Changes in bacterioplankton metabolic capabilities along a salinity gradient in the York River estuary, Virginia, USA

Changes in metabolic capabilities of bacterial communities along the estuarine salinity gradient may affect the extent of organic matter processing and bacterial growth and accumulation during transit through the system; As part of a larger study of estuarine microbial processes, we attempted to quantify differences in bacterial community structure using Biolog plates. Biolog GN plates (Biolog, Inc., Hayward, CA, USA) were used to determine differences in bacterioplankton community metabolic potential. Biolog GN microplates are 96-well microtiter plates in which each well contains an individual carbon source as well the redox dye tetrazolium violet. As bacteria grow and oxidize each substrate, a purple color is formed that can be quantified spectrophotometrically. The resultant patterns are a function of the original community inoculated into the sample wells. Samples were taken weekly from May 1997 through May 1998 at a fixed location. Samples were also collected bi-monthly from July 1997 through May 1998 at 6 stations located along the salinity gradient. Principal component analysis shows clear differences in the patterns of community metabolic capabilities along the salinity gradient. Bacterial communities were separated by both temperature and salinity. Rates of color development mimicked the pattern of a strong landward gradient in specific growth rates. Biolog analysis is shown to be a powerful tool for identifying shifts in bacterial community composition in space and time, and provides a useful guide for deeper analysis of bulk property data.