[en] Contamination of drinking water with arsenic can be measured in laboratories with atom absorption spectrometry (AAS), mass spectrometry with inductive coupled plasma (ICP-MS) or atom fluorescence spectrometry (AFS) at the relevant concentrations below 50 μg/L. Field test kits which easily and reliably measure arsenic concentrations are not yet available. Test systems on the basis of bioreporter bacteria offer an alternative. Based on the natural resistance mechanism of bacteria against arsenic compounds toxic for humans, bioreporter bacteria can be constructed that display arsenic concentrations with light emission (luminescence or fluorescence) or colour reactions. This is achieved by coupling the gene for the ArsR-protein and arsenic regulated promoters with suitable reporter genes. The resulting bioreporter bacteria report bioavailable arsenic in a dose dependent manner at the toxicologically relevant level of 2 to 80 μg/L and are therewith suitable both for the guideline levels of the WHO of 10 μg/L and for the national standards in South East Asia of 50 μg/L. This alternative method has the advantage of being independent from sophisticated apparatus as by eye detection is feasible and offers the possibility of measuring directly the bioavailable fraction. Bioreporter bacteria are also suitable for in situ research. Yet, in order to apply such bioreporter bacteria as a low-cost analytical tool in a regular manner, open questions exist regarding the preservation of the specific activity, the vitality of bioreporter bacteria and the improvement of bioreporter test systems for layman. The aim of this thesis hence was to optimize and improve bioreporter based test systems to allow easy conservation, storage and transport, and also an application without the need of a sophisticated infrastructure. For that purpose it was intended (i) to develop and validate a method that allows arsenic detection without external calibration (chapter 2) and (ii) to improve the vitality and specific activity of preserved bioreporter bacteria by using different conservation methods and culture conditions (chapter 3). A further goal was (iii) to use arsenic bioreporter bacteria for the detection of arsenic in the rhizosphere of maize plants in order to investigate transport processes and understand resistance mechanisms of plants (chapter 4). To achieve this, different strains of the bioreporter bacteria Escherichia coli DH5α were used in well defined experiments to receive reproducible results. Zea mays L. was used as a model plant in easily accessible rhizoboxes. The main outcome of this thesis is: (i) A multiple cell line approach was developed that permits detection of arsenic without external calibration (chapter 2). For this purpose two different kind of reporter constructions were developed and modified that resulted in strains which differ in their sensitivity against arsenic. Because of this each bioreporter strain starts the visible reaction at a different concentration and in combination the strains display the arsenic concentration at relevant levels. (ii) A preservation method based on vacuum drying with addition of 34% trehalose and 1.5% polyvinylpyrrolidone could be identified that preserved the specific activity and vitality of the bioreporter bacteria over a time range of 12 weeks and that allows their application for over night measurements (chapter 3). (iii) A carrier system for bioreporter bacteria was developed which facilitates the investigation of arsenic distribution in the rhizosphere. It could be shown that the distribution along roots is dependent on the root age and structure (chapter 4). Mainly at laterals and on roots tips higher concentrations of arsenic were detected. In addition a split root experiment indicated that arsenic is translocated within the roots and released also by intact roots. This thesis shows that bioreporter based test systems can be improved to achieve broad application in low-cost laboratory monitoring as well as in in situ experiments thus proving that they are a valuable tool for environmental research and a promising alternative to existing methods. (orig.)