A PRESSURIZED CHEMOSTAT FOR THE STUDY OF MARINE BAROPHILIC AND OLIGOTROPHIC BACTERIA

A continuous culture system that allows bacteria to be grown in steady -state populations under pressures of up to 700 atm (71 MPa) was const ructed and tested, With readily available or slightly modified high-pr essure chromatography equipment, a continuous flow of sterile medium i s pressurized and passed through a 500-ml nylon-coated titanium reacto r at dow rates of 0.01 to 10 ml min(-1). The pressure in the reactor i s controlled by a backpressure regulator with greater than 1% accuracy , In test experiments, a culture of a psychro- and barophilic marine i solate from a depth of 4,900 m (strain F1-A, identified as a Shewanell a sp,) was grown at 1, 300, and 450 atm (0.1, 30.4, and 40.5 MPa) and dilution rates of 60 and 90% of the organism's maximum growth rate (de termined at 1 atm) in the required complex medium at levels of 3.3 and 0.33 mg of dissolved organic carbon per liter in the reservoir, Growt h limitation by carbon was assured by an appropriate C/N/P ratio of th e medium. The data indicate that barophilic growth characteristics in steady-state cultures of this psychro- and barophilic deep-sea isolate were positively affected by a decreasing growth th rate at the higher of two substrate concentrations in the reservoir. After a 10-fold low ering of the substrate concentration, the effect was reversed, Under t hese conditions, the cell viability increased significantly, especiall y at the higher of the two pressures tested, The basic design of the s ystem can principally also be used for growth studies on hyperthermoph ilic bacteria and archaea.