The Isolation and Characterization of a Novel Haloalkaliphilic Purple Sulfur Bacterium, Ectothiorhodospira monomense, sp. nov., from Mono Lake

Life exists in a wide range of environments with prokaryotic organisms inhabiting those considered most hostile, including extremes of temperature, salinity, water activity, and pH. The microorganisms that inhabit these extreme environments, and in particular anoxygenic phototrophs that inhabit salt and soda lakes, are the focus of this thesis. These environments are typified by (1) high salinity, and the associated problem of a hypoosmotic external environment, and (2) an alkaline environment, where the cell's membrane potential is disrupted. In the present study, a novel purple sulfur bacterium of the genus Ectothiorhodospira was isolated from the highly saline (8%) highly alkaline (pH 8-10) Mono Lake in Mono County, CA. This isolate exhibited optimal growth under photoheterotrophic conditions at 1.4 M NaCl and pH 9.4, and possessed many metabolic properties unique among related organisms. The classification of the organism isolated in this study, Ectothiorhodospira strain MLS1, as a novel species, Ectothiorhodospira monomense (N.L. adj. pertaining to Mono Lake), is thus proposed. This thesis describes the isolation and characterization of this organism, and lays the foundation for future studies of its metabolism and genetics, including aspects of nitrogen and carbon fixation; as well as the synthesis, regulation and stability of cell wall and cell membrane components under highly saline and alkaline conditions.