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首页> 外文期刊>Infection and immunity >Characterization of glucosyltransferase-deficient, plasmid-containing mutants of Streptococcus mutans LM-7.
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Characterization of glucosyltransferase-deficient, plasmid-containing mutants of Streptococcus mutans LM-7.

机译：变形链球菌LM-7的葡糖基转移酶缺陷型含质粒突变体的表征。

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摘要

The possibility that glucosyltransferase (GT)-mediated insoluble-glucan synthesis from sucrose is controlled by the 3-megadalton plasmid pAM7 in Streptococcus mutans LM-7 has been examined. A low-sucrose agar medium was developed to readily detect and quantitate presumptive GT-negative mutants. Such mutants were isolated from Todd-Hewitt broth cultures grown either with or without sodium dodecyl sulfate (10 microgram/ml) or acriflavine (0.5 microgram/ml) at frequencies ranging from about 0.01 to 1%. Independently isolated mutants had the following characteristics: (i) cells were virtually devoid of cell-associated GT and did not aggregate upon addition of sucrose; (ii) cell-free culture fluids synthesized 10X less insoluble glucan than those of the parent; and (iii) cultures grown with sucrose did not form adherent deposits on the wall of the culture tube, as is typical of S. mutans. Both parent and mutants formed relatively little soluble glucan in 1-h assays. Three independently isolated mutants and the parent were found to contain similar amounts of plasmid DNA. Analysis by sucrose density gradient centrifugation and agarose gel electrophoresis did not reveal a size difference between the plasmids from parent and mutants. These results show that (i) S. mutans LM-7 generates GT-deficient mutants at relatively high frequency that still contain a 3-megadalton plasmid; (ii) both cell-associated and extracellular GT levels are depressed in the mutants, which suggests that these activities are directly or indirectly controlled by the same gene or by genes that segregate as a unit.
机译：已经研究了由变形糖链球菌LM-7中的3-megadalton质粒pAM7控制由蔗糖进行的葡糖基转移酶（GT）介导的不溶性葡聚糖合成的可能性。开发了低蔗糖琼脂培养基，可轻松检测和定量推测的GT阴性突变体。从含有或不含十二烷基硫酸钠（10微克/毫升）或isolated啶黄素（0.5微克/毫升）的Todd-Hewitt肉汤培养物中分离出此类突变体，其频率为约0.01-1％。独立分离的突变体具有以下特征：（i）细胞实际上没有细胞相关的GT，并且在添加蔗糖后不会聚集; （ii）无细胞培养液合成的不溶葡聚糖比母体少10倍; （iii）用蔗糖培养的培养物没有像变形链球菌那样在培养管壁上形成附着的沉积物。亲本和突变体在1-h分析中均形成相对较少的可溶性葡聚糖。发现三个独立分离的突变体和亲本含有相似量的质粒DNA。通过蔗糖密度梯度离心和琼脂糖凝胶电泳的分析未显示出来自亲本和突变体的质粒之间的大小差异。这些结果表明（i）变形链球菌LM-7以相对较高的频率产生GT缺陷的突变体，其仍然含有3-megadalton质粒; （ii）突变体中细胞相关和细胞外GT水平均降低，这表明这些活性直接或间接地由同一基因或以一个单位分离的基因控制。

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