Mechanisms of Gene Expression Controlled by Pressure in Deep-sea Microorganisms
Chiaki KATO*, Kaoru NAKASONE, Maria SMORAWINSKA, Takako SATO, Lina LI, Hideyuki TAMEGAI, and Koki HORIKOSHI
The DEEPSTAR Group, Japan Marine Science and Technology Center, 2- 5 Natsushima-cho, Yokosuka 237, Japan
The deep-sea is an extreme environment typified by high pressure and low temperature. Microorganisms in the deep-sea are adapted to this environment and they may have unique mechanisms for gene expression controlled by high pressure. To investigate the deep-sea adaptation mechanisms in bacteria, we have isolated numbers of bacteria displaying barophilic or piezophilic, and barotolerant or piezotolerant growth properties from the deep-sea sediment samples obtained by the manned and unmanned submersibles, "Shinkai 6500" and "Kaiko" operated by JAMSTEC (1,2).
A pressure-regulated operon has been cloned and sequenced from both deep-sea barophilic and barotolerant strains, DB6705 and DSS12, which belong to a distinct subgroup of the genus Shewanella, referred to as the "barophiles branch" (3). To understand the pressure-regulated mechanisms in gene expression, the upstream element of the pressure-regulated operon from Shewanella sp. strain DSS 12 was studied under several pressures. Regions A and B were classified by sequence analysis. A unique octamer motif AAGGTAAG, was found to be tandemly repeated 13 times in region B. An electrophoretic mobility shift assay demonstrated thatσ54-like factor recognized region A and other unknown factors recognized region B. Different shift patterns of the protein-DNA complexes were observed when cell extracts cultured at 0.1 MPa and 50 MPa were incubated with the DNA probe of region B. These results indicate that the deep-sea strain DSS12 expresses different DNA-binding factors under different pressure conditions.
Downstream of the pressure-regulated operon, other pressure-regulated genes were discovered, the first gene was identified as cydD based upon its deduced amino acid sequence and heterologous complementation studies in Escherichia coli. In E. coli, CydD is required for the assembly of the cytochrome bd complex, one of the components of the aerobic respiratory chain. E. coli cydD mutants display increased sensitivity to high pressure, but can be converted to wild type levels of high pressure sensitivity in strains bearing the DSS 12 cydD on a plasmid (4). We observed that the cytochrome bd complex protein was detected only from high pressure cultivation in strain DSS 12 by spectrophotometric analysis (5). Further, cydD seems to function to
