APPLICATION OF THE NOVEL NUCLEIC-ACID DYES YOYO-1, YO-PRO-1, AND PICOGREEN FOR FLOW CYTOMETRIC ANALYSIS OF MARINE PROKARYOTES

Novel blue light-excited fluorescent dyes for nucleic acids (YOYO-1, Y O-PRO-1, and PicoGreen) were tested on cultures of Escherichia coli an d of a variety of marine prokaryotes. Results of flow cytometric DNA a nalyses were compared with those obtained with the UV-excited dyes bis -benzimide Hoechst 33342 or 4',6-diamidino-2 -phenylindole (DAPI), YOY O-1, YO-PRO-1, and PicoGreen can be used only on aldehyde-fixed cells and need to be supplemented with cofactors such as potassium, citrate, or EDTA, They are highly sensitive to ionic strength. Consequently, s eawater culture samples cannot be stained directly with these dyes and require at least a 10-fold dilution with distilled water to obtain re liable fluorescence signals. After treatment with RNase, coefficients of variation for the G(1) peak of the DNA distributions of the differe nt strains tested with YOYO-1 or PicoGreen indicated in general an imp rovement dyer Hoechst 33342 staining, These novel dyes can be used to enumerate prokaryotic cells by flow cytometry, as demonstrated with E. coli. However, their sensitivity to ionic strength makes them unsuita ble for cell cycle analysis in natural samples.