Obligately barophilic bacterium from the Mariana trench

An amphipod (Hirondellea gigas) was retrieved with decompression in an insulated trap from an ocean depth of 10,476 m. Bacterial isolates were obtained from the dead and cold animal by using silica gel medium incubated at 1000 bars (1 bar = 10(5) Pa) and 2 degrees C. The isolate designated MT41 was found to be obligately barophilic and did not grow at a pressure close to that of 380 bars found at average depths of the sea. The optimal generation time of about 25 hr was at 2 degrees C and 690 bars. The generation time at 2 degrees C and 1,035 bars, a pressure close to that at the depth of origin, was about 33 hr. Among the conclusions are: (i) pressure is an important determinant of zonation along the water column of the sea; (ii) some obligately barophilic bacteria survive decompressions; (iii) the pressure of optimal growth at 2 degrees C appears to be less than the pressure at the depth of origin and may be diagnostic for the depth of origin; (iv) rates of reproduction are slow yet significant and an order of magnitude greater than previously thought; and (v) much of deep-sea microbiology may have been done with spurious deep-sea organisms due to warming of samples.