Isolation of a gene regulated by hydrostatic pressure in a deep-sea bacterium

Abstract

Barophilic bacteria inhabit the deep oceans, and the specific functional modifications and regulatory mechanisms which govern adaptation to hydrostatic pressure are beginning to be understood. For example, the rate of production of several proteins by some hydrothermal vent archaebacteria and the degree of saturation of membrane lipids in other deep-sea bacteria have been found to change as a result of cultivation at high pressure. We report here the cloning of gene, ompH, which encodes a major pressure-inducible protein of strain SS9, a gram-negative eubacterium isolated from a depth of 2.5 kilometres in the Sulu Sea. Messenger RNA encoded by ompH is expressed when cells are grown at 280 atm but not at 1 atm, indicating that transcription of the ompH gene is controlled by hydrostatic pressure. The function of the OmpH protein in adaptation to high pressure and the use of the ompH gene in studying how bacteria sense and respond to pressure is discussed.

Proteins under pressure

“…Although heat-shock treatment confers pressure resistance to yeast (Iwahashi et al, 1991), the well characterized heat-shock response (Lindquist, 1986;Nover, 1991) does not provide means to elucidate the high pressure case. This holds in spite of the fact that a 'pressure-shock response' has been detected at both the protein and mRNA level (Jaenicke et al, 1988;Bartlett et al, 1989;Welch et al, 1993). Biochemical investigations on pressuresensitive systems must be screened for crucial mechanisms of sensitivity, such as dissociatiodcompression of the posttranslocational ribosomal complex, dissociation of multimeric protein assemblies, etc.…”

“…increased solubility of gaseous substrates (H2, CO,) at elevated pressure. In addition, the induction of 'pressure-shock proteins' has been demonstrated by two-dimensional polyacrylamide gel electrophoresis (Jaenicke et al, 1988), as well as on the mRNA level (Bartlett et al, 1989). Attempts to generalize these findings have been made by screening representative examples of all three kingdoms (M. GroB, I. J. Kosmowsky, R. Lorenz, H.-P. Molitoris & R. Jaenicke, unpublished work).…”

An SOS Response Induced by High Pressure inEscherichia coli

“…To date, only a few groups have embarked on dissection of the genetic response of piezotolerant or piezosensitive microorganisms to pressure. For the deep-sea bacterium Photobacterium profundum SS9, Bartlett and colleagues discovered the expression of outer membrane proteins to be pressure dependent and to be regulated at the molecular level by homologues of the Vibrio cholerae ToxR and E. coli RpoE proteins (7,16,53). Using two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gene arrays, two other studies revealed a link between the pressure response and the heat shock or freeze-thaw response of E. coli and Saccharomyces cerevisiae, respectively (30,52).…”

RNA Arbitrarily Primed PCR Survey of Genes Regulated by ToxR in the Deep-Sea Bacterium Photobacterium profundum Strain SS9

“…Whereas the V. cholerae ToxR circuit is controlled by medium salinity and amino acid content and also by temperature and pH in the case of the ToxT branch (37), SS9 ToxR modulation of ompL and ompH expression is controlled by hydrostatic pressure. ompL transcription is optimal at atmospheric pressure, while at 28 MPa ompL expression is low and ompH transcription is derepressed (4,11,12,54,55). Thus, the ToxR system in the piezophilic deep-sea bacterium SS9 appears to have evolved mechanisms for responding to the changes in pressure that the organism encounters as it is moved up or down within the water column.…”

“…Vibrio parahaemolyticus, for example, is a major cause of gastroenteritis associated with seafood consumption (26). Other ToxR-containing bacteria are Vibrio fischeri, a bioluminescent bacterium associated with the light organs of certain fish and squid (16,46), and Photobacterium profundum strain SS9, a deep-sea bacterium originally isolated from amphipod crustaceans (4,14). Since many of the species containing ToxR are nonpathogenic to mammals, and since the ToxR-regulated virulence genes in V. cholerae (but not the toxRS operon) are largely acquired by horizontal gene transfer (27,51), the ToxR regulatory system is not likely to have first evolved for mammalian colonization.…”