Comparison of bromodeoxyuridine immunoassay with tritiated thymidine radioassay for measuring bacterial productivity in oceanic waters

Recently, bromodeoxyuridine (BrdU) has been successfully applied to the measurement of bacterial productivity as an alternative to tritiated thymidine (H-3-TdR), which is widely used but often restricted by regulations, particularly in field settings. Here, I report improvements to existing BrdU methods to simplify procedures and increase sensitivity. The feasibility of the method was tested measuring bacterial production in low-productive waters. The method provided radioisotope-free measurements of bacterial production rates at shorter (similar to 1 h) on-board processing time of samples than previously reported procedures. It was applicable to the detection of rates ranging from 0.021 to 2.7 pmol BrdU I(-1)h(-1). BrdU incorporation rates measured by immunoassay showed a statistically significant correlation with H-3-TdR incorporation rates measured by radioassay (r = 0.74, n = 24, p < 0.001). The linear regression obtained (BrdU = 0.80[H-3-TdR] - 0.016) showed a similar relationship to previously reported regressions (BrdU = 0.65 [H-3-TdR] + 0.12, [H-3-BrdU] = 0.69[H-3-TdR] - 0.81). There were no statistically significant differences among these regression lines. These results suggest that the method described here provides a non-radioisotopic productivity measurement of bacteria in oceanic epipelagic waters, while retaining continuity of the data with other existing H-3-TdR and BrdU methods.