Extremophiles in the Evolution of Life

A focus of research on extremophiles has centered on the hyperthermophiles. As discussed earlier, there is good reason to believe that at least some hyperthermophiles have evolved relatively little from their ancestors present on earth over 3.5 billion years ago. If true, an understanding of the biology of hyperthermophiles may yield a glimpse of what life was like eons ago. In this connection the genomes of several hyperthermophiles have been sequenced and the large number of genes they contain that lack counterparts in other organisms suggests that their biological secrets have at this point only been partially revealed. As if living in boiling water isn't enough, just imagine what other tricks hyperthermophiles might be able to perform!

As previously mentioned, the excitement in microbial diversity these days comes from the fact that the evolutionary history of the prokaryotes can now be experimentally determined. Microbiologists no longer have to propose bacterial phylogenies based on speculation or "educated guesses" of what type of microbe likely preceded another; the phylogenies themselves are etched in the sequences of molecules and all one has to do is read them (figure 30e.7). Moreover, the application of molecular phylogenetic methods to natural environments has given us the exciting news that the diversity of the microbial world is enormous-indeed it is beyond our wildest expectations. Thus, in the final analysis bacterial diversity will likely dwarf that of all of the rest of biology, perhaps by several orders of magnitude. But only continued and expanded research into the diversity of microbial life in all environments, extreme and otherwise, will yield the data needed to confirm this.

FIGURE 30e.7
A tree of life. A phylogenetic tree of life based on comparative small subunit ribosomal RNA sequences. Note the three domains of life, two of which are prokaryotic.

It may indeed be humbling to many biologists to think that prokaryotes dominate living diversity. But within the rich genetic resources of the prokaryotes undoubtedly lies more benefit for humankind than we will extract from any other group of organisms. Antibiotics, fermentation, and biotechnology are only the beginning. The best is yet to come.

Due to their diversity and genetic uniqueness, extremophiles and bacteria in general may hold many secrets that are of evolutionary and practical significance.