BACILLUS SUBTILIS mitigates BIOFILM FORMATION BY STREPTOCOCCUS MUTANS IN THE PRESENCE OF ALCOHOLIC SUGARS

Bacterial interactions often result in formation of complex structural communities termed biofilms. Natural biofilm usually contains several genetically distinct microorganisms, thus representing a multispecies system. Bacillus subtilis and Streptococcus mutans have been both extensively studied individually as model bacteria for robust biofilm formation. While S. mutans is a leading cause of dental disorders, B. subtilis is considered as non-pathogenic bacterium, which is found mostly in food, such as milk and its products. The aim of this research is to investigate the effect of different dietary sugars on the interaction between B. subtilis and S. mutans during dual-biofilm formation.

B. subtilis and S. mutans cells were grown in co-culture in the presence of different dietary sugars such as: sucrose, lactose, glucose, mannitol, xylitol and sorbitol. The effect of the sugars on bacterial physiology was determined in terms of their growth, metabolic activity and their ability to form biofilm. Generated biofilms were examined for biofilm biomass and biofilm structure.

Our results show that in the presence of non-alcoholic sugars the growth and metabolic activity of each bacterium are notably lower in single culture compared to the co-culture where B. subtilis and S. mutans facilitated each other`s growth and proliferation. Moreover, we found that sucrose and lactose are capable of promoting dual-species biofilm formation. However, S. mutans biofilm was dramatically decreased when both species were grown in co-culture in the presence of alcoholic sugars.

Our findings indicate that B. subtilis and S. mutans contribute to a mutual metabolism of non-alcoholic sugars and forming dual-species biofilm. However, B. subtilis cells can inhibit biofilm formation by S. mutans in the presence of alcoholic sugars.

Acknowledgments: contribution No. 790/17-E, 2017 Series, from the ARO, the Volcani Center. Danielle Duanis-Assaf is a recipient of Scholarship of Excellency for outstanding Ph.D. students from The ARO.