Membrane Vesicles Of Mycobacterium Ulcerans And Their Role In Buruli Ulcer Pathogenesis
Date
2021-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University Of Ghana
Abstract
The release of bacterial extracellular membrane vesicles (EMVs) is essential for pathogen’s
adaptation and virulence. Mycobacterium ulcerans, the causative agent of Buruli ulcer, remains
with queries in its pathogenic mechanism. The current study interrogated biological functions
and protein content of EMVs from viable M. ulcerans’ cells as potential medium of virulence
in BU pathogenesis. Here, we demonstrate release of intact EMVs from the thick cell wall of
log-phase M. ulcerans (Nm 209) as well as M. marinum (Sa 200695) in respective liquid
cultures. Size distributions of isolated EMVs were similar between the two strains and did not
differ from EMVs released by M. smegmatis used as a positive controlled strain. Mycolactone
could not be detected in isolated EMVs from M. ulcerans (Nm 209). However, presence of M.
ulcerans EMVs was associated with higher total intracellular reactive oxygen species which
eventually compromised viability of RAW264.7 cells through oxidative stress. After 48 hours
of co-incubation, native and UV-A irradiated EMVs induced 45% and 40% loss in viability of
RAW264.7 cells, respectively. Moribund phagocytes exhibited apoptotic changes. Proteomic
analysis on the isolated M.ulcerans EMVs revealed an enrichment of 32 unique proteins mostly
localized in the pathogen’s cell wall/membrane. A conserved hypothetical protein
(MUL_2313), had the highest log2 fold change (11.92) followed by Amidase amiC, a cell-wall
remodeling hydrolase (4.19). Others included integral membrane indolylacetylinositol
arabinosyltransferase EmbA/B, and many conserved hypothetical proteins. Direct
contributions of these proteins to EMVs cytotoxicity could not be established. Yet, protein
moon-lighting or possible cross-linking could have potentially contributed to EMV-associated
toxicity on RAW264.7 cells. Our results suggest that M. ulcerans EMVs can elicit toxic
response from host’s macrophage cells through yet to be established mediators. This potentially
reveals new dimension on macrophage-M. ulcerans interactions with possible contribution to
local immunosuppression in BU and paradoxical reactions observed in its treatment.
Description
MPhil. Molecular Cell Biology Of Infectious
Keywords
Mycobacterium Ulcerans, Buruli Ulcer Pathogenesis, Membrane Vesicles