Microbial activities in undecompressed and decompressed deep-seawater samples.

Microbial transformations of C-labeled substrates (sodium glutamate, Casamino Acids, glucose, and sodium acetate) were measured in undecompressed seawater samples collected from depths of 1,800 to 6,000 m, during 14- to 21-day incubation periods at in situ temperature (3 degrees C). Each substrate was tested at two concentrations (ca. 0.5 and 5.0 mug/ml) and two in situ pressures. The data were compared to 1-atmosphere (ca. 1.013 x 10 kPa) controls. The rates of C incorporation and CO(2) production as well as the amounts of total substrate utilization were generally lower at pressure than in the decompressed controls but were significantly different for each of the four substrates used. The utilization of acetate was the least affected by pressure; rates were similar to those measured at 1 atmosphere in two out of four experiments. In contrast, transformation rates of the amino acids at pressure averaged to only 38% of those in the controls. A single but reproducible "barophilic" response was observed with glucose as a substrate in samples collected from a depth of 4,500 m at a specific area in the northwestern Atlantic Ocean. Except for this latter set of experiments, the transformation of all substrates showed an increased lag period at pressure as compared to the 1-atmosphere controls.