MICRO-ORGANISMS FROM EXTREME
ENVIRONMENTS
MOLECULAR BIOLOGY OF
HYPERTHERMOPHILES
GENETICS OF ARCHAEA
Much of the biochemical diversity of life on
earth is embodied in single-celled organisms. The smallest and most widely
distributed of these are the prokaryotes, whose cells lack nuclei and other
membranous organelles. The best-known group of prokaryotes, the bacteria,
include a few species that cause disease, and many others that mediate
geochemical cycling, degrade toxic pollutants, or produce antibiotics or other
useful products. About 25 years ago, Carl Woese at the
University of Illinois discovered a second, evolutionarily distinct, group of
prokaryotes through analysis of ribosomal RNA sequences. Much less is
known about this second group, called "Archaea".
Many of the archaea that have been successfully grown in pure culture come from
hostile or otherwise unusual environments, yet they show certain similarities to
eukaryotic cells at the molecular level.
My students and I focus on thermoacidophilic
archaea of the genus Sulfolobus. These species normally live in acidic hot springs,
and their optimal growth conditions (80ยบ C and pH 3) quickly inactivate the DNA, RNA,
enzymes, and membranes of "ordinary" cells. We want to understand in
molecular terms how the Sulfolobus cell functions under these harsh conditions.
Like other hyperthermophiles, Sulfolobus
spp. have thermostable enzymes that
exhibit maximal activity at extremely high temperatures. Like other
archaea, their cells have an unusual cell envelope composed of ether-linked isoprenoid
lipids and a flexible layer of glycoprotein subunits. These features, though
unusual, seem very effective for preserving cellular integrity at high temperature and
low external pH. Intracellular processes, such as DNA metabolism, are also
expected to have molecular adaptations for life under these conditions, but
these phenomena are more
difficult to observe and manipulate experimentally.
To address this challenge, research in the Grogan
lab emphasizes development of basic genetic techniques that allow specific
molecular processes to be analyzed in vivo under extreme conditions.
We
have isolated various mutant strains of S. acidocaldarius and used them
to investigate archaeal cell division,
responses to DNA damage, transfer and recombination of
chromosomal DNA, and fidelity of genome
replication. We have also conducted detailed analyses of homologous
recombination, deletion formation, and the properties of insertion sequences in Sulfolobus,
and have helped collaborators
at UC-Berkeley evaluate the genetic isolation of natural Sulfolobus
populations around the world.
We expect future progress on these and related questions to be
greatly helped by the availability of genomic
sequences and DNA micro-arrays of S. acidocaldarius and other
species.