Читать книгу EXTREMOPHILES as Astrobiological Models - Группа авторов - Страница 18

Richard L. Weiss Bizzoco* and Scott T. Kelley

Department of Biology, San Diego State University, San Diego, California, USA

Abstract

Following meteoric recharge, fundamental components of volcanic magma (heat, gases and ions) are carried by rising steam from the subsurface through porous and fractured passageways until the heated steam exits at the surface in caves and vents. Deposits accumulate as steam condenses on cooler cave ceilings and vent walls, leaving evaporites, precipitates, sublimates, and particulates in solid form along with vapor condensates. Over time these become available in sufficient quantities in matrix material to support growth of microorganisms. This study describes and characterizes some of the chemistry of steam vent habitats, the means developed to sample steam and steam deposits aseptically, using a steam condenser and a simple sample collection device. We describe and evaluate controls producing contamination-free steam and steam deposit samples for analysis. The chemistry of different types of vents studied so far includes nonsulfur, sulfur and iron. Recent iron vent and salt cave studies will be considered. These steam bathed sites harbor both known and unknown organisms, typically but not exclusively, Archaea, that have been grown or are present in quantities sufficient to identify by cloning, and then isolate and describe some of their physical features as well as the means used for enrichment and isolation. We report two recent new isolates from an extreme non-sulfur cave and an iron vent (~pH 3; 85.5 °C) and describe revised equipment used to capture steam samples from low pH high-temperature cave/vent habitats. Overall, we report on steam cave/vent habitats, sampling, enrichment, isolation and identification, as well as structural features of isolated organisms found at low pH and near maximum temperatures for these high-altitude geothermal habitats. Our understanding of the features of life in one of the most extreme and abundant habitats that provide the limits of existence will help produce a model for life beyond Earth’s extreme boundaries.

Keywords: Acid, Archaea, fumarole, iron, nonsulfur, salt, sulfur, thermophile