During WELLMA-DNA, 13 diploma and bachelor theses along with several internships have been completed. A sampling system for biofilm samples as well as a sampling device for water samples have been designed and tested. More than 400 DNA samples of different well sites have been collected and analyzed. Microbiological and molecular methods have been combined to gain a better understanding of the community composition of the ochre forming biofilms inside the wells. Molecular methods included PCR, DGGE, cloning and sequencing. During the project, the bacterial populations of an unprecedented number of wells have been analyzed and several indicator bacteria for iron-related well clogging have been identified. Alongside iron-oxidizing bacteria, iron-reducing bacteria have been found in the wells and their potential for ochre-solubilization was confirmed. Alongside the molecular experiments, microbiological trials included the isolation of pure cultures, microscopic analysis and physiological tests. The morphology of the encountered iron bacteria could be classified into four different groups, which may have an impact on the rigidity of the biofilms on a macroscopic level. We were able to cultivate several of these indicator organisms, which could play an important role in the formation of ochreous deposits in the Berlin wells. During experiments utilizing microscopic flow cells, differences in growth rate and patterns of these ochre-forming bacteria have been observed. For several of the identified indicator bacteria, primers have been calculated. These primers will allow for the first time to quantify the amount of indicator bacteria in a water sample and to derive operational pointers. In addition, several experiments regarding the effect of hydrogen peroxide on ochre forming biofilms have been conducted and the effect of an additional electron donor (ethanol) on the communities has been tested. For future data acquisition and documentation, a guideline for classifying the degree of pump clogging has been developed.