Zeng Lin, Farivar Tanaz, Burne Robert A
Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USAStanford University
Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USAStanford University.
Appl Environ Microbiol. 2016 May 31;82(12):3671-82. doi: 10.1128/AEM.00637-16. Print 2016 Jun 15.
Biochemical and genetic aspects of the metabolism of the amino sugars N-acetylglucosamine (GlcNAc) and glucosamine (GlcN) by commensal oral streptococci and the effects of these sugars on interspecies competition with the dental caries pathogen Streptococcus mutans were explored. Multiple S. mutans wild-type isolates displayed long lag phases when transferred from glucose-containing medium to medium with GlcNAc as the primary carbohydrate source, but commensal streptococci did not. Competition in liquid coculture or dual-species biofilms between S. mutans and Streptococcus gordonii showed that S. gordonii was particularly dominant when the primary carbohydrate was GlcN or GlcNAc. Transcriptional and enzymatic assays showed that the catabolic pathway for GlcNAc was less highly induced in S. mutans than in S. gordonii Exposure to H2O2, which is produced by S. gordonii and antagonizes the growth of S. mutans, led to reduced mRNA levels of nagA and nagB in S. mutans When the gene for the transcriptional regulatory NagR was deleted in S. gordonii, the strain produced constitutively high levels of nagA (GlcNAc-6-P deacetylase), nagB (GlcN-6-P deaminase), and glmS (GlcN-6-P synthase) mRNA. Similar to NagR of S. mutans (NagRSm), the S. gordonii NagR protein (NagRSg) could bind to consensus binding sites (dre) in the nagA, nagB, and glmS promoter regions of S. gordonii Notably, NagRSg binding was inhibited by GlcN-6-P, but G-6-P had no effect, unlike for NagRSm This study expands the understanding of amino sugar metabolism and NagR-dependent gene regulation in streptococci and highlights the potential for therapeutic applications of amino sugars to prevent dental caries.
Amino sugars are abundant in the biosphere, so the relative efficiency of particular bacteria in a given microbiota to metabolize these sources of carbon and nitrogen might have a profound impact on the ecology of the community. Our investigation reveals that several oral commensal bacteria have a much greater capacity to utilize amino sugars than the dental pathogen Streptococcus mutans and that the ability of the model commensal Streptococcus gordonii to compete against S. mutans is substantively enhanced by the presence of amino sugars commonly found in the oral cavity. The mechanisms underlying the greater capacity and competitive enhancements of the commensal are shown to depend on how the genes for the catabolic enzymes are regulated, the role of the allosteric modulators affecting such regulation, and the ability of amino sugars to enhance certain activities of the commensal that are antagonistic to S. mutans.
研究了共生口腔链球菌对氨基糖N-乙酰葡糖胺（GlcNAc）和葡糖胺（GlcN）的代谢的生化和遗传方面，以及这些糖对与龋齿病原体变形链球菌种间竞争的影响。多个变形链球菌野生型菌株从含葡萄糖培养基转移到以GlcNAc作为主要碳水化合物来源的培养基时表现出较长的延迟期，但共生链球菌没有。变形链球菌与戈登链球菌在液体共培养或双物种生物膜中的竞争表明，当主要碳水化合物为GlcN或GlcNAc时，戈登链球菌特别占优势。转录和酶活性分析表明，GlcNAc的分解代谢途径在变形链球菌中的诱导程度低于戈登链球菌。暴露于由戈登链球菌产生并拮抗变形链球菌生长的H2O₂会导致变形链球菌中nagA和nagB的mRNA水平降低。当戈登链球菌中负责转录调控的NagR基因被缺失时，该菌株组成性地产生高水平的nagA（GlcNAc-6-P脱乙酰酶）、nagB（GlcN-6-P脱氨酶）和glmS（GlcN-6-P合酶）的mRNA。与变形链球菌的NagR（NagRSm）类似，戈登链球菌的NagR蛋白（NagRSg）可以结合到戈登链球菌nagA、nagB和glmS启动子区域的共有结合位点（dre）。值得注意的是，NagRSg的结合受到GlcN-6-P的抑制，但G-6-P没有影响，这与NagRSm不同。本研究扩展了对链球菌中氨基糖代谢和NagR依赖性基因调控的理解，并突出了氨基糖在预防龋齿方面的治疗应用潜力。
氨基糖在生物圈中很丰富，因此特定微生物群中特定细菌代谢这些碳源和氮源的相对效率可能对群落生态产生深远影响。我们的研究表明，几种口腔共生细菌利用氨基糖的能力比口腔病原体变形链球菌强得多，并且模型共生菌戈登链球菌与变形链球菌竞争的能力因口腔中常见的氨基糖的存在而显著增强。共生菌能力更强和竞争增强的潜在机制表明取决于分解代谢酶基因的调控方式、变构调节剂对这种调控的作用，以及氨基糖增强共生菌某些拮抗变形链球菌活性的能力。
