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Appl Environ Microbiol. 1975 October; 30(4): 639-649
Copyright © 1975 American Society for Microbiology. All Rights Reserved.

Heterotrophic Activity of Deep-Sea Sediment Bacteria

Department of Microbiology, University of Maryland, College Park, Maryland 20742

ABSTRACT

Sediment samples, containing mixed microbial populations that were decompressed during retrieval from 7,750 and 8,130 m in the Puerto Rican Trench, were recompressed and incubated at the approximate in situ temperature (3 C) and pressure (775 or 815 atm) in the presence of ¹⁴C-labeled amino acids. Heterotrophic activity (total uptake, CO₂ respiration, and cellular assimilation) and cellular-associated "pool" concentrations were measured. Compared with atmospheric controls held at 3 C, the total uptake at elevated pressure at 3 C was reduced, on an average, 55 times, CO₂ respiration was reduced 45 times, and cellular assimilation was reduced 69 times. Rate of total uptake at elevated pressure was found to range from 4.0 x 10^-11 µg/cell per h for leucine to 2.61 x 10^-10 µg/cell per h for an amino acid mixture. Also, the percentage of total uptake at elevated pressures, respired as CO₂, increased at the expense of cellular assimilation (ca. 22% increase). Two cellular-associated amino acid pools were detected, a large, loosely bound, outer pool and a small, tightly bound internal pool. The loosely bound outer pool was removed by a change in the pH of the incubation medium. Even though heterotrophic uptake and the outer, cellular-associated pool were markedly reduced at an elevated pressure, the percentage of total uptake calculated for the unincorporated, tightly bound, intracellular pool was 2 to 19 times that obtained for cultures held at 1 atm. The results were interpreted as indicating that bacterial metabolism and biosynthesis in the deep sea are markedly reduced, with a greater proportion of metabolic activity devoted to cellular maintenance.