Investigation of the CtrA cell cycle master regulator in Bartonella quintana

Abstract

<p><strong>This research project aimed to address the gaps in knowledge surrounding Bartonella quintana, with a specific focus on understanding its cell cycle dynamics and the mechanisms underlying its virulence. B. quintana is an intriguing pathogen due to its ability to persist for long periods within the human vascular and intraerythrocytic environment. Specifically, for B. quintana to reside inside erythrocytes without causing lysis, tight regulation of the cell cycle is required to limit its replication within this niche.</strong></p><p>CtrA is known as a master regulatory protein controlling the cell cycle in multiple alpha-proteobacteria, including C. crescentus. This study aimed to shed light on how this protein influences the cell cycle or morphology of B. quintana. The primary objective was to investigate the role of CtrA as a transcription factor within B. quintana and to evaluate the impact of CtrA overexpression on the bacterium.</p><p>I first used a bioinformatics approach to identify B. quintana promoters that contained putative CtrA binding motifs. I then used a beta-galactosidase assay to investigate the impact of heterologous CtrA protein expression on the activity of two identified promoters, ftsH and ftsK. The ftsH homologue gene in C. crescentus encodes a zinc metalloprotease that is required for the stress response and that plays a role in cell division. The ftsK homologue encodes an essential protein that coordinates cell division and chromosomal segregation. The results suggested a potential repressive role of CtrA on the ftsH gene within B. quintana. Expression from the ftsK promoter, however, was not detected, either with or without CtrA.</p><p>Because CtrA is an essential protein in most alpha-proteobacteria, I attempted to construct a conditional mutant. Although this strain could not be achieved in this project, the strain carrying the complementation plasmid was used to study the effects of CtrA overexpression in B. quintana. Distinct outcomes were noted in terms of viability and chromosome content between the wildtype B. quintana and those carrying the inducible ctrA plasmid. Differences in morphology were not noted, but this could be due to the lack of time available to optimise microscopy protocols.</p><p>The alteration in viability and chromosomal contents observed, when ctrA expression was induced on a plasmid, suggests a potential role for CtrA in the cell cycle of B. quintana. Further investigation is warranted to explore the functions of CtrA in B. quintana, not only in the context of the cell cycle but also in other aspects of B. quintana morphology and pathogenesis.</p>