Improved Method of Enumeration of Attached Bacteria for Study of Fluctuation in the Abundance of Attached and Free-Living Bacteria in Response to Diel Variation in Seawater Turbidity

ABSTRACT

Sample preparation for enumerating attached bacteria in turbid seawater by epifluorescence microscopy was improved by treating samples with a surfactant (Tween 80) followed by sonication. With optimal treatment with Tween 80 (final concentration, 10 ppm [10 μg/ml]) and sonication, as many as 10 times more attached bacteria were enumerated from turbid seawater relative to the number enumerated from an untreated control. Dispersion of bacteria by sonication alone resulted in the enumeration of only 42 to 72% of the attached bacteria. By this technique, fluctuations in the number of attached and free-living bacteria were determined in water from Aransas Pass, Tex., where surface sediments are resuspended on a regular basis by tidal currents. The abundance of attached bacteria increased in proportion to the seawater turbidity that resulted from sediment resuspension. The variation in abundance of free-living bacteria was not directly related to seawater turbidity. However, the magnitude of fluctuation in the abundance of free-living bacteria was related to the extent of turbidity variation during diurnal tides.