Microscopy and ecophysiological investigations of marine sulfur bacteria

Abstract

Central to the research presented here are the group of “colorless sulfur bacteria,” terminology dating back to shortly after Sergei Winogradsky introduced “sulfur bacteria” in the late 19th century. The majority of known colorless sulfur bacteria reside within the Proteobacteria phylum, notably within the Gammaproteobacteria class. These organisms inhabit a wide range of ecological niches including acid mine drainage, hypersaline/alkaline lakes, hydrothermal vents, cold seeps and coastal upwelling zones, and ice-covered Antarctic lakes, often forming conspicuous mats. Thus, these bacteria are often found inhabiting gradients at the interface between anoxic, often sulfide rich sediments, and aerobic top water. The spatial separation of primary electron donors (sulfide) and acceptors (oxygen and nitrate) has pressured some sulfur oxidizers to develop strategies and/or relationships that afford them access to said electron donors and acceptors; some of which are realized in their unique morphologies. This is exemplified in the large, colorless sulfur bacteria belonging to the gammaproteobacterial family, Beggiatoaceae. At the time of writing, no vacuolated large sulfur bacteria have been isolated in pure culture. Thus, what is known about their physiologies, unique morphologies, and ecological relationships is predominately the result of decades worth of culture-independent and in situ studies. This dissertation is split into three separate but related studies. The first study investigated the potential for sulfur-oxidizing bacteria to influence authigenic carbonate dissolution in marine cold seep settings and discuss the potential impact on the global carbonate rock reservoirs. The second study delved into the complex cytoskeletal network within the large sulfur bacterium, Ca. Thiomargarita spp., and revealed the presence of vesicle like features that contain peptidoglycan and outer membrane components. Furthermore, genomes revealed homologs to genes associated with phagocytosis in eukaryotes, which were further investigated via actin-labeling and fluorescence microscopy, revealing actin-like features associated with sulfur globules and vesicles. Lastly, as the physiological role these intracellular vesicles remain unknown, the third and final study utilized live cell microscopy, immunofluorescence, actin labeling, and protein analyses to identify potential functions of these vesicles.