University Archives

Background: V. parvula (Vp) and S. mutans (Sm) cooperate within biofilms to cause dental caries. V. parvula metabolizes lactic acid produced by S. mutans to propionic and acetic acids. This leads to enhanced overall biofilm health while maintaining a demineralizing pH of ~pH=5. V. parvula relies upon the lactate utilization operon, lutABC, to deacidify S. mutans biofilms.

Objectives: To metabolize lactate to pyruvate (on the way to propionate and acetate) under anaerobic conditions, V. parvula uses a series of iron-sulfur cluster proteins, LutABC, that can transfer electrons and allow for the generation of ATP. Our goal is to define the terminal electron acceptor in the V. parvula LutABC system, since oxygen is not available.

Methods: Biofilms of Sm (ATCC 25175) alone or in combination with Vp (ATCC 10790) were grown in artificial saliva + 0.5% sucrose +/- nitrate. 4.3mM nitrate or 5mM fumarate (another terminal electron acceptor of anaerobes) was added back to artificial saliva lacking nitrate to determine if nitrate was required for biofilm deacidification. The health of Sm + Vp biofilms was assessed by LIVE/DEAD staining.

Results: Biofilms of Sm + Vp grown in the absence of nitrate were no longer able to deacidify Sm biofilms, and resembled biofilms of Sm alone and a Vp lutABC mutant. Addition of nitrate or fumarate back to artificial saliva restored deacidification, indicating nitrate or fumarate can serve as terminal electron acceptors in the LutABC system. LIVE/DEAD imaging also indicated nitrate plays a role in LutABC-dependent biofilm health in mixed Sm + Vp biofilms.

Conclusions: Under anaerobic conditions, V. parvula uses nitrate or fumarate to deacidify S. mutans biofilms. This process relies on the LutABC system. Future studies will explore polymicrobial biofilms including other species that can utilize and deplete nitrate, perhaps impacting the role of Vp in Sm biofilm deacidification.