Abstract:
Su lfid ic cave walls host abundant, rapid ly-growing micro bia l communities that display a variety o f mo rphologies previously described for verrn iculations. Here we present molecular, microscopic, isotopic, and geochemical data describing the geomicrobiology o f these biovennic ulations from the Frasassi cave system, Italy. The biove rm iculations are compo sed of densely packed prokaryo tic and funga l cells in a mineral-organ ic matrix co ntaining 5 to 25% o rganic carbon. The carbon and nitrogen isoto pe compositions o f the biovermiculations (ti 13e = - 35 to - 43%0, and til 5N = 4 to - 270/00. respectively) indicate that with in sulfidic zo nes, the o rga nic matter o rigina tes from chemolithotrophic bacterial primary productivity. Based on 165 rRNA gene cloning (n=67). the bioverrn ... iculation communitv is extrernelv diverse, incl uding 48 . ~ . ... representative phylotypes (>98% identity) from at least 15 major bacterial lineages. Important lineages include the Betaproteobacteria (1 9.5% of clones). Gammaproteobacteria (1 8%). Acidobacteria (1 0.5%). Nitrospirae (7.5%). and Planctomyces (7.5%). The most abundant phylotype, comprising over 100/0 of the 16S rRNA gene sequences. groups in an unnamed clade within the Gammaproteobacteria. Based on phylogenetic analysis, we have identified potential sulfur- and nitrite-oxidizing bacte ria. as well as both auto- and heterotrophic members of the biovermiculation community. Additionally. many of the clones a re representatives of deeply branching bacterial lineages with no cultivated representatives. The geochemistry and microbial composition of the biovermicula tions suggest that they play a role in acid production and carbonate disso lution. thereby contributing to cave formation.