Identification of the Immunogenic Spore and Vegetative Proteins of Bacillus anthracis Vaccine Strain A16R

Xiankai Liu,Erling Feng,Dongshu Wang,Xuefang Wang,Hengliang Wang,Chao Tong,Li Zhu,Jingxiao Ren,Daniela Flavia Hozbor

doi:10.1371/journal.pone.0057959

Abstract

Immunoproteomics was used to screen the immunogenic spore and vegetative proteins of Bacillus anthracis vaccine strain A16R. The spore and vegetative proteins were separated by 2D gel electrophoresis and transferred to polyvinylidene difluoride membranes, and then western blotting was performed with rabbit immune serum against B.anthracis live spores. Immunogenic spots were cut and digested by trypsin. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry was performed to identify the proteins. As a result, 11 and 45 immunogenic proteins were identified in the spores and vegetative cells, respectively; 26 of which have not been reported previously. To verify their immunogenicity, 12 of the identified proteins were selected to be expressed, and the immune sera from the mice vaccinated by the 12 expressed proteins, except BA0887, had a specific western blot band with the A16R whole cellular lytic proteins. Some of these immunogenic proteins might be used as novel vaccine candidates themselves or for enhancing the protective efficacy of a protective-antigen-based vaccine.

Highlights

Bacillus anthracis is a Gram-positive bacterium, either aerobic or facultative anaerobic
EA1, which is encoded by the eag gene and has been reported several times before, was found only in the vegetative proteins in the present study
Apart from the two predominant S-layer proteins (EA1 and Sap) on pXO1 previously identified by Okinaka[33], Mock and Fouet were the first to report that the B.anthracis genome harbors additional genes coding for S-layer homology (SLH) proteins that may constitute potential vaccine candidates[34,35]

Summary

Introduction

Bacillus anthracis is a Gram-positive bacterium, either aerobic or facultative anaerobic. It is the causative agent of anthrax, and has been reported as a potential bioterrorism weapon due to its dormant spores that can survive with high stability and low mortality in nutritive conditions and other severe environments[1]. Anthrax infection occurs via introduction of B.anthracis spores into a skin abrasion, inhalation, or ingestion [2]. Inhalation anthrax is the most severe form of the disease and is initiated by uptake of infective spores by alveolar macrophages. The protective antigen (PA) and some other unknown immunogenic proteins of the Bacillus anthracis are able to elicit a humoral immune response in the course of bacterial infections

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