Manoharan, Shathviga (2022) Investigation into the temperature-dependent regulation of virulence factors in Bacillus cereus G9241, the causative agent of an anthrax-like disease. PhD thesis, University of Warwick.

PDF WRAP_Theses_Manoharan_2022.pdf - Submitted Version Embargoed item. Restricted access to Repository staff only until 25 July 2024. Contact author directly, specifying your specific needs. - Requires a PDF viewer. Download (92Mb)

Request Changes to record.

Abstract

Bacillus cereus G9241 was isolated from a Louisiana welder with an anthrax-like illness and is closely related to Bacillus anthracis. Strain G9241 carries the extrachromosomal plasmids pBCX01 and pBC210, each encoding a gene for the mammalian responsive transcriptional regulator AtxA, as well as the linear phagemid pBFH_1. Like most members of the Bacillus cereus group, B. cereus G9241 encodes an intact copy of the gene for PlcR, a pleiotropic transcriptional regulator of secreted toxins and enzymes. Yet all B. anthracis isolates have a point mutation in the plcR gene. It has been proposed that the acquisition of AtxA was incompatible with the activity of PlcR, leading to selection for PlcR inactivation. Interestingly, strain G9241 retains intact copies of both regulators.

Work prior to this study has shown that B. cereus G9241 has a temperature-dependent haemolytic activity, with transcriptomic and proteomic analyses revealing the expression and secretion of haemolysins and toxins regulated by PlcR. Further potential virulence factors were identified; growth phase-dependent elongated cell morphology of B. cereus G9241 was observed during exponential phase growth, similar to the B. anthracis cell shape when evading phagocytes.

This study focussed on investigating the virulence factors that allow strain G9241 to act either as a typical B. cereus strain or an anthrax-causing B. anthracis. Reporter strains for B. cereus G9241 were constructed to identify the expression pattern of plcR-papR and PlcR-regulated toxins. While PlcR demonstrated a highly heterogeneous expression, PlcR-regulated enterotoxins were highly expressed at 25 °C compared to 37 °C. Multiple approaches were used to identify the limiting step within the PlcR-PapR circuit causing the temperature-dependent haemolytic and cytolytic activity in B. cereus G9241. We propose that B. cereus G9241 is able to partially suppress the PlcR regulon in a temperature-dependent manner, potentially to allow the coexistence of plcR and atxA. Inhibitors against cell elongation and cell wall biosynthesis were used to identify the potential mechanism involved in the elongated cell morphology of B. cereus G9241 and its potential function when interacting with immune cells.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QH Natural history Q Science > QH Natural history > QH426 Genetics Q Science > QR Microbiology Q Science > QR Microbiology > QR180 Immunology
Library of Congress Subject Headings (LCSH):	Bacillus cereus, Virulence (Microbiology) -- Genetic aspects, Biosynthesis, Microbiological synthesis, Genetic regulation, Cellular control mechanisms, Cells -- Growth -- Regulation
Official Date:	April 2022
Dates:	Date Event April 2022 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	Warwick Medical School
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Waterfield, Nicholas R. ; Oyston, Petra C. F.
Format of File:	pdf
Extent:	xiv, 273 pages : illustrations
Language:	eng

Request changes or add full text files to a record

Repository staff actions (login required)

View Item