Ecology of Two Terrestrial Serpentinizing Fluid Seeps Offers a Glimpse of the Deep Biosphere
Abstract
Terrestrial serpentinizing fluid seeps provide convenient access to the deep subsurface biosphere community. Serpentinization--the hydrous alteration of ultramafics--produces hydrogen and possibly methane gas. Chemotrophic microbes utilize these compounds, and may form the base of the deep subsurface trophic web. Here, the geochemical environment of two terrestrial serpentinizing fluid seeps was characterized and community composition was determined. The first site is Yanartas in the Tekirova ophiolite complex (Turkey). Yanartas hosts gas and fluid seeps, the latter of which may be ephemeral. The second site is Manleluag Spring in the Zambales ophiolite range (the Philippines). In Manleluag, the fluid seeps result in the formation of large carbonate terraces. Illumina MiSeq sequencing of the small-subunit rDNA (universal primers) from Yanartas and Manleluag indicates distinct microbial communities, with some shared taxa. Methanogenic archaeal taxa were present in sediments collected from both seeps. The most dominant taxa were the Methanobacteria, with Manleluag sediments having a ten-fold higher abundance than Yanartas. The nitrifying archaea, Thaumarchaeota, were also found at both sites. Bacterial populations at both locations are diverse and primarily composed of heterotrophic taxa. At Yanartas, Alpha- and Betaproteobacteria taxa are dominant (~60% total), while at Manleluag these taxa are only 10-20% of the total reads. Clostridia and Bacteriodetes comprise nearly 35% of the sequence data at the source seep in Manleluag; at Yanartas these taxa make up ~10% of sequence data. Down an outflow channel at Manleluag, the population shifted to Thermales and Hydrogenophilales (~50% of sequence data). At Yanartas Alpha- and Betaproteobacterial taxa continued to dominate downstream, but in one outflow channel an orange, mineralized biofilm is evident. This pigmentation may result from the carotenoid-producing Rhodobacteraceae, which were only found in the orange biofilms. Despite the variations in taxonomic diversity at both sites, functional diversity inferred from sequencing data is similar. The presence of Thaumarchaeota taxa at both locations suggests ammonia oxidation. Methanogenic archaeal taxa may indicate methanogenesis, but it is possible that these archaea are using methanogenesis pathways in reverse (methanotrophy). Clostridia and Bacteriodetes were present at both seep sources, which suggests anaerobic fermentation is a viable metabolism. The ability of Clostridia to form spores may be advantageous at the ephemeral Yanartas seep. The contrast between anaerobic taxa abundances at both locations may be due to the difference in surface mixing at the seeps' surface expressions. Sequencing reads from both localities revealed a preponderance of methanogens, fermenters, and nitrifiers that may be remnants of a deep subsurface population exposed abruptly to atmospheric conditions. Further work is necessary to determine which metabolisms are most active within the microbial community, and to ascertain the biogenecity of the methane at both seeps.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.B13C0510W
- Keywords:
-
- 0465 BIOGEOSCIENCES Microbiology: ecology;
- physiology and genomics