Differentiation of Bacillus anthracis, B. cereus, and B. thuringiensis on the basis of the csaB gene reflects host source

Abstract

csaB gene analysis clustered 198 strains of Bacillus anthracis, Bacillus cereus, and Bacillus thuringiensis into two groups related to mammalian and insect hosts, respectively. Mammal-related group I strains also have more S-layer homology (SLH) protein genes than group II strains. This indicates that csaB-based differentiation reflects selective pressure from animal hosts.

Fig 1

Unrooted phylogenetic tree of the csaB genes of B. anthracis, B. cereus, and B. thuringiensis strains. The number at each branch point represents the percentage of bootstrap support calculated from 1,000 replicates. Only bootstrap values above 50 are shown. B.a. Ames* represents all 21 B. anthracis strains. B.c ATCC 14579* represents B. cereus strains ATCC 14579, ATCC 10876, AH676, BAG3X2-2, BAG4X12-1, BDRD-Cer4, F65185, VD156, and VD169. B.t 4AE1* represents B. thuringiensis strains 4AE1, 4AM1, 4AQ1, 4AT1, 4CB1, 4D11, 4G1, 4L1, 4T1, 4W1, 4X1, HD-1, HD73, T03a001, and YBT-1520. B.t ATCC 35646* represents B. thuringiensis strains ATCC 35646, 4AK1, 4AX1, 4BS1, 4BZ1, 4M1, BMB171, Bt4Q7, HD-789, and T69001.

Fig 2

Summary of SLH protein gene distribution. The numbers I and II refer to the two groups shown on the csaB phylogenetic tree in Fig. 1. In the boxes, the bold line represents the median, and the upper and lower boundaries represent the 75th and 25th percentiles, respectively. Group I strains have significantly more SLH protein genes than group II strains (P < 2.2e−16, Mann-Whitney test).