Effect of Hydrostatic Pressure on the Growth of Bacterial Population in Seawater using the Deep-Sea Microbial in-situ Incubation System
Tokuki SAKIYAMA*, Ocky Karna RADJASA, Tsutomu YOSHIDA, and Kouichi OHWADA
Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164, Japan
Growth experiments were conducted with water samples collected from depths of 0, 2000, 4000 and 6000 m at two locations in the northwest Pacific Ocean in order to observe the effect of hydrostatic pressure on the marine bacterial population. When the water samples were incubated under different pressures (0.1, 20, 40, 60 and 80 MPa) at 2℃, higher growth was observed at the pressure levels of the depths where the samples were collected. The results suggest that the bacterial population at each depth would be well adapted to the surrounding pressure condition, as has been suggested by Yayanos (1986) with pure cultured strains isolated from various depths (1).
In our further studies, the Deep-Sea Microbial in-situ Incubation System was developed. The system consists of battery and timer operated peristaltic pumps that can take surrounding water aseptically into eight sterile vinyl bags in which different substrates have been supplied. The system was moored at the depth of 5000 m in the Japan Trench for 285 days. The direct count of the bacterial cells was 6.0 x 103 cells/ml at the beginning, and came up to 1.1 x 108 cells/ml in ZoBell 2216E medium when retrieved. The culture showed growth when it was transferred to a fresh medium under pressurized condition at 3℃. However, it did not show any growth on agar plates or marine broth under atmospheric pressure at 3 and 20℃. The bacterial cells in the surface water (2.1 x 105 cells/ml) decreased to 3.0 x 104 cells/ml when it was retrieved from a depth of 5000 m after 285 days. The surface water sample showed neither any gain of turbidity (600 nm) or any growth non agar plates at 3 and 20℃. The control, surface water in ZoBell 2216E preserved under atmospheric pressure at 3℃, contained 5.2 x 107 cells/mi.
1. Yayanos, A.A. (1986) Proc. Natl. Acad. Sci. USA, 83, 9542-9546.
