Graduate Students Mini Symposium XII - 2024

13:15 h Philipp Klos - AG Sogaard-Andersen

Analysis of the activation of the ParA/MinD ATPase PomZ by the phase-separating protein PomY

In most bacteria, cell division crucially depends on the tubulin-homolog FtsZ, which polymerizes to form the cytokinetic Z-ring at the division site. The diverse systems that position the Z-ring, all modulate FtsZ polymerization. In Myxococcus xanthus, PomX, PomY, and PomZ form precisely one MDa-sized non-stoichiometric, nucleoid-associated co-condensate per cell that positions the Z-ring. In this system, PomX and PomY drive the translocation of the PomXYZ co-condensate across the nucleoid to midcell by stimulating the ATPase activity of the DNA-bound ParA/MinD ATPase PomZ. At midcell, the PomY condensate enriches FtsZ, thereby nucleating its polymerization. Here, we demonstrate that PomY activates PomZ ATPase activity by a non-canonical mechanism and that activation does not depend on phase separation.

13:45 h Ina Biazruchka - AG Sourjik

Reversible control of bacteria persistence

Bacteria cells can tolerate environmental stress such as antibiotic treatment, nutrient limitation, oxidative stress, heat shock and many other stressful factors by forming persister cells. In this project, we aim to develop an approach that enables the controlled and reversible induction of the phenotypic switch from normal growing state to the persister-like state in Escherichia coli cells. We established a model system with a persistence-inducing toxin HokB. When the local concentration of toxins reaches a certain threshold, HokB forms a pore in the membrane, resulting in the activation of the persistence state. We managed to induce toxins oligomerization in a controlled way, by expressing a modified version of HokB toxin from plasmid. We demonstrated that the population of cells induced by our system possessed physiological traits associated with persisters. The established technique is found to be very promising for studying metabolism and physiology of the bacteria cells under growth arrest and upon awakening from this state.

14:15 h Holly Addison - AG Rebelein

Two distinct ferredoxins are essential for nitrogen fixation by the iron nitrogenase in Rhodobacter capsulatus

Nitrogenases are the only enzymes able to ‘fix’ atmospheric N₂ into bioavailable NH₃ and hence are essential for sustaining biological life. Nitrogenase catalysis is dependent on an ample supply of both ATP and electrons, the latter provided by low-potential redox proteins, often ferredoxins (Fds). Regarding this electron transport to nitrogenase proteins, many open questions remain. Our goal was to identify which Fds are important for nitrogen fixation by the Fe-nitrogenase and try to elucidate their functions. Through the characterisation of Rhodobacter capsulatus strains with genetic deletions of the Fd genes (fdx), we identified two essential Fds for nitrogen fixation by the Fe-nitrogenase. Specifically, the deletion of two fdx genes, fdxC and fdxN, slowed diazotrophic growth rates, lowered Fe-nitrogenase activities and caused upregulations of proteins involved in electron transport to the Fe-nitrogenase. Our current research has focused on studying FdN and FdC in vitro. Specifically, FdN and FdC have been characterised spectroscopically, structurally and biochemically. Overall, our findings have provided two key protein targets for the further study and bioengineering of nitrogen fixation systems, specifically those focussed on engineering the electron flux to nitrogenases.