H. Weyland

Psychrophilic versus psychrotolerant bacteria--occurrence and significance in polar and temperate marine habitats.

The numerical dominance and ecological role of psychrophilic bacteria in bottom sediments, sea ice, surface water and melt pools of the polar oceans were investigated using isolates, colony forming units (CFU) and metabolic activities. All sediment samples of the Southern Ocean studied showed a clear numerical dominance of cold-loving bacteria. In Arctic sediments underlying the influence of cold polar water bodies psychrophiles prevailed also but they were less dominant in sediments influenced by the warm Atlantic Water. A predominance of psychrophiles was further found in consolidated Antarctic sea ice as well as in multiyear Arctic sea ice and in melt pools on top of Arctic ice floes. A less uniform adaptation response was, however, met in polar surface waters. In the very northern part of the Fram Strait (Arctic Ocean) we found bacterial counts and activities at 1 degree C exceeding those at 22 degrees C. In surface water of the Weddell Sea (Southern Ocean) psychrophiles also dominated numerically in early autumn but the dominance declined obviously with the onset of winter-water and a decrease of chlorphyll a. Otherwise in surface water of the Southern Ocean CFUs were higher at 22 degrees C than at 1 degree C while activities were vice versa indicating at least a functional dominance of psychrophiles. Even in the temperate sediments of the German Bight true psychrophiles were present and a clear shift towards cold adapted communities in winter observed. Among the polar bacteria a more pronounced cold adaptation of Antarctic in comparison with Arctic isolates was obtained. The results and literature data indicate that stenothermic cold adapted bacteria play a significant role in the global marine environment. On the basis of the temperature response of our isolates from different habitats it is suggested to expand the definition of Morita in order to meet the cold adaptation strategies of the bacteria in the various cold habitats.

Effect of hydrostatic pressure and temperature on the activity and synthesis of chitinases of Antarctic Ocean bacteria

The formation of chitinases by psychrophilic and psychrotrophic marine Antarctic bacteria and the activity of these extracellular enzymes were investigated under simulated deep-sea conditions. The formation of the chitinases was affected by hydrostatic pressure of 400 bars. However, the extent of pressure inhibition differed with the bacterial strains tested and was considerably less with the extreme psychrophilic bacteria isolated from sediments of greater depth. Growth of these psychrophilic strains had a moderately barophilic character at 400 bars, whereas growth of the psychrotrophic strains was clearly restricted under simulated deep-sea conditions. With regard to the activity of the extracellular chitinases of various bacterial strains, a relatively uniform response was found. All chitinases were highly barotolerant at near neutral pH and were active up to 1000 bars. Low temperatures reduced their activity but not their barotolerance. A low pH of 5.1 diminished the barotolerance of some chitinases. The results suggest that the indigenous deep-sea bacteria are capable of decomposing chitin settled to or produced in the depth of the Antarctic Ocean.