Raffinose Induces Biofilm Formation by Streptococcus mutans in Low Concentrations of Sucrose by Increasing Production of Extracellular DNA and Fructan

Abstract

Streptococcus mutans is the primary etiological agent of dental caries and causes tooth decay by forming a firmly attached biofilm on tooth surfaces. Biofilm formation is induced by the presence of sucrose, which is a substrate for the synthesis of extracellular polysaccharides but not in the presence of oligosaccharides. Nonetheless, in this study, we found that raffinose, which is an oligosaccharide with an intestinal regulatory function and antiallergic effect, induced biofilm formation by S. mutans in a mixed culture with sucrose, which was at concentrations less than those required to induce biofilm formation directly. We analyzed the possible mechanism behind the small requirement for sucrose for biofilm formation in the presence of raffinose. Our results suggested that sucrose contributed to an increase in bacterial cell surface hydrophobicity and biofilm formation. Next, we examined how the effects of raffinose interacted with the effects of sucrose for biofilm formation. We showed that the presence of raffinose induced fructan synthesis by fructosyltransferase and aggregated extracellular DNA (eDNA, which is probably genomic DNA released from dead cells) into the biofilm. eDNA seemed to be important for biofilm formation, because the degradation of DNA by DNase I resulted in a significant reduction in biofilm formation. When assessing the role of fructan in biofilm formation, we found that fructan enhanced eDNA-dependent cell aggregation. Therefore, our results show that raffinose and sucrose have cooperative effects and that this induction of biofilm formation depends on supportive elements that mainly consist of eDNA and fructan.IMPORTANCE The sucrose-dependent mechanism of biofilm formation in Streptococcus mutans has been studied extensively. Nonetheless, the effects of carbohydrates other than sucrose are inadequately understood. Our findings concerning raffinose advance the understanding of the mechanism underlying the joint effects of sucrose and other carbohydrates on biofilm formation. Since raffinose has been reported to have positive effects on enterobacterial flora, research on the effects of raffinose on the oral flora are required prior to its use as a beneficial sugar for human health. Here, we showed that raffinose induced biofilm formation by S. mutans in low concentrations of sucrose. The induction of biofilm formation generally generates negative effects on the oral flora. Therefore, we believe that this finding will aid in the development of more effective oral care techniques to maintain oral flora health.

Capacity To Utilize Raffinose Dictates Pneumococcal Disease Phenotype

“…Interestingly, exogenous raffinose has recently been shown to promote biofilm formation by Streptococcus mutans by promoting aggregation of extracellular DNA into the biofilm matrix. Biofilm formation was unaffected by deletion of the α-galactosidase gene agaL , indicating that the effect was unrelated to metabolism of any internalized raffinose (22). Thus, it is conceivable that the reduced capacity of S.…”

Biochemical characterization of extracellular polymeric substances from endodontic biofilms

“…So far, what has been described in the literature in relation to ROF components raffinose-induced biofilm formation by S . mutans in a mixed culture with sucrose [ 27 ]. Further, it has been reported that contribute to the extracellular polysaccharides production in some oral bacteria [ 28 ].…”

The fructan syndrome: Evolutionary aspects and common themes among plants and microbes

“…Inulin is known to be an important part of the biofilm produced by oral Streptococcus mutans , and inulin accumulating in dental plaques is hydrolysed when environmental carbon sources are scarce, which in turn may cause dental carries in the long run (Krzyściak, Jurczak, Kościelniak, Bystrowska, & Skalniak, ). Nagasawa, Sato, and Senpuku () studied the effects of sucrose and raffinose, a trisaccharide composed of ᴅ‐galactose, ᴅ‐glucose, and ᴅ‐fructose, on biofilm formation of S. mutans, and found that at sucrose concentrations insufficient to induce biofilm formation, raffinose contributed to biofilm structure by increasing aggregation of eDNA while also being a substrate for raffinose‐based inulin production. Because the ᴅ‐glucose moiety in raffinose is located between the other two monosaccharides, glucosyltransferase enzymes cannot use raffinose as donor substrate to synthesize glucans.…”