Chromosome segregation in animal associated bacteria

Bacterial chromosome segregation has been only studied in free-living organisms under controlled culturing conditions. In the course of my PhD, I investigate this fundamental process in Gammaproteobacteria that thrive attached to animal surfaces and cannot be reared in the laboratory. Namely, the longitudinal dividing rod-shaped symbionts Ca. T. oneisti and T. hypermnestrae which are attached by one pole to the surface of their respective nematode hosts. Both rods were shown to widen instead of lengthening and to undergo FtsZ-based longitudinal fission. However, longitudinal fission is asynchronous in Ca. T. hypermnestrae, i.e. FtsZ accumulates first proximally, at the animal-attached pole, and then distally. We hypothesized that the transgenerational attachment of the bacteria, while maintaining a highly ordered arrangement, to a nematode host would affect their chromosome segregation and orientation. Because of the lack of genetic tools, we did use a combination of DNA staining, DNA fluorescence in situ hybridization (FISH) and immunofluorescence labelling to unearth the symbionts’ chromosome biology. Indeed, we found that the monochromosomal symbionts maintain their chromosome orientation toward their respective hosts through a bidimensional segregation mode. Targeting the origin and terminus of replication with specific DNA FISH probes and labelling of an ori-binding chromosome segregation protein (ParB) revealed that chromosomes are segregated along the short axis and that ori and ter occupy specific positions at the beginning and end of the cell cycle. More precisely, in Ca. T. oneisti both localize to the cell center, i.e. transverse configuration of the chromosome, whereas in Ca. T. hypermnestrae the chromosome is arranged longitudinally, with ori detained at the host proximal and ter at the distal pole. Next, we aim to understand whether and how a specific chromosome configuration may serve nematode symbiont physiology.

Student: Philipp Moritz Weber

Faculty: Bulgheresi (PI)

Funding: FWF+ÖAW