Microbes in caves: agents of calcite corrosion and precipitation - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 12

Fig. 4. SEM photomicrographs of Geitleria calcarea from walls of a poorly illuminated cavity in a limestone
breccia that fills a sinkhole in the Bluff Formation, southeast Grand Cayman. (a) Individual specimen resting on biofilm
that is formed of mucus and filamentous microbes. (b) Longitudinal section showing hollow core and wall of the
filamentous microbes encrusted with dendritic calcite crystals. (c) Open lumen with encrusting dendritic calcite crystals.
(d) Encrusting dendritic calcite crystals encasing filament. Black background introduced, using Photoshop #,in
order to highlight encrusting crystals. (e) Exterior of microbe showing dendritic calcite crystals. (f ) Enlarged view of
dendritic calcite crystals.

(Fig. 4). Being from the interior, poorly illuminated
areas of the cavities, they are equivalent to forms
found in the twilight zones of caves. The dendrite
crystals, characterized by primary, secondary, and
tertiary levels of branching form intricate crystal
networks that completely envelope the micro-
bes (Fig. 4e,

characterized by different crystal architectures.
Some of the filamentous microbes on the cave
walls in the twilight zone of the Old Man Village
cave, for example, are encrusted with very small
crystals that are difficult to characterize even at
high magnifications on the SEM (Fig. 5). These
crystals appear to be small prismatic forms that f ). Other calcified microbes are