Community analysis by Biolog: Curve integration for statistical analysis of activated sludge microbial habitats

Biolog MicroPlates are 96-well plates that contain pre-dried carbon sources and a tetrazolium violet redox dye that turns purple if added microorganisms utilize the nutrients. We have measured absorbance changes due to tetrazolium dye response for microbial communities found in activated sludge and laboratory models of these wastewater communities. To analyze the absorbance versus time data, we export and organize the data into spreadsheets and use a trapezoidal approximation to determine the area under the absorbance versus time curve for each well. The Excel-based trapezoidal approximation has been shown to be in agreement with a more complex curve fitting routine that used SAS to fit a log-logistic function to each curve, and then determined the area under each curve. This data analysis procedure has the advantage of collapsing the absorbance versus time curves down to a single value that integrates information from the entire incubation period. This single value incorporates the lag phase, the rate of development and the extent of dye development for each well. The area under the curve is then used for statistical testing to compare individual carbon source utilization, or in a multivariate pattern analysis of community metabolism of the Biolog MicroPlate carbon sources. Examples of the use of this analysis are given for microbial communities of activated sludge and laboratory models of activated sludge maintained with different types of feedstocks.