The Rho factor terminates the transcription of specific bacterial genes. Usually, Rho has three conserved domains (N-terminal, RNA-binding, and ATPase). Some species, including mycobacteria, might have Rho with a functional insertion region.

It is important to study how Rho varies among bacteria. However, the last broad analysis of Rho was performed more than ten years ago.

My thesis provides a modern compilation and analysis of the currently known sequence diversity and phylogeny of Rho. Models for each domain were used in a large high-quality genome dataset. The Rho sequences were classified based on the presence and position of the additional regions (Types 1-4).

The typical Escherichia coli like Rho (Type 1) was detected in almost half of the species analysed and atypical forms of Rho were found in most of the other species. The Rho additional regions are predicted to provide extra sites to RNA-binding and to be intrinsically disordered, undergo phase separation, or have prion-like behaviour. Phase separation is an membraneless mechanism of compartmentalization in cells. It allows extra properties, but it is not well characterized in bacteria.

Experimentally, I showed that Mycolicibacterium smegmatis Type 2 Rho forms droplets in vitro by undergoing phase separation. The additional regions of other mycobacterial species also form condensates, and this process is promoted by RNA. Then, I demonstrated that the ability of M. Smegmatis cells to tolerate acid stress is associated with the additional regions of Rho that undergo phase separation in vivo. In contrast, the engineered Rho mutants lacking these additional regions were neither able to tolerate acid stress nor form droplets.

Overall, this study revealed the diversity of atypical Rho factors among bacteria. The Rho additional regions are likely to provide further cellular roles. One example that I showed was the acid tolerance of mycobacteria due to the ability of its atypical Rho to undergo phase separation.

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Zoom link: https://otago.zoom.us/j/97756704741
Meeting ID:  977 5670 4741
Password: bioc