Our knowledge of microbial diversity and its role in nature is POOf, mainly because traditional microbiological tech- niques, such as microscopy and cultivation, have only a limited use for classification and identification of microor- ganisms. Classification on morphological traits is difficult, because microorganisms are small and look simple, lacking conspicuous external features for a reliable and robust grouping. Furthermore, classification of microorganisms on physiological and biochemical features is nearly impossible, because most, -99%, of all microorganisms in nature can not be isolated in pure cultures mainly due to our ignorance of the culture conditions under which these microorgan- isms thrive in their natural environment [1]. Therefore, for a better understanding of microbial diversity and its role in ecosystem maintenance, other techniques, which comple- ment the microbiological approach, are necessary.