Stress by aromatic compounds in Sulfolobus solfataricus: detoxification, regulation and biomonitoring

Most of the archaeal microbial cells, the third domain of life, are adapted to grow in extreme environments not only regarding temperature but also pH, ionic strength and the presence of high concentrations of detergents and organic solvents. As all living cells, they possess a wide variety of finely regulated biochemical systems to defend from environmental stress and, in fact, they own in their genomes regulative sequences responsive to different stress agents (1). Generally, the response can be initiated by binding of transcription factors to particular ligands, such as environmental signals. The thermophilic archaeon S. solfataricus responds to stress by aromatic compounds increasing the expression of a MarR-like operon and of an alcohol dehydrogenase gene (Sso2536adh) (2). The system involves the MarR family transcription factor BldR, which binds to its own promoter inducing auto-activation and increasing the coexpressed drug export permease level. BldR also binds to the Sso2536 promoter stimulating the gene transcription, the accumulation of the ADH enzyme, and hence the enzyme-catalyzed conversion of the aldehydes to the less toxic alcohols (3). A homologue of Bldr, Bldr2, has been recently characterised. DNA binding assays demonstrated that this protein is indeed a transcription factor. Biochemical characterization, as well as transcriptional analyses, suggested that Bldr2 could be also involved in the detoxification/catabolism of aromatic aldehydes. Knowledge of the molecular mechanisms underlying this stress response has revealed crucial to set up a microbial sensing device for the measurement of water-dissolved aromatic aldehydes. The biosensor is an E coli strain expressing the GFP under the control of the responsive Sso2536 promoter, and the gene for the sensor protein BldR.