Analysis of urease expression in Actinomyces naeslundii WVU45

The hydrolysis of urea by ureases of oral bacteria in dental plaque can cau se a considerable increase in plaque pH, which can inhibit the development of dental caries. There is also indirect evidence that urea metabolism may promote the formation of calculus and that ammonia release from urea could exacerbate periodontal diseases. Actinomyces naeslundii, an early colonizer of the oral cavity and a numerically significant plaque constituent, demon strates comparatively low levels of urease activity on isolation, so this o rganism has not been considered a major contributor to total oral urease ac tivity. In this study it was observed that urease activity and urease-speci fic mRNA levels in A. naeslundii WVU45 can increase up to 50-fold during gr owth under nitrogen-limiting conditions. Using primer extension analysis, a putative, proximal, nitrogen-regulated promoter of the A. naeslundii ureas e gene cluster was identified. The functionality and nitrogen responsivenes s of this promoter were confirmed using reporter gene fusions and 5' deleti on analysis. The data indicated that regulation of urease expression by nit rogen availability in A. naeslundii may require a positive transcriptional activator. Plaque bacteria may experience nitrogen limitation when carbohyd rates are present in excess. Therefore, based on the results of this study and in contrast to previous beliefs, strains of A. naeslundii may have the potential to be significant contributors to total plaque ureolysis, particu larly during periods when there is an increased risk for caries development .