FIGURE 3.

Examples of the unsaturated or vadose zone in limestone caves from Lazio region, Italy. Water is transferred in the deep zone of the cave across vertical wells (A–B). Biofilms colonize the walls near the cave entrance and appear overlaid by water droplets reflecting gold- or silver-colored light when illuminated with an LED lamp (C). Close-up image (D) showing yellow microbial communities organized into similarly sized spheroidal structures (about 60 µm in diameter) retaining water droplets due to the condensation of the water vapor. Scale bar (C, 100 µm). Photo by P. Turrini.