Biofilm Central: The Wonderland of Textures and Bacterial and Archaeal Communities in Cueva De Villa Luz

Cueva de Villa Luz, a limestone cave in Tabasco, Mexico, is home to a wide range of biofilms that vary in texture, color, and microbial composition. The biofilms are exposed to episodic and variable inputs of reduced gases, such as hydrogen sulfide. Thick, mucoid biofilms line the necks of springs that emerge below the surface of the stream that runs through the cave. Culture-independent molecular techniques reveal that these biofilms are dominated by Epsilonproteobacteria, Chloroflexi, and methanogens. The Epsilonproteobacteria are >99% similar to other Epsilonproteobacteria from Lower Kane Cave in Wyoming, which allows us to ask questions about whether geography or geochemistry control species diversity in a habitat. Other mucoid biofilms present on the cave walls include snottites (acidic stalactites) that are dominated by Acidithiobacillus thiooxidans, but also have genetic sequences for flagellates, ciliates, and nematodes. In the dark zone of the cave, green biofilms coat the rocks in the streams and provide food for the insect life of the cave. Culturing experiments suggest that these may be green sulfur bacteria. Most of the passages from the entrance zone to the dark zone contain raised lacey networks of biofilms, called biovermiculations. Culture-independent analyses reveal a more diverse community compared to the other biofilms studied. Organisms present include a variety of soil organisms, Actinobacteria, Alcaligenaceae, Acidobacteria, Gemmatimonadetes, Bacillus spp., and sulfur cycle organisms. These communities demonstrate the influence from the surface and from the deeper subsurface springs. The variety and diversity of these biofilms in Cueva de Villa Luz allow us to understand the different roles that these biofilms play in this ecosystem and the microbial interactions with rock surfaces.