Abstract
Membrane proteins are fascinating since they play an important role in diverse cellular functions and constitute many drug targets. Membrane proteins are challenging to analyze. The spore, the most resistant form of known life, harbors a compressed inner membrane. This membrane acts not only as a barrier for undesired molecules but also as a scaffold for proteins involved in signal transduction and the transport of metabolites during spore germination and subsequent vegetative growth. In this study, we adapted a membrane enrichment method to study the membrane proteome of spores and cells of the food-borne pathogen Bacillus cereus using quantitative proteomics. Using bioinformatics filtering we identify and quantify 498 vegetative cell membrane proteins and 244 spore inner membrane proteins. Comparison of vegetative and spore membrane proteins showed there were 54 spore membrane-specific and 308 cell membrane-specific proteins. Functional characterization of these proteins showed that the cell membrane proteome has a far larger number of transporters, receptors and proteins related to cell division and motility. This was also reflected in the much higher expression level of many of these proteins in the cellular membrane for those proteins that were in common with the spore inner membrane. The spore inner membrane had specific expression of several germinant receptors and spore-specific proteins, but also seemed to show a preference towards the use of simple carbohydrates like glucose and fructose owing to only expressing transporters for these. These results show the differences in membrane proteome composition and show us the specific proteins necessary in the inner membrane of a dormant spore of this toxigenic spore-forming bacterium to survive adverse conditions.
Highlights
The spore-forming organism B. cereus is a human pathogen and is known as a causative agent of food-borne illness
The membrane is a nexus for both perception of the environment as well as import of nutrients and export of signals and components that make up the extracellular parts of an organism
Detailed study of the composition of the membrane protein make-up shows us how various crucial processes at the cell membrane are organized during different stages of the bacterial life cycle of B. cereus
Summary
The spore-forming organism B. cereus is a human pathogen and is known as a causative agent of food-borne illness. The organism synthesizes toxins which lead to diarrheal and emetic syndromes [1] once consumed. Bacterial spore formers such as B. cereus are a main challenge in the manufacturing of stable and safe foods. The spores B. cereus forms are highly resistant to heat, chemicals, UV, desiccation and radiation, making them hard to inactivate during food production. Their thermal resistance is, for a part, due to the presence of dipicolinic acid in the core, where it replaces, to a significant extent, water [2]. Starting from spore core, the layers are the germ cell wall, the cortex, the outer membrane, the coat and the exosporium (Figure 1a)
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