This PhD thesis presents results of a research focussed on the evolution of phototrophy in the bacterial order Rhodobacterales with a special regard to its haloalkaliphilic representatives. The photoheterotrophic bacterium Rhodobaca barguzinensis alga05 was used as an organism of choice. Its phylogeny, genome organization, and metabolic potential was characterized. The main result of the thesis is that phototrophy is a genuine trait among the haloalkaliphilic representatives of the Rhodobacter-Rhodobaca group inside the Rhodobacterales clade.

Marine microbiome research is a rapidly expanding field of study, as scientists investigate the functions of microbial associations in eukaryotic organisms. Foraminifera are among the most abundant shelled organisms in the oceans, yet little is known of their associated microbiomes. This study investigated microbes associated with four species of Foraminifera that host three kinds of algal endosymbionts. The Order Miliolida, Family Soritidae, was represented by three species: Archaias angulatus and Cyclorbiculina compressa, which both host chlorophyte symbionts, and Sorites orbiculus, which hosts dinoflagellate symbionts. The fourth species, Amphistegina gibbosa, belongs to the Order Rotaliida and hosts diatom endosymbionts. Bacterial DNA extraction was attempted from 5−8 specimens per species followed by amplification and amplicon sequencing of the V4 variable region of the 16S rRNA gene. Three Ar. angulatus specimens shared 177 Operational Taxonomic Units (OTUs), and six C. compressa specimens shared 58 OTUs, of which 31 OTUs were found in all specimens of both species. Four S. orbiculus specimens shared 717 OTUs dominated by Proteobacteria, notably Amoebophilaceae. The three soritid species shared 26 OTUs, predominantly representing the bacterial families Rhodobacteraceae and Flavobacteriaceae. Since S. orbiculus shared 84% of the OTUs shared by Ar. angulatus and C. compressa, which host similar endosymbionts, phylogenetic relatedness of host taxa clearly had more influence on core microbiomes than the algal-symbiont taxon. The microbiomes of three normal-appearing and five partly-bleached specimens of Am. gibbosa varied widely, sharing only six OTUs, four of which represented Proteobacteria. All four species shared only four OTUs, three of which may have been contaminants. As the first known microbiome study to include western Atlantic/Caribbean benthic foraminifers that host algal endosymbionts, the results for Am. gibbosa revealed quite similar results to a recent study of the microbiome of Am. lobifera, a closely related Indo-Pacific taxon.

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