Regulation of urease gene of Actinomyces naeslundii in biofilms in response to environmental factors.

The metabolism of urea by urease enzymes of oral bacteria has a profound influence on oral biofilm pH homeostasis and oral microbial ecology, and Actinomyces naeslundii is an important ureolytic organism in the oral cavity. To gain an insight into the regulation of urease gene expression in cells of A. naeslundii growing in biofilms under different environmental conditions, the behavior of A. naeslundii ATCC12104 was examined in in vitro biofilms. The strain was grown in a chemostat biofilm reactor, and at a quasi-steady state, the urease activity of biofilm cells was measured and transcription of ureC gene was detected with Taqman quantitative PCR. The effect of environmental changes on urease expression was examined by varying the environmental pH, dilution rate, carbohydrate and nitrogen availability of the fluid phase of the culture. The results showed that the conditions of neutral pH, fast dilution rate, increased carbohydrate supply or low nitrogen supply in the medium all resulted in enhancement of urease activity in biofilm cells. But only low nitrogen availability and a fast dilution rate were observed to lead to an increase in ureC mRNA levels. This suggests that nitrogen availability and dilution rate can influence the urease activity of A. naeslundii by modulating ureC gene transcription.