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Chapter 12 : Bacillus anthracis
Category: Applied and Industrial Microbiology; Food Microbiology
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Bacillus cereus is the putative ancestor of all Bacillus anthracis strains, which obtained two virulence plasmids (pXO1 and pXO2) and at least one chromosomal mutation that inactivated the plcR gene. Identification of the molecular signals that trigger germination and the spore surface receptors involved is critical to understanding the pathogenesis of B. anthracis. Sporulation and pathogenesis are opposite processes, while germination and virulence gene expression are synergistic, since transition from dormant spores to vegetative cells is essential for the virulence of B. anthracis. One of the enzymes within the basal layer of B. anthracisspores is an alanine racemase capable of converting the spore germinant L-alanine to the germination inhibitor D-alanine. Comparative genomic studies have contributed significantly to our understanding of the virulence properties, host specificity, ecology, and adaptations of B. anthracis and other species comprising the B. cereus group. While all Banthracis strains examined so far contain four prophages of the lambda family inserted at defined loci, most of the other sequenced B. cereus group genomes do not contain homologous prophages inserted at these sites. With the advent of next-generation sequencing technologies, which promise to deliver even more sequence data over shorter periods of time, and with metagenomics and community genomics approaches on the rise, the future of pathogen genomics is bright and growing fast.
Phylogenetic tree representing the evolution of B. anthracis. B. cereus is the putative ancestor of all B. anthracis strains, which obtained two virulence plasmids (pXO1 and pXO2) and at least one chromosomal mutation that inactivated the plcR gene.
Dot plot homology analysis of the Ames strain lbclA gene. A sliding window (nine nucleotides) is used with two different match criteria (A, 100%; B, 70%) to compare the bclA gene sequence with itself to identify repeated regions. This figure was kindly provided by Mr. James Schupp (Northern Arizona University).
Mauve alignments of B. anthracis Ames ancestor and Ames chromosomes with near neighbors B. cereus E33L, B. thuringiensis 97-27, and B. thuringiensis Al Hakam.
Genome map of the B. thuringiensis Al Hakam circular phage pALH1. Top blastp hits are indicated below each ORE. This phage has a mosaic structure, but the coding sequences share the highest similarity with other B. cereus phage, prophage, and plasmid sequences. Arrows are shaded based on the origin of the top hit: polka dots indicate that the top hit of the Al Hakam phage coding sequence was to B. cereus G9241; diagonal lines, B. cereus 03BB108; cross-hatching, B. cereus W; burlap, top hit was to both B. cereus 03BB108 and B. cereus W; plaid, B. cereus 059799; capsules, Bacillus phage IEBH; vertical lines, single hits to additional B. cereus genomes; solid white, B. anthracis; solid black, little or no similarity; black with white spots, top hit to phage sequence from non-B. cereus species.
Mauve (left column) and MUMmer (right column) alignments of the Al Hakam phage sequence with other B. cereus group phage and plasmid sequences. From top to bottom, panels A to C show alignments of the Al Hakam phage sequence with the B. cereus G9241 pBClin29 prophage region (A), the B. cereus W plasmid PW_87 (B), and the B. cereus 03BB108_42 plasmid (C).
Exosporium gene neighborhoods in B. anthracis Ames and Ames ancestor compared to other B. cereus group genomes. Genes with analogous functional categories are colored the same in each genome. This comparative view of the gene neighborhoods was generated using the Integrated Microbial Genomes system (http://img.jgi.doe.gov/).
General features of Bacillus anthracis and near neighbor genomes
Sporulation and germination genes