MICROBIAL COMMUNITY AND FUNCTIONAL DIVERSITY IN A BASALTIC LAVA CAVE BIOFILM

Cooled lava provides a sterile habitat with plentiful nutrients for life to colonize, but these nutrients are initially difficult to access for most organisms. Weathering processes facilitate access to nutrients through geochemical, physical, and biological agents. Biofilms colonize bare lava rock and are known to secrete organic acids to increase mineral leaching and bioavailability, but biological weathering's significance as a weathering mechanism is difficult to disentangle from abiotic weathering processes [1]. To examine microbial contributions to weathering, we studied biofilm communities in lava caves with minimal abiotic influences. Lava Beds National Monument (LBNM) is located in a high desert environment with Holocene and late Pleistocene-age basaltic lava caves. The walls at the entrances of lava caves host microbially dominated ecosystems where wind- and water-driven weathering is limited, allowing for greater isolation of biological weathering effects. We sampled three caves from lava flows of two different ages. In each cave, we identified three microbial communities by color—pink, light green, and dark green. Each sample included microbial biofilm, the rock immediately below the biofilm, and the underlying unweathered rock. We assembled a metagenome from the pink biofilm community of Sunshine Cave (36 ka) within LBNM. Preliminary metagenomic analysis indicates the presence of a radiation-resistance gene as well as genes associated with weathering processes. Future work will combine microbiological community surveys with geochemical analysis, via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), to analyze how host rock geochemistry varies spatially with relation to the surface biofilm.

References:

[1] Tourney J. & Ngwenya B.T. (2014) Chem. Geol. 386, 115-132.