Abstract
Mung bean nuclease treatment of 16S-23S ribosomal DNA intergenic transcribed spacers (ITS) amplified from several strains of the six species of the
Bacillus cereus
group showed that
B. anthracis
Davis TE702 and
B. mycoides
G2 have other intermediate fragments in addition to the 220- and 550-bp homoduplex fragments typical of the
B. cereus
group. Long and intermediate homoduplex ITS fragments from strains Davis TE702 and G2 and from another 19 strains of the six species were sequenced. Two main types of ITS were found, either with two tRNA genes (tRNA
Ile
and tRNA
Ala
) or without any at all. Strain Davis TE702 harbors an additional ITS with a single tRNA gene, a hybrid between the tRNA
Ile
and tRNA
Ala
genes, suggesting that a recombination event rather than a deletion generated the single tDNA-containing ITS. Strain G2 showed an additional ITS of intermediate length with no tDNA and no similarity to other known sequences. Neighbor-joining analysis of tDNA-containing long ITS indicated that
B. cereus
and
B. thuringiensis
represent a single clade. Three signature sequences discriminated
B. anthracis
from
B. cereus
and
B. thuringiensis
, indicating that the anthrax agent started evolving separately from the related clades of the
B. cereus
group.
B. mycoides
and
B. weienstephanensis
were very closely related, while
B. pseudomycoides
appeared the most distant species.