SUMMARY Dental caries remains among the most prevalent infectious disease worldwide, costing USA tens of billions of dollars annually in associated care and productivity losses. Dental caries is a result of imbalance of the indigenous microbiota on the tooth surface known as dental plaque, and the acidic metabolites of bacterial metabolism are directly linked to the disease development. It is well understood that conditions like continuous consumption of fermentable sugars, especially sucrose and saliva deficiency favor the emergency of a highly acidogenic and aciduric plaque microbiota, which include Streptococcus mutans and lactobacilli. Lactobacillus (Lb) sp. were the first implicated in dental caries over a century ago, but major gaps remain in knowledge concerning how the different Lb sp. establish and persist in the plaque microbiota and promote the development of carious lesions. In this study, a collection of hundreds of different clinical Lb isolates will be examined using well established in vitro models to elucidate how major groups of Lb sp. colonize and establish on a surface; how S. mutans and environmental conditions may modulate the ability of major Lb sp. to establish and compete in a mixed-species consortium; and how interactions between S. mutans and major Lb sp. influence the community dynamics under conditions typical of the oral cavity. It is highly anticipated that the results from this study will lead to novel insights on each of these aspects and the roles of oral Lb in plaque microbiota and dental caries. Together, the information derived from this study should also serve as a foundation for further investigation on the pathophysiology of oral Lb, the plaque biofilm ecology, and the development of novel strategies against dental caries and other conditions where dysbiotic microbiota is a major underlying factor.