The Effect of Environmental Stress on Outer Membrane Vesicles Biogenesis by Campylobacter jejuni

Majumdar, Rounak (2025) The Effect of Environmental Stress on Outer Membrane Vesicles Biogenesis by Campylobacter jejuni. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Rounak Majumdar (20MS075)) 20MS075_Thesis_file.pdf Restricted to Repository staff only Download (2MB)

Abstract

Campylobacter jejuni (C. jejuni), one of the leading causes of bacterial gastroenteritis around the world, especially in lower- or middle-income developing countries, with substantial mortality and morbidity in humans, particularly in children. Interestingly, C. jejuni lacks the standard secretion systems, unlike other enteric pathogens that deliver virulence factors directly into target cells. On the other side, this bacterium produces outer membrane vesicles (OMVs) containing numerous virulence-associated proteins, including the cytolethal distending toxin (CDT), Cia proteins & serine proteases, which makes OMVs particularly important in causing diseases and bacterial persistence. Under the harsh conditions of the host gastrointestinal tract, OMVs help the bacteria to remove toxic substances and misfolded proteins and maintain homeostasis. Increased OMV production under the influence of physiological concentrations of Sodium taurocholate was observed previously through an unspecified mechanism. Recent models also suggested the role of the maintenance of lipid asymmetry (MLA) pathway as a novel mechanism of OMV biogenesis. In this study, the effect of environmental stress on OMV biogenesis in Campylobacter jejuni was investigated. Quantification of OMVs was carried out using nanoparticle tracking analysis, which was also justified by biochemical assays. Transcriptional expression of cmeABC efflux genes and MLA pathway genes was observed in standard C. jejuni strains TGH 9011 and NCTC 11168 to understand the molecular effects of Bile salt stress on Campylobacter jejuni and its survival strategies. We found that culture with bile salt significantly enhances the OMV biogenesis without impacting OMV size. Further, in vitro transcriptional gene expression analysis revealed that exposure to bile salts, an environmental stressor, leads to the downregulation of the MLA pathway genes, which maintain the outer membrane dynamics in C. jejuni, and also upregulates the cmeABC efflux system gene. Together, the present study demonstrated that C. jejuni OMV biogenesis increased in response to bile salt stress by downregulating the MLA pathway system, which subsequently increases OMV biogenesis, and upregulating the CmeABC efflux system as a compensatory mechanism to mitigate bile-induced stress.

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