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

Abstract

The specific nucleic acid fluorochrome SYTO-13 was used to assess changes in density and heterogeneity of marine bacterial populations exposed to nutrients and common pollutants. Bacterial counts were determined by flow cytometry calibrated using epifluorescence microscopy and image analysis. The results obtained by both methods were significantly correlated. Seawater samples 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 cases. It occurred in three phases: (1) a progressive increase in bacterial density; (2) a subsequent decrease, and then (3) a fluctuating stationary phase. Variations in fluorescence and scatter signals showed changes in the populations of bacteria observed during the evolution of bacterial abundance. Bacterioplankton growth or inhibition obtained after exposure to nutrients or toxic compounds can be rapidly and easily evaluated by this technique.