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Tritiated thymidine incorporation and the growth of heterotrophic bacteria in warm core rings 1
Author(s) -
Ducklow Hugh W.,
Hill Suzanne M.
Publication year - 1985
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1985.30.2.0260
Subject(s) - heterotroph , seawater , bacteria , thymidine , bacterial growth , growth rate , biology , population , estuary , environmental chemistry , chemistry , ecology , biochemistry , in vitro , genetics , geometry , mathematics , demography , sociology
The time‐course of the incorporation rate of [methyl‐ 3 H]thymidine ([ 3 H]TdR) was established during 6–12‐h incubations of natural bacterial populations sampled from the surface layers of warm core Gulf Stream rings. Parallel estimates of changes in cell numbers were made in order to examine the relationships between TdR incorporation and population growth for oceanic bacterial populations. Our results indicate that a conversion factor of 4 × 10 18 cells produced per mole of [ 3 H]TdR incorporated yielded estimates of bacterial production which were within a factor of 2 or 3 of production estimates derived from changes in cell numbers in seawater cultures. We observed a significant, direct relationship between the initial rates of TdR incorporation per cell and specific growth rates and conclude that initial short term (15–45 min) assays of TdR incorporation are a valuable tool for studying bacterial production in oceanic waters. In most incubations, the rate of TdR incorporation increased more rapidly than did cell numbers. Analyses of the time‐courses of TdR incorporation rates yielded estimates of specific growth rates for the actively dividing bacteria ranging from 0.08 to 0.51 h −1 . Very large conversion factor values were derived from these data. The discrepancy between “growth” determined from TdR incorporation rates and total bacterial numbers in seawater cultures has not been observed in previous studies of coastal, estuarine, or lacustrine bacteria, but was a consistent feature of our studies on oceanic populations. We suggest that this may reflect the opportunistic character of oligotrophic bacteria. Rapid enhancement of TdR incorporation may indicate the capability of oligotrophs to grow rapidly when favorable conditions arise.