Regulation of Respiratory Chain Components by Hydrostatic Pressure in a Deep-sea Barophilic Bacterium, Shewanella Sp. Strain DB- 172F
Mohammad H. QURESHI*, Chiaki KATO, and Koki HORIKOSHI
The DEEPSTAR Group, Japan Marine Science & Technology Center, 2-15 Natsushima- cho, Yokosuka-237, Japan
Two obligately barophilic bacterial strains, DB-172F and DB-172R, were isolated recently from a sample of deep-sea sediment from the Izu-Bonin trench, at a depth of 6500 m (1). Phylogenetic studies revealed that both of these barophilic strains belong to the Proteobacteria gamma sub-group arid closely related to the species Shewanella benthica (2). Among the various baroadaptibility mechanisms in a barophilic bacterium, the system for oxidative phosphorylation or respiratory chain mechanism has prime importance because of the sole energy source for the life processes at extreme pressure conditions. ...
In the present study, we first purified a novel ccb-type quinol oxidase enzyme and a cytochrome c-551 from the membrane of DB-172F cells grown at 60 MPa pressure. Whereas from the cells grown at atmospheric pressure (0.1 MPa), a cytoplasmic cytochrome c-552 was isolated. The enzyme quinol oxidase consisted of four kinds of subunits with molecular masses of 98, 66, 18.5 and 15 kDa, respectively, and contained 0.96 mol protoheme and 1.95 mol covalently bound heme c per mol of enzyme. Only protoheme in the enzyme reacted with CO and CN and catalytic activity was 50% inhibited by 4 μM cyanide. This enzyme specifically induced only under hydrostatic pressure conditions and expressed in high content in cells grown at 60 MPa pressure. Cytochrome c-551 consisted of two subunits with molecular weight of 29.1 and 14.7 kDa, respectively, and contained 1.93 mol of heme c per mol of cytochrome. Cytochrome c-551 is constantly expressed at atmospheric pressure and at 60 MPa pressure, but increased up to 1.5 fold in the cells grown at 60 MPa pressure. The cytoplasmic cytochrome c-552 was only expressed at atmospheric pressure and consisted of two subunits with molecular masses of 16.9 and 14.7 kDa, respectively. It contained 0.98 mol of heme c per mol of cytochrome. The isoelectric point of cytochrome c-551 and c-552 were determined to be 4.8 and 4.3, respectively. The enzymatic activity analyses of the membrane from the cells grown at atmospheric pressure and at 60 MPa pressure suggested the presence of two kinds of respiratory chain systems regulating in response to hydrostatic pressure.
1. Kato, C., Masui, N., and Horikoshi K. (1996) J. Mar. Biotechnol., 4, 96-99.
2. Kato, C., Li, L., Tamegai, H., Smorawinska, M., and Horikoshi, K. (1997) Recent Res. Devel. in Agric. & Biol. Cem., 1, 25-31.
