The basic research question 'How gradients and transition zones, especially in relation to water availability, do shape microbial communities in extreme ecosystems?' is addressed through the following topics: 1) Plant- and animal-microbe interactions in arid lands 2) The role of microbes in sustaining the mangrove biome 3) Adaptation of oil HC degraders to the Red Sea 4) Microbial stratification in the Red Sea deep brine pools 5) Dissecting ecosystem functioning through Synthetic Ecology