New Mexico Geological Society Annual Spring Meeting — Abstracts

The beautiful colors that paint the desert rocks and the karst cave walls are primarily due to the oxidation of iron (Fe²⁺) and manganese (Mn²⁺). On the terrestrial arid landscape, where weathering and sunlight persists, these oxide layers are called desert varnish. In the subsurface cave environment, where weathering and sunlight are limited or nonexistent, they are called ferromanganese deposits (FMD). Though this oxidation process can be attributed to abiotic factors, recent evidence suggests that microbial influences contribute to these formations for purposes of protection and energy production. However, the exact mechanisms by which they perform this simple activity are not completely understood. This research hypothesizes that microbes mediate Fe²⁺ and Mn²⁺ oxidation, thereby contributing to and influencing the delicate ecosystems of both extreme environments. To test this hypothesis, I pose the following questions: 1) Who are the microbes the comprise the desert varnish and cave FMD?; 2) Are there common and/or novel microbial species present?; 3) Are there any Fe²⁺ and Mn²⁺ oxidizers?; and 4) How are the necessary substrates acquired from their environments?

This investigation begins with samples aseptically collected from Socorro, NM and from Spider Cave in Carlsbad, NM. DNA was extracted for the amplification of representative 16S rRNA genes (~569 bp) via the polymerase chain reaction. Denaturing gradient gel electrophoresis (DGGE) assays were run to identify the relative number of microbial species from each community. Banding patterns suggest common microbial members and that dominant species are also present. Selected bands were picked and reamplifed for subsequent nucleic acid sequencing and phylogenetic analyses. NCBI BlastN shows the presence of bacteria whose closest relatives are the Alpha-, Beta-, and Gammaproteobacteria, Cyanobacteria, and Bacteroidetes. Novel species are suggested, including one whose closest relative is found in the marine environment. Scanning electron microscopy (SEM) reveals the presence of bacteria of various sizes, some possessing unique physiological features that indicate direct interactions with their environment. Classic culturing techniques show the presence of oxides, indicating a similar biogenic process found in the natural environment.