Unraveling predatory prey interactions between bacteria It is known for decades that certain bacteria are capable to use other bacteria as nutrient sources. As a matter of fact predatory behavior is not uncommon in prokaryotes. Predatory bacteria were found both in terrestrial and in aquatic habitats. To date however only a few of these micropredators have been thoroughly characterized with regard to their ecology and predation strategies. In this study various aspects of the predatory behavior of the hitherto hardly investigated genera Lysobacter and Cupriavidus should be explored. The first goal was to develop tools for investigating the predatory performance of Lysobacter and Cupriavidus strains under laboratory conditions. Since predatory bacteria pursue many different hunting strategies the design of a generally applicable assay was challenging. Available predation assays are tailored to predator specific features such as growth rate motility and prey range. The best characterized facultative predators are myxobacteria and several predation assays have been established for this bacterial group. Because myxobacterial predation assays were found to be not suitable for testing of Lysobacter and Cupriavidus strains an alternative predation assay was developed that provides quantitative data on the reduction of bacterial prey and the concomitant growth of the predator. For this purpose as prey soil bacteria that produce distinctive pigments or harbor specific antibiotic resistant gene were selected. Following a defined period in which the prey bacteria were incubated together with the predator the individual populations could easily be distinguished based on the colors of their colonies or antibiotic resistance after plating. With CFU based predation assay the predatory activity of both genera was verified. Lysobacter spp. and Cupriavidus spp. were shown to consume both Gram negative and Gram positive bacteria. The second aim was to identify factors that trigger and promote predatory activity. Using the CFU based predation assay it was confirmed that the selected Lysobacter spp. were effectively feeding on both Gram positive and Gram negative prey under nutrient deficient conditions