Isolation and Characterization of a Barotolerant Bacterium KT 1018 from Okushiri Ridge
Osamu TAKEI*a, Tetsushi KOMATSUb, Akira INOUEb, Ron USAMIa, and Koki HORIKOSHIa,b
a Department of Applied Chemistry, Faculty of Engineering, Toyo University, 2100 Kujirai, Kawagoe 350, Japan
b The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15 Natsushima- cho, Yokosuka 237, Japan
The deep-sea environment is charactreized by high hydrostatic pressure, darkness and low temperature. Pressure influences bacterial growth (1), for example cell elongation was observed in E. coli cultivated at 20 MPa, however it did not grow at 50 MPa (2). Several kinds of barophilc and barotolerant bacteria which grow well under high pressures have been isolated from deep sea samples, which has raised interest in pressure adaptation mechanisms. Unfortunately, almost all isolates are psychrophilic, so they have slow growth rates and reach low cell densities. It is therefore difficult to prepare a large cell mass for the investigation of specific mechanisms. To overcome this problem, we have tried to isolate bacteria which grow faster and reach higher cell densities under high pressure.
Screening of such microorganisms was carried out at 50 MPa at 25℃. KT1018 was isolated from an Okushiri ridge mud sample collected at a depth of 500 m. The strain grew at up to 60 MPa in a complex medium. KT1018 is a mesophilic barotorelant bacterium which is identified as vibrio Sp. based on its physiological and morphological characteristics. It grew at a temperature range of 4 to 37℃, pH of 5 to 9 and 0 to 4% NaCl. This strain grew well at up to 40 MPa with a final cell density of 0.33 at OD660. Cell elongation which was reported in E. coli was not observed. The effect of culture conditions such as temperature, ingredients and pH of medium on growth under high pressure were studied. Although cultivation temperature and initial pH of the medium did not influence growth, strain KT1018 was unable to grow at 50 MPa without adding NaCl. Among metal salts tested MgCl2 showed a considerable effect on pressure adaptation similar to that of NaCl, however, MgCl2 did not further enhance growth in the presence of 3% NaCl. These observations suggest that NaCl and MgCl2 play an important role in increased pressure tolerance in KT1018. We are now investigating how these two metals are involved in the pressure adaptation of this strain.
1. Zobell C.E. et al., (1949) J. Bacteriol., 57, 179-189.
2. Tamura K. et al., (1992) FEMS Microbiol. Lett., 99, 321-324.
