Y. Yamashita et al., MOLECULAR AND GENETIC-ANALYSIS OF MULTIPLE CHANGES IN THE LEVELS OF PRODUCTION OF VIRULENCE FACTORS IN A SUBCULTURED VARIANT OF STREPTOCOCCUS-MUTANS, FEMS microbiology letters, 144(1), 1996, pp. 81-87
We previously isolated a variant strain, Xc100L, which shows decreased
production of a surface protein antigen with a molecular mass of 190
kDa (PAc), after repeated subculturing of Streptococcus mutans strain
Xe [Koga, T. et al. (1989) J. Gen. Microbiol. 135, 3199-3202]. In the
present study, the levels of expression of the gtfB, gtfC, gtfD and ft
f genes coding for polysaccharide-synthesizing enzymes in strain Xc100
L were compared with those in strain Xc. Western blot analysis reveale
d multiple differences in the levels of production of these enzymes be
tween these two strains. The amounts of the gtfB and gtfC gene product
s responsible for water-insoluble glucan synthesis in strain Xc100L we
re lower than those in strain Xc, whereas the amounts of the gtfD and
ftf gene products responsible for water-soluble glucan synthesis and f
ructan synthesis, respectively, in strain Xc100L were higher than thos
e in strain Xc. Northern blot analysis revealed that the amounts of th
e four enzymes and PAc produced by strain Xc100L reflected the relativ
e amounts of mRNAs from the genes. The chloramphenicol acetyltransfera
se gene was fused with each of these five genes, and the transcription
al activity of each gene in strain Xc100L was quantitatively compared
with that in strain Xc. The chloramphenicol acetyltransferase assay al
so indicated that the phenotypic differences between strain Xc and str
ain Xc100L were due to differences in the transcriptional activities o
f the virulence genes. No differences in the nucleotide sequences of t
he promoter regions of the gtfB, gtfC, gtfD, ftf and pac genes were fo
und between strain Xc and strain Xc100L. It is possible that a factor(
s) affecting the levels of transcription of the multiple virulence gen
es exists in S. mutans.