2000 Annual Science Report
Marine Biological Laboratory Reporting | JUL 1999 – JUN 2000
Diversity of Eukaryotes in Thermophilic and Mesophilic Environments That Might Resemble Early Earth's Biosphere
Environmental conditions in anaerobic marine sediments may closely resemble those under which eukaryotes diverged from a prokaryote precursor 2-3 billion years ago. Yet little is known about eukaryotic microbial populations in these environments, leaving a substantial gap in our understanding of vent biota. We have initiated a study of eukaryotic microbial community composition based upon SSU rDNA sequence analyses of sediments from Guaymas Basin (Gulf of California). Temperature profiles were measured concurrently at 5-cm depth intervals, and the cores were sectioned anaerobically into 1-cm segments. We used eukaryotic-specific primers to PCR amplify rDNA genes. Sequence of the amplified products were merged with a large data base of eukaryotic ribosomal RNAs and subjected to phylogenetic analyses.
PCR amplifications were achieved for samples from 0-3 cm (60°C) depth in core A and 0-3 cm (40°C) plus a seawater interface sample from core C. We have sequenced ~45 clones from each of the 1-cm horizons from both cores. Phylogenetic analysis of horizons 0-1 from core C and 0-1 and 1-2 from core A reveal a broad array of eukaryote taxa. Many sequences cluster among known taxa: metazoa, green plants, dinoflagellates, apicomplexa, ciliates, stramenopiles (e.g., diatoms), and fungi. Several sequences could not be assigned to any known eukaryotic phyla. Several closely related clones from the 0-1 and 2-3 cm horizons from core C branch deep within the eukaryote lineage between the parabasalids and the eukaryotic crown taxa. Of particular interest among the cloned rDNAs is the deep-branching clone C1_E027. Its position between described anaerobic, early eukaryotes is evidence of a primitive, previously non-described organism. Although this sequence was obtained from a relatively cool (3-25° C) sediment sample, the spatially and thermally dynamic nature of hydrothermal vents imply that the organism might reside at even higher temperatures. We have already demonstrated a remarkable diversity of eukaryote rDNAs in hydrothermal vent sediments, but we have only scratched the surface of the potential diversity in this environment.
PROJECT MEMBERS:Virginia Edgcomb
Alvin de Vera Gomez
RELATED OBJECTIVES:Objective 4.0
Expand and interpret the genomic database of a select group of key microorganisms in order to reveal the history and dynamics of evolution.
Define how ecophysiological processes structure microbial communities, influence their adaptation and evolution, and affect their detection on other planets.
Identify the environmental limits for life by examining biological adaptations to extremes in environmental conditions.