Hyperthermophilic organisms

Figure l.l Black smoker, at a depth of 2,500 m on the East Pacific Rise (by courtesy of John Baross, University of Washington). Hyperthermophilic organisms from such sources have been found to contain hydrogenases. 

Standard rRNA molecular phylogeny (Woese, 1987 Barnes et al, 1996 Stetter, 1996 Pace, 1997) implies the antiquity of hyperthermophile organisms. Though there has been much dispute about the rRNA interpretation, there is some consensus that, whether or not it is the very most ancient, life around hot-water vents is certainly of great antiquity. The implication is that by mid-Archean, hyperthermophile habitats around hot vents were populated by microbial mats, and the waters around hot vents were occupied by free-swimming cells. Mesophile prephotosynthetic plankton probably existed in the open seas, and, distal to the thermophile life in the surroundings of vents, the mesophile habitats further from the hot springs were also occupied. 

Fig. 1. Unusual compatible solutes restricted to hyperthermophiles (organisms with optimal growth temperature >80°).

Still, there seems to be something to this surface-to-volume ratio idea, because a number of normally monomeric enzymes oligomerize when they are found in hyperthermophilic organisms. Adenylate kinase from S. acidocaldarius is a trimer, for example, whereas nearly all other adenylate kinases are monomeric. Perhaps the best evidence that this effect may be important comes from an engineered protein, the repressor of primer (ROP). ROP is normally an all helical homod-imeric protein that denatures at 71°. Removal of five amino acids from a surface... 

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