"Soda lakes are extreme environments with pH values between 9 and 11, and salt concentrations up to saturation. Despite these hostile conditions, most soda lakes are highly productive and harbor diverse microbial communities responsible for the cycling of chemical elements. The sulfur cycle, driven by haloalkaliphilic sulfur oxidizing bacteria and sulfidogenic bacteria, is one of the most active element cycles in soda lakes. In general, extreme environments are characterized by a low diversity of life. However, we have isolated more than 100 strains of sulfur bacteria from different soda lakes worldwide and detected additional uncultured diversity using molecular techniques. Because life at high salinities and high pH is extremely energy demanding, the enormous diversity of sulfur bacteria in this extreme habitat is a great paradox. The overall goal of the project is to obtain a comprehensive understanding of the diversity and ecophysiology of sulfur bacteria in soda lakes, their niche differentiation, and the molecular mechanisms by which they adapt to extreme halo-alkaline conditions. To achieve this goal, the sulfur bacteria will be studied at the molecular, population and community level, and with a systems biology approach, combining incubation experiments under well-defined conditions, state-of-the-art ‘omics’ techniques, and mathematical modeling. This project will unravel the paradox of the sulfur bacteria in soda lakes, which is not only important for a comprehensive understanding of the success of life under extreme conditions, but also for the use of these bacteria in the sustainable removal of noxious sulfur compounds from our waste streams, which is essential for a clean and healthy environment."