Microautoradiography study of thymidine uptake in brackish waters around Sapelo Island, Georgia, USA

Abstract

[Total cell numbers, thymidine uptake rates, and percent of bacteria labeled with thymidine were determined in a variety of brackish water environments around Sapelo Island. Cell numbers were high compared to other aquatic habitats and varied between 4 × 10⁶ and 3.2 × 10⁷ cells ml⁻¹ (average 1.07 × 10⁷ cells ml⁻¹). Thymidine uptake rates were also among the highest published values, up to 425 fmol thymidine ml⁻¹ h⁻¹ (average 213 fmol thymidine ml⁻¹ h⁻¹). Despite high abundance and activity, the percentage of cells labeled with thymidine (as determined by micro-autoradiography) was usually low, ranging from 1 to 69 % (average 16 %). Brackish-water cultures studied in the laboratory showed, at most, 57 % of the bacteria labeled even during exponential growth. Therefore, it was concluded that many actively growing cells did not take up thymidine in these waters. Implications for productivity estimates from thymidine uptake rates are discussed.]