For a long time microbial ecology has been developed as a distinct field with in Ecology. In spite of the important role of microorganisms in the environ ment, this group of 'invisible' organisms remained unaccessable to other ecologists. Detection and identification of microorganisms remain largely dependent on isolation techniques and characterisation of pure cultures. We now realise that only a minor fraction of the microbial community can be cultivated. As a result of the introduction of molecular methods, microbes can now be detected and identified at the DNA/RNA level in their natural...