Microbial life in pelagic sediments: the impact of environmental parameters on enzymatic degradation of organic material

Abstract

The impact of environmental parameters, such a s salinity, temperature, pressure, and nutrients, on microbial actlvity was investigated in pelagic sediments of the Norwegian-Greenland Sea (water depth between 1400 and 2000 m) As a general characteristic of benthic microbial activity, the enzymatic degradation of organic material, which represents the initial and rate-limiting step in carbon oxidation, was measured. For the enzyrnatic analysis, fluoresceindiacetate was used, a fluorogenic model substrate which is hydrolyzed non-specifically by hydrolytic enzymes. The substrate was added at saturation level, and potential enzymatic activity rates were derived from the slope of the linear part of time-dependent activity curves. From the investigations i t can be concluded that the pool of hydrolytic enzymes in the pelagic sediments was not specifically adapted to ambient parameters such as salinity, temperature, and pressure. There was no indication of a psychrophilic and/or barophilic response. Enzymatic degradation of organic material was more regulated by the supply of organic material than by cold temperature and elevated pressure. Boiled detritus added to sediment cores incubated under in situ temperature on board ship caused an immediate stimulation of hydrolytic enzymes. The location of microorganisms in the sediment and the unique characteristics of microbial metabol~sm must both be considered as possible strategies for using the incoming organic material effectively and for surviving the long periods of nutrient deficiency in pelagic sediments.