School of Dental Medicine, University of Connecticut Health Center, Farmington, CT, USA.
School of Dental Medicine, State University of New York at Buffalo, Buffalo, NY, USA.
J Oral Microbiol. 2014 Jan 29;6. doi: 10.3402/jom.v6.23419. eCollection 2014.
Candida albicans co-aggregates with Streptococcus gordonii to form biofilms and their interactions in mucosal biofilms may lead to pathogenic synergy. Although the functions of glucosyltransferases (Gtf) of Mutans streptococci have been well characterized, the biological roles of these enzymes in commensal oral streptococci, such as S. gordonii, in oral biofilm communities are less clear.
The objective of this work was to explore the role of GtfG, the single Gtf enzyme of S. gordonii, in biofilm interactions with C. albicans.
Biofilms were grown under salivary flow in flow cells in vitro, or under static conditions in 96 well plates. A panel of isogenic S. gordonii CH1 gtfG mutants and complemented strains were co-inoculated with C. albicans strain SC5314 to form mixed biofilms. Biofilm accretion and binding interactions between the two organisms were tested. Biofilms were quantified using confocal microscopy or the crystal violet assay.
The presence of GtfG enhanced dual biofilm accretion, and sucrose supplementation further augmented dual biofilm formation, pointing to a role of newly synthesized glucans. GtfG also promoted binding to C. albicans preformed biofilms. Soluble α-1,6-glucans played a role in these interactions since: 1) a strain producing only soluble glucans (CH107) formed robust dual biofilms under conditions of salivary flow; and 2) the dual biofilm was susceptible to enzymatic breakdown by dextranase which specifically degrades soluble α-1,6-glucans.
Our work identified a novel molecular mechanism for C. albicans and S. gordonii biofilm interactions, mediated by GtfG. This protein promotes early biofilm binding of S. gordonii to C. albicans which leads to increased accretion of streptococcal cells in mixed biofilms. We also showed that soluble glucans, with α-1,6-linkages, promoted inter-generic adhesive interactions.
白色念珠菌与戈登链球菌共聚集形成生物膜，它们在黏膜生物膜中的相互作用可能导致致病协同作用。虽然变异链球菌的葡糖基转移酶（Gtf）的功能已经得到很好的描述，但这些酶在口腔共生链球菌，如戈登链球菌中的生物学作用在口腔生物膜群落中还不太清楚。
本研究旨在探讨戈登链球菌唯一的 Gtf 酶 GtfG 在与白色念珠菌生物膜相互作用中的作用。
在体外流动细胞或 96 孔板中静态条件下，通过唾液流培养生物膜。一组同基因戈登链球菌 CH1 gtfG 突变体和互补菌株与白色念珠菌 SC5314 共同接种以形成混合生物膜。测试了两种生物之间的生物膜附着和结合相互作用。使用共聚焦显微镜或结晶紫测定法对生物膜进行定量。
GtfG 的存在增强了双生物膜的附着，蔗糖的补充进一步增强了双生物膜的形成，这表明新合成的葡聚糖起作用。GtfG 还促进了与预先形成的白色念珠菌生物膜的结合。可溶性α-1,6-葡聚糖在这些相互作用中起作用，因为：1）仅产生可溶性葡聚糖的菌株（CH107）在唾液流条件下形成了强大的双生物膜；2）双生物膜易受葡聚糖酶的酶解，葡聚糖酶特异性降解可溶性α-1,6-葡聚糖。
我们的工作确定了白色念珠菌和戈登链球菌生物膜相互作用的一种新的分子机制，该机制由 GtfG 介导。这种蛋白质促进了戈登链球菌对白色念珠菌的早期生物膜结合，导致混合生物膜中链球菌细胞的附着增加。我们还表明，具有α-1,6-键的可溶性葡聚糖促进了种间粘性相互作用。
