HR: 0830h
AN: B51C-0977    [PDF]
TI: Mineralogical Control on Microbial Diversity in a Weathered Granite?
AU: * Gleeson, D
EM: deirdre.gleeson@ucd.ie
AF: Department of Industrial Microbiology, Ardmore House University College Dublin Belfield, Dublin, 4 Ireland
AU: Clipson, N
EM: nicholas.clipson@ucd.ie
AF: Department of Industrial Microbiology, Ardmore House University College Dublin Belfield, Dublin, 4 Ireland
AU: McDermott, F
EM: frank.mcdermott@ucd.ie
AF: Department of Geology, University College Dublin Belfield, Dublin, 4 Ireland
AB: Mineral transformation reactions and the behaviour of metals in rock and soils are affected not only by physicochemical parameters but also by biological factors, particularly by microbial activity. Microbes inhabit a wide range of niches in surface and subsurface environments, with mineral-microbe interactions being generally poorly understood. The focus of this study is to elucidate the role of microbial activity in the weathering of common silicate minerals in granitic rocks. A site in the Wicklow Mountains (Ireland) has been identified that consists of an outcrop surface of Caledonian (ca. 400 million years old) pegmatitic granite from which large intact crystals of variably weathered muscovite, plagioclase, K-feldspar and quartz were sampled, together with whole-rock granite. Culture-based microbial approaches have been widely used to profile microbial communities, particularly from copiotrophic environments, but it is now well established that for oligotrophic environments such as those that would be expected on weathering faces, perhaps less than 1% of microbial diversity can be profiled by cultural means. A number of culture-independent molecular based approaches have been developed to profile microbial diversity and community structure. These rely on successfully isolating environmental DNA from a given environment, followed by the use of the polymerase chain reaction (PCR) to amplify the typically small quantities of extracted DNA. Amplified DNA can then be analysed using cloning based approaches as well as community fingerprinting systems such as denaturing gradient gel electrophoresis (DGGE), terminal restriction fragment length polymorphism (TRFLP) and ribosomal intergenic spacer analysis (RISA). Community DNA was extracted and the intergenic spacer region (ITS) between small (16S) and large (23S) bacterial subunit rRNA genes was amplified. RISA fragments were then electrophoresed on a non-denaturing polyacrylamide gel. Banding patterns suggest that the bacterial population in whole rock, which contained approximately 30 separated bands (indicative of the number of bacterial ribotypes), is greater than muscovite (20), K-feldspar (15), and plagioclase feldspar (12) with quartz exhibiting the lowest number (6). These bands were excised from the gel for sequencing, allowing identification of the major populations. An automated approach was also used to assess similarity of bacterial communities present on each sample type, and this allowed for a statistical evaluation of bacterial diversity. Petrographic studies were carried out to assess mineral alteration effects. Scanning electron microscopy (SEM) was used to visualise in-situ bacterial cells.
DE: 1045 Low-temperature geochemistry
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1886 Weathering (1625)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting