Assessment of the effects of nutrients and pollutants on coastal bacterioplankton by flow cytometry and SYTO-13 staining

The specific nucleic acid fluorochrome SYTO-13 was used to assess changes i n density and heterogeneity of marine bacterial populations exposed to nutr ients and common pollutants. Bacterial counts were determined by flow cytom etry calibrated using epifluorescence microscopy and image analysis. The re sults obtained by both methods were significantly correlated. Seawater samp les from a coastal area of Barcelona were incubated for 30 days, after the addition of several pollutants (Hg and surfactants) and organic nutrients. The evolution of bacterioplankton abundance over time was similar in most c ases. It occurred in three phases: (1) a progressive increase in bacterial density; (2) a subsequent decrease, and then (3) a fluctuating stationary p hase. Variations in fluorescence and scatter signals showed changes in the populations of bacteria observed during the evolution of bacterial abundanc e. Bacterioplankton growth or inhibition obtained after exposure to nutrien ts or toxic compounds can be rapidly and easily evaluated by this technique .