ALL THAT GLITTERS IS NOT GOLD: MICROBIAL COMMUNITIES THAT MASQUERADE AS MINERAL DEPOSITS

Lava tubes (pyroducts) contain a wealth of colorful microbial mats, but in addition to these clearly biological deposits, there are many non-biological appearing mineral deposits. These deposits include an amorphous copper-silicate deposit (Hawaii), which is blue-green in color, resembling chrysocolla, which contains many biological morphologies. In the Azores, lava tubes contain iron-oxide formations, a soft ooze-like coating, and pink hexagons, while gold-colored veins and shredded gold-colored deposits are found in lava tubes in New Mexico and Hawaii respectively.

A combination of scanning electron microscopy (SEM), culture-independent molecular techniques, and culturing studies has revealed diverse microbial communities that inhabit these mineral-like deposits. Samples of these deposits were collected aseptically and either mounted directly on SEM stubs, covered with sucrose lysis buffer to break open cells and stabilize the DNA, or introduced into growth and selective isolation media. DNA was extracted from the buffered samples, amplified with universal bacterial primers, cleaned, cloned, sequenced, and analyzed phylogenetically. Cultures were transported to the laboratory for long-term incubation in the dark at temperatures that approximate cave temperatures. SEM revealed a variety of biological morphologies, including reticulated filaments in the blue-green deposits, bumpy filaments in the gold veins, and iron-oxide coated filaments in the pink hexagons. Molecular analysis revealed the presence of nine phyla across these deposits, including Proteobacteria, Acidobacteria, Gemmatimonadetes, Verrucomicrobia, Bacteroidetes, Planctomycetes, Firmicutes, Acidobacteria, TM7, and Nitrospirae. Cultures are producing several biological pigments and iron, copper, and manganese minerals in the media. Unlike the microbial mats, no Actinobacteria were found in these deposits. Investigation of such deposits that are not obviously biological, allows us to enhance our ability to detect biosignatures of their presence with applications to the analysis of potential biotextures in the rock record of Earth and the search for microbial life on other planets. Additionally, it expands our knowledge of the diversity and microbe-mineral interactions specifically in lava tubes.