REGULATION OF STREPTOCOCCUS GORDONII GLUCOSYLTRANSFERASE

早期定植的牙菌斑细菌，如戈登链球菌，形成了后来定植的微生物物种，包括潜在的病原体，在成熟的菌斑发展过程中附着的底物。戈登链球菌单葡糖基转移酶(GTF)酶能分解蔗糖，形成葡聚糖聚合物，促进细菌在表面堆积。GTF活性水平影响戈登链霉菌细胞在体外表面定植的能力，因此可能影响它们在体内建立生态位的能力。已知的环境和生长条件会影响戈登氏链球菌的GTF活性。GTF结构基因gtfG的表达受上游决定簇RGG的正调控。戈登氏链霉菌在高水平和低水平的GTF活性之间经历可逆的相变。虽然GTF时相变化的分子基础尚不清楚，但RGG或gtfG中的核苷酸改变或重排是不必要的；因此，远端DNA参与了gtfG表达的调控。这项研究的工作假设是，戈登螺旋体中GTF活性的调节涉及复杂的分子相互作用，这可能对戈登螺旋体在口腔中的生存具有生态学意义。拟议研究的目标是确定参与控制戈登链球菌GTF活性的环境信号和遗传元件，其目的有四个：1)通过结构和遗传学研究表征RGG调节gtfG表达的分子机制；2)利用报告基因融合来确定影响rgg和gtfG表达的远端基因；3)确定影响gtfG及其调控基因表达的环境条件(S)；4)使用随机引物聚合酶链式反应，鉴定其他戈登链球菌根据影响gtf活性的遗传或环境因素，表达水平发生变化的基因。希望这些研究能提供对共生生物S.gordonii产生葡聚糖有利或不利的分子相互作用和条件的了解。从长远来看，这些信息可能提供对控制并可能选择健康口腔菌群的因素的洞察，并有可能在基于生物的治疗方案的开发中实施。

Early colonizing dental plaque bacteria such as Streptococcus gordonii, form the substratum to which later-colonizing microbial species, including potential pathogens, attach in the process of mature plaque development. The S. gordonii single glucosyltransferase (GTF) enzyme hydrolyzes sucrose to form glucan polymers that can facilitate bacterial accumulation on surfaces. The level of GTF activity affects the ability of S. gordonii cells to colonize surfaces in vitro and therefore, may affect their ability to establish in ecological niches in vivo. Environmental and growth conditions are known to affect S. gordonii GTF activity. Expression of the GTF structural gene, gtfG, is positively regulated by the upstream determinant, rgg. S. gordonii undergo a reversible phase variation between high and low levels of GTF activity. Although the molecular basis for GTF phase variation is not known, nucleotide changes or rearrangements in rgg or gtfG are not necessary; thus distally- located DNA is implicated in the control of gtfG expression. The working hypothesis of the proposed studies is that regulation of GTF activity in S. gordonii involves complex molecular interactions that may have ecological implications for survival of S. gordonii in the oral cavity. The goal of the proposed studies, to identify environmental signals and genetic elements involved in control of S. gordonii GTF activity, will be pursued in four specific aims: 1) to characterize the molecular mechanism of rgg regulation of gtfG through structural and genetic studies; 2) to use reporter genes fusions to identify distally-located S. gordonii genes that affect rgg and gtfG expression; 3) to identify environmental conditions that affect expression of gtfG and its regulatory gene(s); 4) to use random arbitrarily primed PCR to identify additional S. gordonii genes that show altered levels of expression in response to genetic or environmental factors that affect GTF activity. It is hoped that these studies will provide an understanding of the molecular interactions and conditions that favor or disfavor glucan production by the commensal organism S. gordonii. In the long term, such information may provide insights into factors which control, and possibly select for, a healthy oral flora and potentially be implemented in the development of biologically based therapeutic regimens.