Relative effectiveness of kinetic analysis vs single point readings for classifying environmental samples based on community-level physiological profiles (CLPP)

The relative effectiveness of average-well-color-development-normalized sin gle-point absorbance readings (AWCD) vs the kinetic parameters mu (m), lamb da, A, and integral (AREA) of the modified Gompertz equation tit to the col or development curve resulting from reduction of a redox sensitive dye from microbial respiration of 95 separate sole carbon sources in microplate wel ls was compared for a dilution series of rhizosphere samples from hydroponi cally grown wheat and potato ranging in inoculum densities of 1 x 10(4) - 4 x 10(6) cells ml(-1). Patterns generated with each parameter were analyzed using principal component analysis (PCA) and discriminant function analysi s (DFA) to test relative resolving power. Samples of equivalent cell densit y (undiluted samples) were correctly classified by rhizosphere type for all parameters based on DFA analysis of the first five PC scores. Analysis of undiluted and 1:4 diluted samples resulted in misclassification of at least two of the wheat samples for all parameters except the AWCD normalized (0. 50 abs. units) data, and analysis of undiluted, 1:4, and 1:16 diluted sampl es resulted in misclassification for all parameter types. Ordination of sam ples along the first principal component (PC) was correlated to inoculum de nsity in analyses performed on all of the kinetic parameters, but no such i nfluence was seen for AWCD-derived results. The carbon sources responsible for classification differed among the variable types with the exception of AREA and A, which were strongly correlated. These results indicate that the use of kinetic parameters for pattern analysis in CLPP may provide some ad ditional information, but only if the influence of inoculum density is care fully considered. (C) 2001 Elsevier Science Ltd. All rights reserved.