State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China.
J Dent Res. 2013 Sep;92(9):819-24. doi: 10.1177/0022034513498598. Epub 2013 Jul 19.
Although Streptococcus sanguinis has been reported to produce H2O2 to gain a competitive edge over Streptococcus mutans, the molecular mechanisms evolved by S. mutans to counter this "peer stress" are still to be identified. The current study was designed to investigate the ecological role of glutathione synthetase (gshAB) in the interspecies interaction between S. mutans and S. sanguinis. A gshAB in-frame deletion strain of S. mutans was constructed, and its phenotypic traits were characterized. The spatio-temporal interaction of the gshAB mutant with S. sanguinis was further investigated in a dual-species biofilm model by fluorescence in situ hybridization. We found that, although less tolerant for H2O2, the gshAB mutant produced more extracellular polysaccharides by up-regulating gtfs expression, so as to cluster as condensed microcolonies. In addition, the mutant was more susceptible to the conditioned medium of S. sanguinis, and its competitiveness was significantly compromised. Taken together, we believe that gshAB is essential for the competitiveness and prevalence of S. mutans through detoxifying the H2O2 produced by S. sanguinis. Given the ecological importance of bacterial equilibrium within the oral biofilm, gshAB may represent a promising target to modulate the S. mutans/S. sanguinis ratio under cariogenic conditions, thus contributing to the management of dental caries.
尽管已有报道称血链球菌会产生 H2O2 以获得相对于变形链球菌的竞争优势，但变形链球菌进化出的抵御这种“同伴压力”的分子机制仍有待确定。本研究旨在探讨谷胱甘肽合成酶（gshAB）在变形链球菌和血链球菌种间相互作用中的生态作用。构建了变形链球菌 gshAB 框内缺失株，并对其表型特征进行了表征。通过荧光原位杂交进一步研究了 gshAB 突变体与血链球菌在双物种生物膜模型中的时空相互作用。我们发现，尽管对 H2O2 的耐受性较低，但 gshAB 突变体通过上调 gtfs 表达产生了更多的细胞外多糖，从而聚集为浓缩的微菌落。此外，突变体对血链球菌的条件培养基更敏感，其竞争力显著受损。综上所述，我们认为 gshAB 通过解毒血链球菌产生的 H2O2 对变形链球菌的竞争力和流行至关重要。鉴于口腔生物膜内细菌平衡的生态重要性，gshAB 可能成为调节致龋条件下变形链球菌/血链球菌比例的有前途的靶点，从而有助于龋齿的管理。
