One of the most productive and exiting aspects of life at extreme environments has been the discovery and description of novel metabolic types of hyperthermophilic archaea and bacteria at deep sea hydrothermal vents. Many of these extremophiles represented new genera (e.g. Pyrodictium, Methanopyrus. Staphylothermus, Archaeoglobus) exhibiting types of metabolism and enzymatic capabilities that were entirely unexpected to occur at high temperatures. A case in point is the recent isolation of Pyrolobus fumarii with its ability to ammonify nitrate and to use thiosulfate as well as oxygen at low levels as electron acceptors. These traits greatly extend the type of microbial transformations that can be projected to occur at high temperatures of oceanic, terrestrial or extraterrestrial environments. There is no reason to assume that this deep sea source of novel extremophiles is exhausted. We will combine new enrichment/isolation approaches for hyperthermophiles with a molecular/phylogenetic assessment of their in situ occurrence. To this end we will use denaturing gradient gel electrophoresis (DGGE) for a visual assessment of microbial biodiversity, rapid identification and parallel studies of molecular and cultured isolates. The field work and sample collecting will be done with the DSRV ALVIN at two most productive and, although in close proximity, characteristically different hydrothermal vent sites: Guaymas Basin and 21 ÃN at the East Pacific Rise. Dilution techniques will be applied to delineate populations densities and habitat ranges in both our cultural and molecular approaches. We will link the biodiversity aspect to quantification of different metabolic types of hyperthermophilic organisms along selected redox and temperature gradients which commonly occur at Guaymas Basin vent sites and offer small scale analogs of two biospheres normally separated by larger distances: (1) the oxic or anoxic parts of the surface and subsurface biosphere, ultimately driven by photosynthesis, and (2) the possibly autonomous anoxic deep subsurface biosphere. Since the latter may hold organisms mediating biogeochemical reactions such as methane and sulfide formation and possibly anaerobic metal oxidations, their potential role in extraterrestrial environments is particularly intriguing.
