COMPARISON OF BLUE NUCLEIC-ACID DYES FOR FLOW CYTOMETRIC ENUMERATION OF BACTERIA IN AQUATIC SYSTEMS

Seven blue nucleic acid dyes from Molecular Probes Inc, (SYTO-9, SYTO- 11, SYTO-13, SYTO-16, SYTO-BC, SYBR-I and SYBR-II) were compared with the DAPI (4',6-diamidino-2-phenylindole) method for flow cytometric en umeration of live and fixed bacteria in aquatic systems. It was shown that SYBR-II and SYTO-9 are the most appropriate dyes for bacterial en umeration in nonsaline waters and can be applied to both live and dead bacteria, The fluorescence signal/noise ratio was improved when SYTO- 9 was used to stain living bacteria in nonsaline waters. Inversely, SY BR-II is more appropriate than SYTO dyes for bacterial enumeration of unfixed and fixed seawater samples.