Molecular Ecology of the NOR5/OM60 Groupof Gammaproteobacteria

Abstract

In this thesis, a newly discovered gammaproteobacterial group - the NOR5/OM60 clade, which includes the novel aerobic anoxygenic phototrophs (AAnPs), was studied in the aspects of phylogeny, biogeography and physiology using both molecular and culturing methods.By means of 16S rRNA phylogenetic analysis, NOR5/OM60 group was defined as a monophyletic clade inside the class Gammaproteobacteria. More than 500 16S rRNA sequences of this clade were retrieved from public databases. Further studies classified the sequences into 13 subclades. My studies on the biogeography of NOR5/OM60 clade showed a cosmopolitan distribution. They were found in all oceans and at the coasts of all the continents. NOR5/OM60 seems to be most abundant in marine coastal water and sediment. However, they have also been encountered in surface water of open ocean, deep-sea sediment, freshwater, saline lakes and soil.The abundance of members of the NOR5/OM60 clade in various marine sites was determined by fluorescence in situ hybridization (FISH) with a newly designed and optimized probe set. In the ocean, the common relative abundance ranges from <1% in the open ocean to about 10% in the North Sea coastal water. The existence in coastal sediment and freshwater was also proved by FISH.More than 30 strains of the NOR5/OM60 clades had been isolated as pure cultures in several studies. Of these, the genomes of five strains (KT71, RAp1red, Ivo14, HTCC2080 and HTCC2148) were fully sequenced. In this thesis, these five genomes were compared to each other and to a closely related strain, HTCC2143 from the BD1-7 group. The photosynthesis (PS) superoperon, the key genes of 3-hydroxypropionate cycle for carbon fixation, and the sox operon for sulfur compound oxidation were found in four strains: KT71, RAp1red, Ivo14 and HTCC2080. Genomic comparison indicated that, like KT71, many NOR5/OM60 members may also be AAnPs and potentially be able to use light as energy source.