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Grogan, Dennis W.

Dr. Dennis W. Grogan

Associate Professor
Department of Biological Sciences
University of Cincinnati
Cincinnati, OH




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.