Research Overview

            Phylogenetic studies divide prokaryotes into bacteria and archaea (embed image: phylo tree.jpg). Hyperthermophiles are present in both groups and since their rDNA is unusually deeply rooted they appear to have arisen early in history. Though archaea are phylogenetically distinct from eukaryotes, there is remarkable conservation between their general transcription components including RNA polymerase, promoters and general ranscription proteins. While “basal” transcription is conserved, the regulation of transcription initiation by regulatory proteins remains largely undefined. The major focus of my laboratory is to better understand archaeal gene regulation. We use the hyperthermophilic microbe, Sulfolobus solfataricus (LINK to image: single Sso cell.jpg), as a model organism.

Focus 1: Archaeal Catabolite Repression

            S. solfataricus, is the best characterized member of the Crenarchaeotal subdivision of the archaea. We culture it aerobically at 80°C (176°F) and at a pH of 3. Some years ago, we discovered a Catabolite Repression (CR) response in this organism operating at the transcriptional level at loci encoding glycosyl hydrolases. Using a genetic approach we identified a trans-acting regulatory factor called CAR that mediates regulation of gene expression at the level of transcription initiation (and not degradation). Recent studies using DNA arrays and proteomics indicate CAR is a global regulator of gene expression. These studies will clarify further the evolutionary position of these organisms and will identify the mechanisms which have evolved to overcome the inherent biophysical constraints imposed on the regulation of their gene expression at temperature extremes.

Focus 2: Mercury Resistance and Toxicity in Archaea

            Mercury is an historic antimicrobial and toxic heavy metal (embed image: cinnabar.emf). Many Archaea thrive in metal rich environments but little information is available about the biology of heavy metals and these organisms. To investigate this question studies mercury resistant archaea were cultured from a cinnabar hot springs (pH 1.7, 78 °C, 2 mg/liter mercury) located in the Mojave Desert (embed image: MVC-0019.JPG) . Recent molecular genetic studies identified presence of an enzymatic detoxification system and a novel form of gene regulation that overcomes the effect of mercury as a transcriptional posion. To get at the question of the origin of these resistance genes and their potential lateral gene transfer the microbial biodiversity of the mercury geothermal pool has been examined using culture-independent and culture-based methods. This information will extend knowledge about life in extremely oxidizing environments and contribute to the genetic manipulation of archaeal hyperthermophiles.

Focus 3: Functional Genomics and Proteomics of S. solfataricus

            The genome of Sulfolobus solfataricus is completely sequenced (link to: http://www-archbac.u-psud.fr/projects/sulfolobus/). Together with our methods for targeted disruption, we use functional genomics to investigate the biology of this organism. This has led to an expanding roster of collaborative proejcts with Sulfolobus labs around the world.