Genetics of pressure-sensing and adaptation in a deep-sea bacterium

Doug Bartlett, Ph.D.
Scripps Institution of Oceanography
University of California, San Diego

Friday, October 16, 1998
12:00 Noon—Pacific Forum

Piezophiles (also referred to as barophiles) are micro-organisms whose optimal pressure for growth and reproduction are above one 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 psychrotolerant, moderately piezophilic deep-sea 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. Piezoregulation of the omp gene 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 synthesis will be described.

Finally, additional genetic experiments which have led to the identification of a DNA recombination protein which also greatly influences cell growth at high pressure will be presented.

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