USE OF CLUSTER AND DISCRIMINANT ANALYSES TO COMPARE RHIZOSPHERE BACTERIAL COMMUNITIES FOLLOWING BIOLOGICAL PERTURBATION

We present an approach to comparing the diversity and composition of b acterial communities from different habitats and for identifying which members of a community are most affected by an introduced bacterium. We use this method to explore both previously published and new data f rom field and growth chamber experiments in which we isolated heterotr ophic bacteria from samples of root-free soil, roots of nontreated soy bean seedlings, and from the roots of soybean seedlings grown from Bac illus cereus UW85n1-treated seeds. We characterize bacterial isolates for 40 physiological attributes, and grouped the isolates hierarchical ly using two-stage density-linkage cluster analysis. Multivariate anal ysis of variance and discriminant analysis of the relative frequencies of the clusters in the soil and rhizosphere habitats were then used t o determine whether there were differences among the bacterial communi ties from the various habitats, and which of the clusters were most us eful in discriminating among the communities. We used rarefied estimat es of richness as a measure of community diversity in the various habi tats. Introduction of UW85n1 affected the composition and/or diversity of rhizosphere communities in three of four experiments.