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Project Progress

Diversity of Eukaryotes in Thermophilic and Mesophilic Environments that might Resemble Early Earth’s Biosphere (dm)

Molecular microbial ecology studies have revealed remarkable prokaryotic diversity in extreme hydrothermal marine environments. There are no comparable reports of culture-independent surveys of eukaryotic life in warm, anoxic marine sediments. Using sequence comparisons of PCR-amplified small subunit ribosomal RNAs, we characterized eukaryotic diversity in hydrothermal vent environments of Guaymas Basin in the Gulf of California. These anoxic sediments and the overlying seawater harbor a mixture of genetically diverse protists. Many sequence isolates represent novel protists, including early branching eukaryotic lineages or extended diversity within described taxa. At least two mechanisms, with overlapping consequences, account for the eukaryotic community structure of this environment. The adaptation to warm anoxic environments is evidenced by specific affinity of environmental sequences to microaerophilic species in molecular trees. This is superimposed on a background of widely distributed aerophilic protists, some of which may migrate into and survive in the sediment while others, e.g. phototrophs, are simply deposited by sedimentary processes. This year we completed the phylogenetic analysis of eukaryotic 18S rrNA sequences from the upper 3 cm layers of two Guaymas Basin cores.