Ecology and evolution of bacterial microdiversity

Using high resolution molecular fingerprinting techniques like random ampli fication of polymorphic DNA. repetitive extragenic palindromic PCR and mult ilocus enzyme electrophoresis, a high bacterial diversity below the species and subspecies level (microdiversity) is revealed. It became apparent that bacteria of a certain species living in close association with different p lants either as associated rhizosphere bacteria or as plant pathogens or sy mbiotic organisms, typically reflect this relationship in their genetic rel atedness. The strain composition within a population of soil bacterial spec ies at a given field site. which can be identified by these high resolution fingerprinting techniques, was markedly influenced by soil management and soil features. The observed bacterial microdiversity reflected the conditio ns of the habitat, which select for better adapted forms. In addition, infl uences of spatial separation on specific groupings of bacteria were found, which argue for the occurrence of isolated microevolution. In this review: examples are presented of bacterial microdiversity as influenced by differe nt ecological factors. with the main emphasis on bacteria from the natural environment. In addition. information available From some of the first comp lete genome sequences of bacteria (Helicobacter pylori and Escherichia coli ) was used to highlight possible mechanisms of molecular evolution through which mutations are created, these include mutator enzymes. Definitions of bacterial species and subspecies ranks are discussed in the light of detail ed information from whole genome typing approaches. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.