Decipher the role of late lytic genes activator, a key determinant of active lysogeny in Listeria monocytogenes

Listeria monocytogenes (Lm) is an intracellular bacterial pathogen. Lm strain 10403S harbors an active prophage in its genome integrated within the comK gene.

It was previously discovered by the Herskovits lab (host lab) that during Lm infection of macrophages, the prophage undergoes excision from comK, yielding an intact and functional comK gene that assists the escape of the bacteria from the macrophages’ phagosomes to the cytosol.

Notably, this phage excision does not lead to virion production and bacterial lysis in the mammalian environment, suggesting a cooperative phage behaviour.

It was further shown that the phage early genes are transcribed in the intracellular niche, whereas the late lytic genes are not, thereby preventing the progression of the lytic pathway.

This type of adaptive phage behaviour was termed “active-lysogeny”, representing cases where prophages cooperate with their hosts.

To better understand active-lysogeny in Lm, in this BacPro proposal I aim to decipher the mechanism by which the late lytic genes are repressed in the intracellular niche.

It was previously demonstrated that the late genes are positively regulated by LlgA, an ArpU-family transcriptional regulator that is encoded by the phage. Preliminary data in the lab indicate that LlgA is thermo-regulated at the protein level.

LlgA regulation at the temperature of the mammalian niche was shown to relay on the bacteria, and to involve a mechanism similar to regulated proteolysis. Based on these findings, in my proposal I aim to identify the bacterial proteases that are involved in its cleavage. Further I aim to determine LlgA active form, as well as its cleavage site/s.

These studies will provide a molecular insight into the mechanism by which Lm controls the phage in the mammalian environment, and further increase our understanding of how lysogenic phages interact with bacterial pathogens, an information that might lead to a better design of phages for the use of phage therapy.