid temperature variations, microorganisms migrate into fractures or in pore spaces where the necessary nutrient, moisture, and light are sufficient for survival. Examples of endolithic communities are well documented from the Negev Desert, Antarctica and the Artic regions, and the Atacama Desert. The most common substrates are porous, crystalline sandstones with calcium carbonate cements and sulfate (gypsum) and other evaporite mineral crusts. The detection of sulfate on the Martian surface has sparked off considerable interest in the astrobiological potential of the evaporite deposits of continental environments, which may potentially host (or may have hosted) endolithic microorganisms.

Fossil Microorganisms at Methane Seeps: An Astrobiological Perspective

The recent detection of methane in the martian atmosphere has stimulated a debate on its source, including speculations on a possible biological origin as in the Earth’s atmosphere, where methane is present as a trace gas and is mostly produced by life. Large amounts of methane seepage flows from the subsurface are documented on Earth since the lower Paleozoic by the formation of authigenic carbonate deposits. Methane-derived carbonates also precipitate in the modern continental slopes throughout the world with a great variety in size and shape, and document a still active methane advection from deep sources. The interest of seep carbonates in an astrobiological perspective relies on their relationship with microbiological communities that inhabit the methane seep ecosystems and establish the base of their food chain. They also might represent terrestrial analogues for martian environments and possible models for microbial life on other planets.