ORIGIN AND GEOMICROBIOLOGY OF MAZE-LIKE CAVE WALL FORMATIONS

Enigmatic, maze-like wall formations called vermiculations are found in caves throughout the world. Previous research on vermiculations found in the sulfidic zone of the Frasassi cave system (Italy) showed that they host an unexpectedly diverse microbial community including autotrophs, and have organic carbon contents between 5-25% by mass¹. However, the origin of vermiculations remains controversial, and the geomicrobiology of the formations is poorly studied. Here we present the most comprehensive survey of vermiculation microbial communities available to date, including actively forming and fossil vermiculations. We also compare the geomicrobiology and geochemistry of vermiculations growing in close proximity to either organic (bat guano) or inorganic chemical (sulfide) energy sources. The results of a long-term manipulation experiment show that actively growing vermiculations regenerate more quickly in zones where a higher chemical energy flux is available for biological activity. Stable carbon and nitrogen isotope data and relationships between the vermiculations and minerals on the cave walls strongly suggest an important role for microbial activity in forming and stabilizing the vermiculations on timescales of 100,000 to 200,000 years. Our data also show that vermiculations are a rich reservoir of subsurface microbial life with the potential to shed new light on future biogeographical, drug discovery, and metabolic diversity investigations.

[1] Jones et al (2008), Journal of Cave and Karst Studies 70, 78-93