A tale of adaptation Diversity and stress responses in the haloalkaliphilic sulfur-oxidizing bacteria of the genus Thioalkalivibrio

Soda lakes are extreme environments with a pH of around 10 and salt concentrations up to saturation. Moreover, other factors might impose various types of stress on the microbial communities in soda lakes, including fluctuating salinities and temperatures, high UV radiation or the occurrence of heavy metals such as arsenic. Despite these harsh conditions, soda lakes support diverse microbial communities. One of the most abundant bacterial genera found in soda lakes is Thioalkalivibrio. Strains of this genus are obligate haloalkaliphilic chemolithoautotrophic sulfur-oxidizing bacteria that are grouped within the Gammaproteobacteria. Currently, there are more than 100 strains, but not all were affiliated to one of the ten described species by phylogenetic and phylogenomic analyses. Therefore, these taxonomic analyses were performed in this thesis and revealed in total 25 ‘genomic’ species within the genus Thioalkalivibrio and that the genus is not monophyletic. Furthermore, these extremophiles are perfectly adapted to the haloalkaline conditions, but only little is known on how they respond to the various other stressors present in soda lakes. To improve our understanding on their molecular and physiological response mechanisms to other stress factors, this thesis focuses on the stress that is induced by arsenite, low temperature and antibiotics using, amongst others, comparative sequence analysis and transcriptomics. Our results show that members of the genus Thioalkalivibrio are well equipped to thrive in the extreme environments of soda lakes, which allowed them to persist under multiple stressful conditions and to become a dominant community member in these lakes.