Calcium carbonate of microbial origin in the Etruscan tombs of Tarquinia.

The UNESCO World Heritage Etruscan necropolis of Tarquinia, (Viterbo, Italy), is the site of more than 200 painted hypogeal tombs (dated from the 7th to the 2nd century B.C.). In the Etruscan hypogeal tombs, we previously identified the presence of a thick secondary calcium carbonate nanocrystals deposit of biogenic origin (the moonmilk), usually found in karstic caves. The analysis of the bacterial communities of these deposits revealed that the rocks where the Etruscan hypogea were carved, the macco, contained the microbial community responsible for moonmilk formation. These communities harbor mainly mesophilic (non-extreme) bacteria, but cyanobacteria, such as the genus Chroococcidiopsis was found in abundance in the Tomba delle Sculture and Tomba Bartoccini that are kept in the dark. The moonmilk also hosts many bacterial species able to produce calcium carbonate in laboratory conditions. The study of the interactions between microbes and rock (e.g. moonmilk formation) and biomineralization can provide information with potential value for life detection.