REGULATION OF STREPTOCOCCUS GORDONII GLUCOSYLTRANSFERASE

早期定植的牙菌斑细菌，如戈登链球菌，形成基质，后来定植的微生物物种，包括潜在的病原体，在成熟的牙菌斑发育过程中附着在基质上。gordonii单葡萄糖基转移酶（GTF）酶水解蔗糖形成葡聚糖聚合物，可以促进细菌在表面积聚。GTF的活性水平会影响godonii细胞在体外定植表面的能力，从而可能影响其在体内建立生态位的能力。已知环境和生长条件会影响S. gordonii GTF活性。GTF结构基因gtfG的表达受上游决定因子rgg的正调控。在高水平和低水平的GTF活性之间经历可逆的相位变化。虽然GTF相变化的分子基础尚不清楚，但rgg或gtfG的核苷酸变化或重排是不必要的；因此，位于远端的DNA与gtfG表达的控制有关。这些研究的工作假设是，戈登氏球菌GTF活性的调控涉及复杂的分子相互作用，可能对戈登氏球菌在口腔中的生存具有生态学意义。本研究的主要目标是：1)通过结构和遗传学研究，确定rgg调控gtfG的分子机制；2)利用报告基因融合鉴定影响rgg和gtfG表达的远端戈登链球菌基因；3)确定影响gtfG及其调控基因表达的环境条件；4)利用随机随机引物PCR技术，鉴定受遗传或环境因素影响GTF活性而表达水平发生改变的其他gordonii基因。希望这些研究将提供一个分子相互作用的理解和条件，有利于或不利于共生生物葡萄球菌生产葡聚糖。从长远来看，这些信息可能提供对控制和可能选择健康口腔菌群的因素的见解，并可能在开发基于生物学的治疗方案中实施。

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.