A master switch allows bacteria, already living in extreme environments, to survive times of crisis
Japanese researchers have identified a molecular mechanism by which bacteria found in hot springs can survive hard times. Interestingly, about half the genes involved are similar to those found in humans, but the key regulator gene is not.
The researchers—all associated with RIKEN’s Harima Institute and the SPring-8 synchrotron—form one of three teams involved in a major project to document the molecular processes of the HB8 strain of Thermus thermophilus, an extremophile bacterium that occurs naturally at temperatures of up to 85 ˚C (Fig. 1). This bacterium was selected because it is relatively simple, built around 2,200 genes, about half the number of the model bacterium, Escherichia coli. The research team is particularly interested in the regulation of transcription, whereby DNA is translated into functional proteins.
In order to survive, organisms have to respond to changes in environmental conditions. At times of nutrient depletion, for instance, bacterial metabolism switches from activities to do with growth and replication to those concerned with adaptation and survival. This involves decreasing the activity of one set of genes and increasing the activity of another, and is often regulated by transcription factors. One group of proteins known to be involved is from the cyclic AMP receptor protein/fumarate and nitrate reduction regulator (CRP/FNR) family, of which there are four representatives in T. thermophilus.
The researchers investigated one of these regulators which they named stationary phase-dependent regulatory protein (SdrP), because they found its activity increased at times of nutrient depletion when the bacterium entered what is known as the stationary phase. They published details of their work recently in Molecular Microbiology (1).
Using an sdrP-deficient strain, they found the gene was non-essential, although the strain showed growth defects and increased sensitivity to certain chemical stresses. Loss of functional SdrP was manifested in decreased activity of eight dependent gene promoters. Based on the amino acid sequences and three dimensional structures of the protein products of the genes regulated by these promoters, the researchers speculate they are involved in activities such as securing nutrient and energy supply, and protecting against oxidation damage to DNA—in short, preparing the bacterium to survive times of crisis.
The researchers are continuing their work to understand the essential transcription mechanism of T. thermophilus, a bacterium thought to be close to early life forms. “We hope this research will help us understand more complicated biological phenomena, including those of human cells,” says team leader, Akeo Shinkai of the RIKEN SPring-8 Center.
1. Agari, Y., Kashihara, A., Yokoyama, S., Kuramitsu, S. & Shinkai, A. Global gene expression mediated by Thermus thermophilus SdrP, a CPR/FNR family transcriptional regulator. Molecular Microbiology 70, 60–75 (2008).