N-137. Characterization of Microbial Communities in Biofilms Associated with Rock Varnish from Panamint Valley, CA

E. M. Eggleston1, W. D. Leavitt2, J. M. Tor1;
1Hampshire Coll., Amherst, MA, 2Harvard Univ., Cambridge , MA.

Rock varnish is a dark, thin, layered veneer composed of clay minerals cemented together by oxides and hydroxides of manganese and iron. Despite decades of study, the nucleation and growth mechanisms of rock varnish remain a mystery. Microbial Mn(II) and Fe(II) oxidation could result in the formation of metal oxides as mineral phases in varnishes, as occurs in other environments. The purpose of this research was to characterize microbial communities associated with rock varnish and identify those microorganisms able to precipitate Mn- and Fe-oxides. Rocks coated in varnish were collected from the Panamint Valley region of Death Valley National Park. They were placed in a flow-through biofilm chamber and a minimal growth media containing dissolved Mn- and Fe-oxides was dripped over the rocks at a constant rate. DNA was extracted from native rock varnish and from biofilms displaying evidence of metal precipitation after 3 months of continuous growth. The 16S rDNA genes were amplified by PCR, analyzed via DGGE, and sequenced. The microbial community present in the rock varnish biofilm contains many previously undescribed and uncultured bacteria as well as new species in known genera (e.g. Micromonospora sp.), some of which have previously been described in rock varnish, while others are novel and may result from the unique use of the biofilm flow-through apparatus. The identification of the microorganisms present in the rock varnish biofilm will aid in elucidation of the role that microorganisms play in the accumulation of Mn- and Fe-oxides and the biogenicity of rock varnish formation.