Barophilic growth of bacteria from intestinal tracts of deep-sea invertebrates

Digestive tracts of abyssal scavenging amphipods and a deep-sea holothurian were examined for the presence of intestinal microflora capable of rapid proliferation under in situ pressures of 430 to 520 atmospheres (atm) and temperatures of 3-5°C. For two amphipod specimens, population doubling times of 5 and 6 hours were observed under in situ conditions, compared to 8 and 6 hours, respectively, at 1 atm. Growth enhancement under pressure was related inversely to initial population size and directly to concentration of available nutrient. In the case of the deposit-feeding holothurian, attached bacteria scraped from the intestinal lining showed a doubling time, under pressure, of 11 hours, compared to 36 hours for transient sediment bacteria that comprised the gut contents. These data suggest that deep-sea animals possess a commensal gut flora capable of responding to increased nutrient levels, via feeding of the host, without inhibition by the elevated hydrostatic pressures encountered in the deep ocean environment.