ABSTRACT
RESUMEN En el trabajo se estudió un consorcio microbiano metanogénico de una mina de carbón de la cuenca de Bogotá en Colombia. Se establecieron cultivos de enriquecimiento de carbón ex situ para el crecimiento y la producción de gas de novo. El gas biogénico producido por los cultivos se analizó mediante cromatografía de gases con detectores de ionización de llama y conductividad térmica. Los cultivos se utilizaron para aislar estirpes microbianas y para generar bibliotecas del gene 16S rARN empleando de cebadores de bacteria y de arquea. El análisis de cromatografía de gases mostró producción de metano a 37 oC, pero no a 60 oC, donde el CO2 fue el componente principal del gas biogénico. El análisis de la secuencia del gen 16S rARN de estirpes microbianos y de las bibliotecas de clones, estableció que el consorcio microbiano metanogénico estuvo formado por especies de bacterias de los géneros Bacillus y Gracilibacter más la arquea del género Methanothermobacter. El consorcio microbiano metanogénico identificado es potencialmente responsable de la generación de gas biogénico en la mina de carbón La Ciscuda. Los resultados sugirieron que los metanógenos de este consorcio producían metano por vía hidrogenotrófica o de reducción de CO2.
ABSTRACT The work studied the methanogenic microbial consortium in a coal mine from the Bogotá basin in Colombia. Ex situ coal-enrichment cultures were established for in vitro growth and de novo gas production. Biogenic gas produced by cultures was analyzed by gas chromatography using thermal conductivity and flame ionization detectors. Cultures were used to isolate microbial specimens and to generate 16S rRNA gene libraries employing bacterial and archaeal primer sets. The gas chromatographic analysis showed methane production at 37 oC, but not at 60 oC, where CO2 was the major component of the biogenic gas. 16S rRNA gene sequence analysis of microbial isolates and clone libraries established that the methanogenic microbial consortium was formed by bacteria species from Bacillus and Gracilibacter genera plus archaea from the Methanothermobacter genus. This meth-anogenic microbial consortium was potentially responsible for biogenic gas generation in La Ciscuda coal mine. The results suggested that these methanogens produced methane by hydrogenotrophic or CO2 reduction pathways.
ABSTRACT
Rocks, apart from being ancient records that enlighten us about the geological history of our planet, are dynamic repositories that support life forms central to the sustenance of our biosphere. It is the latter that our discussion will be largely focused on. Life associated with rocks has been documented as early as 1914 (Diels 1914), but it was in the 1960s that Friedmann and colleagues, with their extensive studies on rock-dwellers in hot and cold desert habitats, gave shape to this modern branch of geobiology. The presence of microscopic algae and bacteria was first demonstrated within exposed rocks from hot desert environments such as the Negev and the Sinai (Friedmann and Galun 1974) by electron microscopy and laboratory cultivation methods. Subsequent studies in ortho-quartzite rocks from the Dry Valley area of Antarctica also showed morphologically similar algae (related to the genus Gloeocapsa) to be colonizing areas ~1.5 mm wide parallel to and ~2 mm beneath the rock surface (Friedmann and Ocampo 1976). The results from the latter caught the attention of the scientific community as NASA had been testing their Voyager mission probes on the apparently lifeless cold deserts of Antarctica with the aim of studying a habitat analogous to Mars. In 2005, Walker and colleagues, through the use of culture-independent molecular methods, discovered the microbial colonization of rocks from the extremely acidic (pH~1) Yellowstone geothermal environment. By employing universal PCR primers that targeted 16S rRNA genes from all three domains of life, the authors were able to retrieve sequences phylogenetically related to extant red alga (Cyanidium sp.), bacteria (α-, β-, γ-Proteobacteria; Actinobacteria; Bacteroidetes and Firmicutes) and archaea (Euryarchaeota and Crenarchaeota). The astoundingly high diversity of microbial life forms present in such extreme habitats captured the imaginations of geo(micro)biologists, astrobiologists and microbial ecologists alike. Astrobiologists imagined that if rock interiors could support the major fraction of life in the harshest of environments on earth, then the same could be applicable to other planets such as Mars, and they sensed that there was a need to extend the scope of extraterrestrial life detection missions beyond the mere analysis of top soils. Microbial ecologists wondered if rock-associated life was ubiquitous in the biogeosphere, and geo(micro)biologists hypothesized that the rock micro-habitat offered life (a) protection from intense solar radiations, temperature and desiccation and (b) a supply of nutrients, moisture and growth surfaces. Today, with two dedicated international scientific journals – Geobiology and Geomicrobiology Journal and an ever growing number of papers dealing with rock-associated microbes in microbiological research journals, the concept of ‘life in/on the rocks’ has become as hardened as the rock itself. What is apparently lacking, however, is an understanding among the general public that a ‘dumblooking’ average rock in their gardens (on this planet and perhaps in the gardens of intelligent beings on other planets) could be home to a dynamic assortment of interesting yet diverse living organisms of inevitably microbial nature.