The proposed project aims to sequence the whole genomes of two strains of obligately chemolithoautotrophic, haloalkaliphilic sulfur-oxidizing bacteria. Strain HL-EbGR7, which is closely related to Thioalkalivibro denitrificans, is a low salt-tolerant alkaliphile with an upper salt tolerance of 1.5 M sodium. It was isolated as a dominant sulfide- oxidizing species from a full-scale bioreactor removing sulfide from biogas. The other strain, Thioalkalivibrio sp. K90mix1, is an extremely salt-tolerant alkaliphile, isolated from a soda lake sediment, capable of growth at up to 4M of total sodium and 3.8 M of potassium. We have chosen these strains for whole genome sequencing, because of their industrial relevance in the sustainable removal of sulfur from waste streams and energy carriers. However, the results of the proposed project will be the start of both curiosity- and society-driven research. With these sequences in hand, we are able to obtain a comprehensive understanding of the mechanism by which Thioalkalivibrio strains adapt to extreme haloalkaline conditions. Comparative genomics with neutrophilic counterparts, such as Thiobacillus denitrificans and Thiomicrospira crunogena, will reveal important information on genes responsible for this adaptation and will on the other hand provide insight into the function and evolution of the genes that play a role in common metabolic pathways, such as sulfur-oxidation and carbon assimilation. The use of comparative and functional genomics will show the ecological role and evolutionary history of these bacteria. In addition, functional genomics, i.e. transcriptomics and proteomics, in combination with culture experiments under well-defined conditions in chemostats, will reveal the mechanism and enzymes involved in carbon uptake in haloalkaliphilic chemolithoautotrophs, which is still an enigma. But most important, in particular for society, the whole genome sequences of both bacteria will give the opportunity to create genomic tools, such as DNA microarrays, to study the diversity and physiology of these microorganisms in natural and engineered ecosystems. These tools are essential to improve the performance of these bacteria in the sustainable removal of reduced sulfur compounds from waste streams and energy carriers (i.e., natural gas and biogas), which is mandatory for a clean and healthy environment, and fits to the mission of the DOE.