Genetic Analyses of Piezo-sensing and Piezo-adaptation in Photobacterium profundum SS9
Douglas H. BARTLETT*, Eric E. ALLEN, Kelly A. BIDLE, Lakshmi N. CHILUKURI and Tetsushi KOMATSU
Center of Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California. San Diego. La Jolla. California. U.S.A. 92093-0202
Piezophiles (also refered to as barophiles) are microoorganisms whose optimal pressure for growth and reproduction are above 1 atmosphere. Unlike many extremophiles, most cultured piezophiles are closely related to well studied marine bacteria, a fact which has helped make it possible to apply genetic tools to the study of one of their members.
The psychrotrophic, moderately piezophilic bacterium Photobacterium profundum SS9 has been the subject of genetic manipulation of processes associated with both pressure-sensing and high-pressure and/or low-temperature adaptation. SS9 responds to changes in pressure by a) inversely altering the expression of two outer membrane protein encoding genes and b) by changing its fatty acid composition. omp gene piezoregulation depends on the activity of a membrane localized protein bearing homology to the ToxR family of transcription factors. Pressure/temperature effects on SS9 ToxR abundance and activity help explain the function of this protein in piezoregulation. The results of experiments using membrane-perturbing local anesthetics are consistent with a role for changes in membrane structure (fluidity) in ToxR-dependent piezosignaling. Membrane structure is also critical to piezoadaptation. The characteristics of piezosensitive mutants impaired in mono- or poly-unsaturated fatty acid production as well as mutants exhibiting increased piezophily will be described.
Finally, experiments comparing the effects of high pressure on protein-protein stability using a model protein (single-stranded DNA binding protein) obtained from related bacteria differing in piezo-adaptation will be presented.
1. Bartlett, D.H. and Bidle, K.A. (1998) Membrane-based adaptations of deep-sea piezophiles, In J. Seckbach (ed.) Origin-evolution and versatility of microorganisms, Kluwer Publishing, Amsterdam, in press.
2. Kato, C., and Bartlett, D.H. (1997) The molecular biology of barophilic bacteria. Extremophiles, 1, 111-116.
3. Bartlett, D.H., Kato, C. and Horikoshi, K. (1995) High pressure influences on gene and protein expression. Res. Microbiol., 146, 697-706.
