Statistical analysis of the time-course of Biolog substrate utilization

Growth of a microbial community on a particular Biolog substrate can be assessed crudely as presence or absence of colour development. More refined is an assessment based on the maximum colour reached after a particular incubation period. The rate of colour development leading up to that maximum can also give useful information about the utilization of the substrate, The statistical analysis and comparison of such time-course profiles is complicated by the multivariate nature of the data. We describe two methods for examining such profiles: 1. a comparison of similarities between profiles from different substrates, using cluster analysis and principal coordinate analysis; 2. an analysis of summary statistics of the profiles, using principal component analysis to identify substrates whose profiles distinguish different treatments. We illustrate these methods with data from a complex microbial community. Cluster analysis and principal coordinate analysis are found to be useful for identifying groups of substrates with similar patterns of reactions. In particular we can identify substrates where no colour development is produced by the microbial communities. The area under the colour development profile summarises the profile in a single statistic, and this may be used in a principal component analysis to identify differences between sample treatments, and the substrates responsible for these. (C) 1997 Elsevier Science B.V.