Bacterial Associations with Weathering Minerals at the Regolith-Bedrock Interface, Luquillo Experimental Forest, Puerto Rico

Microbe-mineral associations in regolith overlying granodiorite bedrock (4.6-4.9 m depth) from the Luquillo Experimental Forest, Puerto Rico, were imaged with confocal scanning laser microscopy at a novel scale of 400X magnification. After adding BacLight (TM) stain, proportionally more surface area of minerals (quartz, biotite, and mixed opaque kaolinite/goethite) emitted fluorescence from cell-impermeant propidium iodide than from cell-permeant SYTO 9, which suggested greater coverage of minerals by extracellular DNA or DNA in non-intact cells than by intact cells. Microscopic observations of predominantly non-intact cell material in deep saprolite were consistent with the abundance of rRNA sequences related to heterotrophic bacteria in clone libraries prepared from community DNA. A few sequences were affiliated with bacteria recognized to produce siderophores, oxidize Fe(II), or fix N-2. Bacterial DNA in deep regolith from two boreholes 1.5 m apart yielded libraries with high diversity and taxa specific for each borehole. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.