Quantitative difference in bacterial abundance determined with each protocol for SYBR Green I and 4′6-diamidino-2-phenylindole (DAPI) methods

Abstract

Bacterial abundance determined with SYBR Green I and 4′6-diamidino-2- phenylindole (DAPI) methods were compared using the protocol for each method employing epifluorescence microscopy. This comparison, using seawater samples that were collected from Sagami Bay, revealed that the abundance determined with the SYBR Green I method was on average 1.6 fold greater than that with the DAPI method. A model 2 regression analysis showed the following relationship: Log SYBR Green I = -0.238+ 1.08 Log DAPI (r2 =0.85, n=68, p<0.0001). These results suggest that when the method is switched between the SYBR Green I and DAPI methods, the difference in bacterial abundance determined by the two methods should be considered for a quantitatively consistent assessment of the bacterial biomass in the ocean. © The Plankton Society of Japan.