Diversity of mat-forming sulfide-oxidizing bacteria at continental margins

Mat-forming sulfide-oxidizing bacteria are intriguing, diverse, highly adapted microorganisms with important biogeochemical functions. As "gradient organisms" they seem to occupy very defined and specialized ecological niches on the seafloor, regarding the availability and concentration of their electron donor sulfide and their electron acceptor oxygen (or nitrate). Many aspects regarding the diversity of mat-forming sulfide oxidizers, as well as the geological drivers favoring massive populations of these organisms, though, require further investigation. In this thesis, five different mat-forming sulfide-oxidizing bacteria were investigated along Europe's continental margins, including giant filamentous Beggiatoa species, giant vacuolated attached filaments (VAF), the giant "sulfur pearl" Thiomargarita, gelatinous-mat-forming Thiobacterium species and filamentous-sulfur-excreting Arcobacter species. The main objectives of this thesis were to expand our knowledge on these conspicuous organisms by the application of molecular techniques targeting their diversity, and the in situ and ex situ investigation of geochemical gradients and parameters that potentially might help to explain the dominance of each sulfide oxidizer in the respective mat habitat.