Analysis of bacteria in aquatic environments using sedimentation field-flow fractionation: (I) biomass determination

Sedimentation field-flow fractionation (SdFFF) is a new method for characterizing heterotrophic bacteria in aquatic environments. SdFFF separates bacteria on the basis of the buoyant mass of the cells, and so biomass per cell can be directly determined at each point across the fractionation. The only datum required for this calculation is the average specific gravity of the cell organic matter. When an estimate of the cell number concentration in fractions across the SdFFF separations is made then the biomass distribution and total bacterial biomass of the sample can be determined directly. The SdFFF method has the potential to provide more accurate bacterial biomass data than existing methods which require the use of a biomass:biovolume conversion factor. It is also less time consuming and tedious than measuring the biovolume by microscopy. In this paper the method is tested for the first time to make estimates of the bacterial biomass in natural waters. Samples from four distinctly different environments were analyzed namely, sea water, an urban lake, a billabong (oxbow lake) and a wastewater containing sewage.