Regulated expression of the Streptococcus mutans dlt genes correlates with intracellular polysaccharide accumulation

被引:47
作者
Spatafora, GA [1 ]
Sheets, M
June, R
Luyimbazi, D
Howard, K
Hulbert, R
Barnard, D
El Janne, M
Hudson, MC
机构
[1] Middlebury Coll, Dept Biol, Middlebury, VT 05753 USA
[2] Univ N Carolina, Dept Biol, Charlotte, NC 28223 USA
关键词
D O I
10.1128/JB.181.8.2363-2372.1999
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
Intracellular polysaccharides (IPS) are glycogen-like storage polymers which contribute significantly to Streptococcus mutans-induced cariogenesis. We previously identified and cloned a locus from the S. mutans chromosome which is required for the accumulation of IFS. Sequencing of this locus revealed at least four contiguous open reading frames, all of which are preceded by a common promoter region and are transcribed in the same direction. Analysis of the amino acid sequence deduced from the first of these open reading frames (ORF1) revealed domains which are highly conserved among D alanine-activating enzymes (DltA) in Lactobacillus rhamnosus (formerly Lactobacillus casei) and Bacillus subtilis. The deduced amino acid sequences derived from ORF2, -3, and -4 also exhibit extensive similarity to DltB, -C, and -D, respectively, in these microorganisms. However, Southern hybridization experiments indicate that this operon maps to a locus on the S. mutans chromosome which is separate from the glgP, glgA, and glgD genes, whose products are known mediators of bacterial IFS accumulation. We therefore assigned a new dlt designation to the locus which we had formerly called gig, We maintain that the dlt genes are involved in S. mutans IFS accumulation, however, since they complement a mutation in trans which otherwise renders S. mutans IFS deficient, In this study, we found that expression of the S. mutans dlt genes is growth phase dependent and is modulated by carbohydrates internalized via the phosphoenolpyruvate phosphotransferase system (PTS). We demonstrated that the S. mutans dlt genes are expressed constitutively when non-PTS sugars are provided as the sole source of carbohydrate. Consistent with a role for the PTS in dlt expression is a similar constitutive expression of the nit genes in an S, mutans PTS mutant grown in a chemically defined medium supplemented with glucose. In summary, these findings support a novel role for the dlt gene products in S. mutans IFS accumulation and suggest that dlt expression in this oral pathogen is subject to complex mechanisms of control imposed by growth phase, dietary carbohydrate, and other factors present in the plaque environment.
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页码:2363 / 2372
页数:10
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