ECOLOGICAL COMPETITION AMONG ORAL STREPS

龋齿是人类的一种地方病。 主要病原体 牙齿冠面上的龋齿被认为是变形链球菌 尽管其他细菌也参与了 病变 因此，专门针对S.变形 已被纳入许多治疗和预防性治疗中， 防止龋齿。 其中最近的尝试是， 选择性取代S。非致病性口腔细菌致牙菌斑变链菌 链球菌在牙齿表面占据与S.变异人 理想情况下，人们希望植入一种“更适合”的菌株或突变体， 生态位比原来的占有者S.变异人 因此，它变成了 研究口腔生态竞争重要性和意义 链球菌。 在本申请中，提出研究摄取的作用 葡萄糖、蔗糖和精氨酸的竞争系统， 在营养有限恒化器中混合培养的口腔链球菌。 待研究的生物体是S. mutans Ny344、S. sanguis P4A7和S. milleri B448 营养有限恒化器已被选为模型， 在自然生态系统中看到的营养有限的微生物生长。 每种生物体将在限制葡萄糖、蔗糖或葡萄糖浓度的恒化器中生长。 精氨酸，和Km的吸收这些限制营养素将是 用取自相应恒化器的细胞测定。 然后，混合 从相同数量的S. mutans和S. sanguis或 S. milleri将在限制葡萄糖、蔗糖或 精氨酸，以及两种生物体之间竞争的结果 通过测量培养物中两种生物体的数量来确定， 恒化器达到稳态平衡。 预计该 对限制性养分具有较低Km值的生物将占优势， 混合文化。 该项目提供了获得 生态学观察的生理学解释。

Dental caries is an endemic disease in humans. The primary pathogen of caries on coronal surfaces of teeth is thought to be Streptococcus mutans although other bacteria are implicated in the progression or extension of lesions. Accordingly, measures directed specifically against S. mutans have been included in the many therapies and preventative treatments used against caries. Among the most recent of these have been attempts at the selective replacement of S. mutans in dental plaque by avirulent oral streptococci occupying the same niche on tooth surfaces as S. mutans. Ideally, one would hope to implant a strain or mutant "more fit" for that niche than the originial occupant, namely S. mutans. Thus, it becomes of importance and interest to understand ecological competition among oral streptococci. In this application it is proposed to investigate the roles of uptake systems for glucose, sucrose, and arginine in competition between pairs of oral streptococci grown in mixed culture in a nutrient-limited chemostat. The organisms to be studied are S. mutans Ny344, S. sanguis P4A7, and S. milleri B448. Nutrient-limited chemostats have been chosen as a model for nutrient-limited microbial growth seen in natural ecosystems. Each organism will be grown in a chemostat limited for glucose, sucrose, or arginine, and Km's for uptake of these limiting nutrients will be determined with cells taken from the corresponding chemostats. Then, mixed cultures starting with equal numbers of S. mutans and either S. sanguis or S. milleri will be grown in chemostats limited for glucose, sucrose, or arginine, and the outcome of competition between the two organisms determined by measuring the numbers of the two organisms in the culture as the chemostat comes to a steady state equilibrium. It is expected that the organism having the lower Km for the limiting nutrient will predominate in the mixed culture. This project provides the opportunity to obtain physiological explanations for ecological observations.