N-154. Microbial Community Composition and Diversity in Unusual, Ophiolite-Hosted Alkaline Waters

S. J. Green1,2,3, D. F. Blake2, J. G. Blank1;
1SETI Inst., Mountain View, CA, 2NASA-Ames Res. Ctr., Moffett Field, CA, 3Florida State Univ., Tallahassee, FL.

We characterized microbial community composition and diversity associated with waters in the vicinity of Adobe Springs, in the Del Puerto Ophiolite (Coast Range, CA). The moderate alkalinity (pH 8.5-9) we measured most likely reflects a mixture of meteoric water and high-pH water derived from the alteration of Fe- and Mg-rich ultramafic rocks within the ophiolite. We identified three "ecozones" in our field area: (1) anaerobic groundwater from the untreated, Adobe Springs well, (2) aerobic surface water from the creek and primary drainage in the area, and (3) a small, artificial pond fed by well water. We collected water samples for chemical analysis of major and trace constituents. We also filtered water to collect biomass from each setting and sampled a microbial mat and underlying sediment from the pond. Extracted genomic DNA was subjected to PCR amplification using primers targeting rRNA genes of bacteria, archaea, and a methanogen-specific functional gene, mcrA. Bacterial sequence analyses revealed substantial differences between the communities sampled; the groundwater had high diversity while the creekwater was dominated by a single alkaliphilic Bacteroidetes. The mat was populated by two novel clades of Cyanobacteria closely related to organisms found associated with geothermal microbial mats. Archaeal communities included methanogenic archaea in the groundwater, microbial mat, and sediment, as well a cluster of putatively heterotrophic Archaea in all samples. H2-consuming methanogens, closely related to Methanobacterium alcaliphilum, were abundant in the mat. Further analysis of the methanogens employing mcrA genes exposed a more diverse methanogen community in the groundwater and some overlap with the sediment methanogens. In general, the bacterial communities differed largely between sampling locales whereas the non-methanogenic Archaeal communities were relatively similar. These data imply selective pressure from the unique water chemistry and complex relations between the water chemistry, environmental factors, and the subsurface microbial community.