Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA.
Mol Oral Microbiol. 2012 Apr;27(2):70-82. doi: 10.1111/j.2041-1014.2011.00632.x. Epub 2011 Dec 7.
We previously reported that lipopolysaccharide (LPS) -related sugars are associated with the glycosylation of the collagen adhesin EmaA, a virulence determinant of Aggregatibacter actinomycetemcomitans. In this study, the role of LPS in the secretion of other virulence factors was investigated. The secretion of the epithelial adhesin Aae, the immunoglobulin Fc receptor Omp34 and leukotoxin were examined in a mutant strain with inactivated TDP-4-keto-6-deoxy-d-glucose 3,5-epimerase (rmlC), which resulted in altered O-antigen polysaccharides (O-PS) of LPS. The secretion of Aae and Omp34 was not affected. However, the leukotoxin secretion, which is mediated by the TolC-dependent type I secretion system, was altered in the rmlC mutant. The amount of secreted leukotoxin in the bacterial growth medium was reduced nine-fold, with a concurrent four-fold increase of the membrane-bound toxin in the mutant compared with the wild-type strain. The altered leukotoxin secretion pattern was restored to the wild-type by complementation of the rmlC gene in trans. Examination of the ltxA mRNA levels indicated that the leukotoxin secretion was post-transcriptionally regulated in the modified O-PS containing strain. The mutant strain also showed increased resistance to vancomycin, an antibiotic dependent on TolC for internalization, indicating that TolC was affected. Overexpression of TolC in the rmlC mutant resulted in an increased TolC level in the outer membrane but did not restore the leukotoxin secretion profile to the wild-type phenotype. The data suggest that O-PS mediate leukotoxin secretion in A. actinomycetemcomitans.
我们之前报道过，脂多糖（LPS）相关糖与胶原蛋白黏附素 EmaA 的糖基化有关，EmaA 是伴放线放线杆菌的一种毒力决定因子。在这项研究中，我们研究了 LPS 在其他毒力因子分泌中的作用。在一个 TDP-4-酮-6-脱氧-d-葡萄糖 3,5-差向异构酶（rmlC）失活突变株中，检测了上皮黏附素 Aae、免疫球蛋白 Fc 受体 Omp34 和白细胞毒素的分泌情况，该突变株导致 LPS 的 O-抗原多糖（O-PS）发生改变。Aae 和 Omp34 的分泌不受影响。然而，白细胞毒素的分泌受到影响，白细胞毒素的分泌是由依赖 TolC 的 I 型分泌系统介导的，在 rmlC 突变株中发生改变。与野生型菌株相比，突变株中细菌生长培养基中分泌的白细胞毒素减少了 9 倍，而膜结合毒素增加了 4 倍。在 rmlC 基因的反式互补后，改变的白细胞毒素分泌模式恢复到野生型。ltxA mRNA 水平的检测表明，在含有修饰的 O-PS 的菌株中，白细胞毒素的分泌是转录后调控的。突变株还显示出对万古霉素的耐药性增加，万古霉素是一种依赖 TolC 内化的抗生素，这表明 TolC 受到了影响。在 rmlC 突变株中过表达 TolC 导致外膜中 TolC 水平增加，但未将白细胞毒素分泌谱恢复为野生型表型。数据表明，O-PS 介导伴放线放线杆菌白细胞毒素的分泌。
