Black Mats

A mix of microbial biofilms in Upper Spring, in which the black mat is the focus of this section. Rocks in the foreground are approximately 20 cm across. White patches in the black and red areas are also microbial mat of filamentous sulfur bacteria, similar to other places in the cave. 

The SEM images below show interesting framboid structures associated with the microorganisms found in the mats. Elemental analysis of the crystals reveals that the major composition is Fe and S. So far, we have identified a mix of aerobic and anaerobic heterotrophs, or possibly chemoorganotrophs. Preliminary evidence suggests that iron-reducers and methanogens are also present. 

Scanning Electron Microscopy of Microbial Mat and Sediments:

Microbial biofilms and sediments were preserved in gluteraldehyde, then freeze-dried. Prepared samples were gold-coated and observed using the JEOL SEM in the department. The images were digitally captures and the size was adjusted to fit on the web-page, causing some distortion. 
Two types of Fe-S framboids, one of solid crystals (like a popcorn ball) and another comprised of separate crystals contained in a biofilm or membranous sac. Cells range in size from 2 mm to < 1mm. Filamentous cells or fungal hyphae were also observed.  An exploded crystal sac near a thick organic biofilm (notice layered cells on upper left side of image). 
Another type of framboid, showing dented crystal faces, also associated with organic material.   Close-up of above image, in which it is obvious that the small objects are tiny crystals, having differing number of crystal faces.   

  Last updated:  07/13/09   Images, maps, and other original material copyrighted by Annette Summers Engel, Baton Rouge, LA, USA.