Physiology of alkaliphilic sulfur-oxidizing bacteria from soda lakes

The inorganic sulfur oxidation by obligate haloalkaliphilic chemolithoautotrophs was only recently discovered and investigated. These autotrophic sulfur oxidizing bacteria (SOB), capable of oxidation of inorganic sulfur compounds at moderate to high salt concentration and at high pH, can be divided into three genera belonging to the γ subdivision of the Proteobacteria: Thioalkalimicrobium, Thioalkalivibrio and Thioalkalispira. Their taxonomy, metabolic diversity and the potential application in biological removal of toxic sulfur compounds of haloalkaliphilic SOB were reviewed in Chapter 1 (Introduction) of this thesis. The scope of this thesis was to characterize the physiology and growth kinetics of the newly isolated haloalkaliphilic chemolithotrophic SOB with respect to their potential use in the biotechnology of H2S removal under haloalkaline conditions. A second aim of this thesis was to obtain more information about the specific adaptation to high salt and alkaline conditions from the population level down to the biomolecular level. The growth physiology of representatives of the genus Thioalkalimicrobium and Thioalkalivibrio is compared in Chapter 2. The competitive interaction between these two groups of organisms and their survival strategy with direct implications in their ecology is also described. The Chapter 3 describes the sodium salt requirement for the growth and sulfur-oxidizing potential at alkaline conditions in Thioalkalivibrio versutus strains isolated from soda lakes. The comparative growth kinetics at different Na+ concentration (Chapter 4) showed that Thioalkalivibrio versutus strain ALJ 15 is capable of relatively high rates of sulfur oxidation as compared to the neutrophilic sulfur-oxidizing bacteria. The growth physiology of an extremely salt-tolerant and facultative alkaliphile, Thioalkalivibrio halophilus sp. nov., is presented in Chapter 5. The research concerning the salt-dependent compatible solutes production and membrane lipid composition of haloalkaliphilic sulfur-oxidizing bacteria is the subject of Chapter 6 of this thesis. In the last chapter (Chapter 7) the results are integrated and general conclusions are presented, pointing to the uniqueness and importance of the chemolithoautotrophic haloalkaliphilic SOB for fundamental as well as for applied research. Overall, alkaliphilic SOB isolated from soda lakes proved to be highly specialized for the doubly extreme conditions of high salt concentration and high pH. They can be isolated from soda lake environments only. Some strains tolerate the entire possible range of pH and salt concentrations that might transiently appear in their natural habitat. Based on these properties, the haloalkaliphilic SOB from soda lakes can be usefully exploited in bioreactors with stable soda alkalinity and supplied with inorganic sulfur compounds for sulfur removal from waste streams.Applied Science